Im new here so go easy, I will probably have a ton of questions. As the subject eludes, I am thinking strongly of a 4107. I like that they are only 35 foot, the large bays, and that there are no wheel wells protruding into the floor. Otherwise I would probably go with an 06.
I am leaning toward converting one myself, otherwise probably redoing an existing one. Money is tight so I have to limit my budget by doing as much as I can on my own.
One of my main concerns are how the 4107's really handle. Ive read some about them blowing around in stiff crosswinds, can anyone offer some better comparisons? I presently run an old oshkosh bounder with a cummins 5.9 pusher, I cant imagine a 4107 blowing around as much as that, but I wounldnt know.
Another big question is needing service out on the road. Motorhomes are actually pretty risky machines to leave home with, RV dealers wont work on the chassis, and truck shops wont generally work on motorhomes. How about a bus, will truck stops let one of those in?
Then there are the real questions. Heating and cooling systems, power generation, etc.. I would like it to be as efficient as possible, as well as able to remain unplugged as long as possible. So RV fridge is a given. I have read some threads here discussing using the engine alternator to run roof airs, and ditching the OTR system. I would prefer a ducted a/c system in the floor, and probably in floor heat. Heat could be either diesel or propane. Generator will be diesel. Any thoughts on keeping the large OTR condensor and incorporating it into a different system???
All thoughts and experiences are welcomed.
Welcome to the madness! I have an AMGeneral 40 x 102 wide transit that I love since it is 6 inches wider and has 6'10" of headroom. With cooling, heating, stay with main stream proven technology. For instance many like the Diesel heat of Aqua Hot (around $8,000), but also look at the maintenance on that system. I have a propane furnace (just replaced it after 15 years), and 3 burner propane stove with oven. Everything else is electric. Two 10 gal electric water heaters-one feeding into the next with the final one powered through the inverter for hot water during the day when driving. Two Shurflo Whisper water pumps plumbed in parallel for smoother flow. 3 roof top A/C's (no dash air), 10kw Diesel Generator, 130gal water, 85 gal gray, 45 gal black, 2-8D AGM house batteries, 2-31 starting batteries with solenoid to jump the two sets if need be, 6.3cu/ft Norcold refer, 2.1 cu/ft Norcold chest freezer, 20 gal chassis mount propane, 2 Fantastic Fans, etc. Just an idea what I've done-except for replacing the propane furnace (I left it on for 2 weeks) nothing else has needed replacement in 15 years. Good Luck, TomC
Thanks for the response, sounds like youve done a lot of neat work. I want to try as hard as possible to stay away from RV type heating and cooling. I want to keep the roof clear, I just dont like the clutter of a/c units and vents on the roof of a bus.
For heat I am thinking of using a short or modified gas (LP) hot water heater and in floor heating, with a loop for hot tap water, and an engine preheat loop. For cooling I am thinking I'll use the factory a/c condensor, and plumb in a small residential A/C compressor and run duct work to floor vents. With some extra work I could possibly reverse it into a heat pump for back up heat. Thats the direction my thinking is going anyway. If I can get it insulated well, for such small space I shouldnt need a very large compressor, maybe a 1 1/2 ton compressor??? I really would like the engine alternator to be able to provide enough electrical power for cooling without taxing it too hard, and I believe this should accomplish that with power to spare.
Art -
I'm in the minority here, but am also one of the few with real-world industry experience, too. Needless to say, I hated the 4107/8s that were in the charter bus fleet when I worked that industry back in the late '70s - mid '80's. They weren't second-hand junkers, either - they'd been bought new from GMC by a company that has a meticulous preventative maintenance program.
Loved the 4106s and the 4905s, still do.
You do mention their pluses - the large bays, the lack of wheel well "humps" and the 35' overall length. You missed the pantograph bay doors - very handy in tight places.
You don't mention their major minuses:
~~ The stadium seating up front that takes away nearly 5' of interior space, which is critical in a 35' coach to begin with. Sure, you can level the floor, but you end up banging your head on the vista windows in the process. Can be remedied with a front cap covering a roof raise, but on a tight budget? Not quite as much of an issue with a 40-foot 4905, but still lost space.
~~ The kneecap-destroying dashboard switch layout, especially if you're short and have to have the seat closer to the dash for pedal access. Can be remedied with a Sawzall, or purchasing a 4108 instead.
~~ A lot more steel in the construction, leading to lots more corrosion repair. Most noticeable around the two "d" windows, among other spots.
~~ The cantankerous crosswind handling. IMHO, the 4107 and it's younger sister the 4108, both suffer the same fate. They are far more stable than your typical stick 'n staple Winnibuggy, but for a bus chassis, they're skittish. It's my theory that the large "sail area" presented by the taller roofline, combined with the 35' length, contribute to this behavior. The five-foot longer 4905 does not suffer the same consequence - the longer wheelbase creates a much more stable base, not to mention a sweet ride.
This is NOT to say that some owners don't share these same opinions, because that's all they are from an industry vet dealing with revenue-service vehicles. In RV use, most folk park 'em when it gets really windy, so their experience is different.
If you're hooked on a 35' Buffalo, I'd suggest a 4108, due to the far better OEM dashboard if nothing else. Harder to find, tho, due to lower production volume.
As for converting one yourself, be aware that in today's economic climate, there is NO WAY you can do a conversion for less $$$ than you can buy one already finished and ready to roll, maybe needing just a little TLC. Think about what I just said very carefully, there are a LOT of abandoned project buses out there.
Truck stops are more than willing to let their mechanic learn all about bus systems on your dime. OK for an oil change (bring your own oil & filters) and brake adjustment (especially if they have a pit), but for more, you need a friendly local charter bus company garage that takes on outside work. Or one of their mechanics who moonlights.
The topic of HVAC for bus conversions can get quite entertaining, and the debate rages on. Do a search of the archives for lots of thoughts on the subject, much of what you're thinking about has already been cussed/discussed over the years. Use the search button in the upper LEFT for better results. Oh, and search the archives over on BNO, too (www.busnut.com (http://www.busnut.com)) for more entertainment. There are a couple of busnuts on this board (Nick & Christy) who own HVAC businesses and are a wealth of knowledge, they can provide valuable assistance.
Hope that's enough to get you started thinking. Remember that buying a bus is easy, selling a mistake is HARD! Do your homework, and find a good BUS mechanic you can trust and work with.
FWIW & HTH. . .
;)
Good information, thank you. Its valuable to have someone that has experience.
If you could elaborate on the crosswind skittishness? As I said, I am presently pushing a 32' Bounder with a cummins. It gets buffeted in stronng crosswinds, but its nothing I cant handle. If you could better detail what your saying I would love to hear.
I'm a mechanic, so the bus doesnt scare me mechanically, but I cant take a full workshop out on the road. If I need repairs or service to the coach away from home, im very interested as to how truck garages accept them. They downright refuse to work of "RV's". For example I wanted some brake work done when I lived in the Minneapolis area. RV dealers wouldnt work on it, and neither would truck shops. On the road ive had some minor issues, and truck stops turned me away. The few ive spoken to would not have even serviced a tire! At least a bus is heavy duty enough that if ready to roll I may never need their services. Just nice to know.
As to the stadium seating, I really need to get back out and look at them some more, its been a while, but as I recall I will still have more floor space than I do now with this Bounder. Its 32 feet, but between the side door screwing up the floor plan and the dash and seats sitting back 5 feet taking up the whole front nose, I figure I would still get a good gain of space.
Another question is these busses climbing abilty and ground clearance.
I have a very long (1/4 mile) and steep driveway with a short turn in off the highway. The bounder wont drag it butt , but it has a longer rear overhang than a bus. What about a 4107? They dont have as much overhang, but they sit much lower. I never blew up the bags on a bus as far as they could go, but does anyone know how much ground clearance could be had by fully inflating the air bags? I dont mind scraping some if im not hurting anything, but id prefer not to scrape anything at all.
And how steep a grade can they go up in first gear? The initial part of the drive is nearly 30% and I dont have any run to reach any speed to make power. I need to be able to climb the drive at just a bit above idle speed.
Ive been assuming both these questions are non issues, but we all know what assuptions cause us.
Art, these buses will climb about 20% in first gear if they are a standard shift; try to avoid starting uphill on any steep grade.
With a three speed automatic, they will climb a steeper grade, and these will make starting on a steep grade easy. They will make a lot of heat before the converter locks up.
TomC can give you ratios and startability calculations as he is very familiar with them.
At 2100 RPM, our standard shift gives us about 20 in first, 34 in second, 57 in third and 83 in fourth. The three speed auto will cost you about 10% of the top end.
By using these forums and getting a book like Bus Garages(?), you will find there is quite a bit of help out there.
Good luck.
Tom Caffrey
Art,
Steep driveway! Its a fairly tall first gear and the detroit is not a low speed torque monster. ;D
There is almost overhang at the rear. From the rear axle its bulkhead then engine.
Air bags pressed up full will raise the bus about 4-5". I added air leveling, auto level stopped via electric valves, and I could move a corner some 8-10" with the combination of no air and opposite corner at max pressure.
First bus we had was a 4108. Loved how it drove. Somewhat sensitive to crosswinds. Come out from an underpass and watched the semi in front shift half a lane while I moved about two feet. That was a nasty wind at exactly 90 degrees to travel. One of the cures for the lower front seats is to build the floor level. The steps down must allow the tallest family member to walk down by the vista window without ducking their head. Works well. That's the penalty you pay for the tall bays.
Bill
Based on a V730 with a bus weighing in at 32,000lb and with a 4.1 rear axle ratio, and 12R-22.5's, with a 65 injector 8V-71 getting 800lb/ft torque, you can expect a startability of 20.5% gradability. That's OK, but should be higher. I know I would have gotton stuck a few times with that setup. On my bus at 32,000lb, 1125lb/ft torque, 4.56 rears, and 11R-24.5's, that works out to be 31.5% startability-which made last years drive over Ebitts pass on highway 4 (some 27% grades) possible. Now my truck will be a real stump puller. Based on what I think will be a 38,000lb truck, 1325lb/ft torque, HT740, 3.55 gears, 11R-24.5, my startability should be around 40%! I doubt I'll ever get stuck on a hill. Good Luck, TomC
Wow, lots of response, thanks guys.
I wont be looking at a bus with an auto. I will simply accept the bus was meant to be a manual and master it. I wont need to start out from a stop on my 20% grade drive, I have a lil bit of run at it. I was just checking to be sure I could maintain momentum once I start up. The bounder always stalls to a stop for a second or two before it gains full boost and starts moving again. I sure wouldnt want a standard trans bus to lose power there which is why I was asking.
Secondly, I intend to keep wieght to a minimum and run it as light as possible. No granite, no heavy oak, and not bringing everything including the kitchen sink. And I wont be dragging the toad up the drive, ill drop it down below and drive up solo.
So by what your all saying I shouldnt have any problem once the clutch is engaged, just punch it and go? Then all I have to be concerned with is clearance. When you say an additional 4-5 inches with full up bags, what are you talking for overall clearance? 12-14"? More? Thanks
Art- before buying the bus, you must bring it home to see if will pull the driveway. Try both a manual and an automatic bus. I am relatively sure, you'll choose the automatic-I know I would, and I did (this after driving 1.3 million miles with a 13 spd).
If you're on a hill with a manual, and you do slip the clutch enough to not stall the engine, that is not a guarantee that there will be enough power to keep it from stalling out. Personally-I just don't think 4 or a 5 spd is enough gears for what we run into. If you had at least a 6, more like a 7 spd, then I'd say OK. Trust me when I say, you'll get your bus into situations that were not intended for a bus to be in. And a couple of burned clutches, maybe a tow or three to get you out of the bind you're in, you could have paid for that automatic transmission. Once again-be sure to drive both the manual and automatic transmission bus up your driveway!! Good Luck, TomC
Art
I have to agree with Tom C on auto vs manual. I've had both. The auto is the way to go for a conversion. I had to replace a clutch on the 4108. It is a day's job for two guys who are familiar with the GM system.
Tom's comment that we go places that buses aren't made to go is entirely correct. An auto makes it easier to recover from the error.
Regarding clearance - i would say that with one end on low air and the other on max maybe 10" change in height. Never did measure actual clearance.
Bill
I know an automatic makes it all easier, and I do really appreciate all the good advice. But my feeling is that fuel is going to become very expensive in the future and were going to be squeezing for every mpg we can to be able to afford to go anywhere. It seems that if a guy can keep one of these under 60 mph, 11, maybe 12 mpg and possibly a squeak more is possible. But 8 seems to be pushing it with an auto bus, and 6 to 7 seems more the norm. I get 6 and 7 now, 8 if I keep it under 65, and that adds up. Anything to gain some range will be of benefit.
Yes,I understand there are things more important than fuel economy, but ive put 45K on this bounder now, and fuel has been the biggest operating expense. At roughly 2.80 per gallon average over the last 4 years at 7 mpg, thats cost roughly $18K in fuel. A 4 mpg increase over that same distance would have either saved me $7k, or allowed me to travel another 26000 miles. Thats a free trip around the world! Another way to look at it is that fuel could double to $6 gallon, but not really cost me anymore to operate than what im pushing now. If I do get a bus, its going to be a stick and I will have to make or break it.
'04 will get you better milage.....but it really won't get you up that driveway. if you use another driver driving the toad the toad might give you enough oooomph to get you up driveway.
Art -
Re-reading your previous posts brings out these questions and comments:
How much of a straight run do you have at the hill before starting up? Enough to get the coach to the governor in 1st gear? (Approx 400 feet, give or take a little.)
If you can't get the coach to the governor in 1st before you hit the bottom of your driveway, you're gonna get lots of practice backing downhill. Don't ask me how I know this - BTDT!
I've seen many a Muni bus in San Francisco have to stop and let passengers off the coach in order for it to get started on the hills around Candlestick Park after a ball game. And these were 8V71 / V-730 transit buses with 5:56 rear axles - a LOT lower-geared than the 4:125:1 in the 4107s.
There is an alternative, and that's one of the (RARE) S-50/VR-731 combination, or the S-50/Voith combination powerpacks used in some mid-'90's transits. Nimco might have a few. . . Caveat: These would be SMOG engines, so very de-tuned from potential, and virtually impossible to get Detroit to bump them up. In transit service they're set for 275 hp, same as the stock 8V71 in a 4107. 330 or 350 hp for highway bus/bobtail truck operations, but NOT with the V-drive.
Not sure of the ground clearance amidships or at the back bumper, but the DA BOOK calls for 14" between the ground and the top of the bottom step at the front door.
OTOH, a later-model coach with a 400+ hp four-stroke coupled to a five-speed automatic probably wouldn't have any problems climbing your driveway. Eh, TomC?
Added after your last post:
Hate to burst your bubble, but you'd be VERY, VERY, lucky to get 11 - 12 mpg with an 8V71-powered manual-gearbox 4107/8, most likely downhill with a strong tailwind. The norm is 7-8, and I can show you my now-ancient logbooks to prove it. I used to put 80,000 a year on these beasts back in my charter days, had to fuel them during or after each run, and the company insisted that the mileage and amount of fuel be listed on our logbook sheets as well as the fuel card in the coach.
A 4104 will, if driven frugally, return 10 -11 mpg, but wouldn't have the hp or torque to make it up your driveway.
Range, OTOH, is a different story. A 4107 will easily cover 1,000 miles on a tank of fuel @ 65 mph, but it will take 125 - 135 gallons upon fillup (they have a 165 gallon tank).
Fuel will be your biggest operating expense regardless of the vehicle - even your own car.
FWIW & HTH. . .
;)
I have less than half a bus length before the grade. I do not have 15 bus lengths. I may have to completely re-think all this. There would be no purpose to back up and re try. If it cant make it up the first time, more tries wont change anything. Either it can make a 20% grade or it cant. Sounds like it cant.
Everything I have read and discussed over the years has been that 4107's could range between 9 and 11 mpg. There are some posts/threads on this site that claim that, but maybe they are fudging numbers. 7-8 is pretty awful, and something else I will have to re-think carefully. I would be curious how you drove these, if you drove to reach best economy, or to make time. How fast did you generally run on the interstate? I remember when they were out on the road alot in my younger days, most were hard to keep up with as they were rolling 75-80 mph and some more than that.
Art -
The company I worked for had the engines governed at 1900 rpm max, compared to the usual 2150. This translated to a top speed of 70 mph.
However, every coach also had a "tattletale" (tachograph - google it if you don't know what they are), the drivers had to turn in the discs after every trip. Those caught running over 65 mph for any length of time were disciplined and/or fired. Period.
This was also back in the days of the idiotic 55 mph National Speed Limit, so the vast majority of runs were made at 60, give or take a couple mph.
I'm also in Central CA. Every trip we take to anywhere, be it SF or LA, Tahoe or Vegas, requires us to climb 6% grades to get out of this valley. 70 miles of 4, 5 & 6% grades going to Reno, NV, on I-80 out of Sacramento, for example. Or the 6% on the Grapevine (I-5) to LA. That kills fuel mileage when you have to plug along in 2nd gear for miles on end. From Barstow to Vegas on I-15, besides the notorious Baker Grade, there are miles of subtle grades where the coach won't pull it in fourth, but will sit easily on the governor in 3rd, again, killing the fuel mileage.
(Let me rephrase that last sentence - the bus would pull those subtle grades in 4th, but you'd spend a bunch of time sitting along the highway with an overheated engine to do so.)
That's my real-world revenue-service experience. Those who operated these in the prairie states, where it's miles and miles of flat land as far as the eye can see, probably have different fuel mileage figures.
I do know a fellow who likes to say he gets 13 mpg with his 4905: 6 in town and 7 on the highway. 6 + 7 = 13 mpg! ;D
Be aware that a 4107/8, stripped to a shell, probably weighs more than your Bounder, fully loaded. We're talking 20,000 lbs, empty/stripped.
Your driveway is really the biggest challenge you have. If your Bounder has problems with it, the bus is going to be worse: heavier, lower ground clearance, manual gearbox, less low-end torque.
Continue doing your homework. If you can find a 4107/8 in your neighborhood, TomC's suggestion of bringing it by your house to try getting it up the driveway before buying one is a good idea.
Good Luck!
FWIW & HTH. . .
;)
I spoke too soon maybe. I took several measurments to be able to give you guys a better picture.
The steepest part of the drive is 23%, which occurs about 150 feet up from the bottom. Beginning down at the road I have about one bus length (40 feet) to accelerate from almost a dead stop before the grade starts, which increases to 18% within another 40 feet. (IOW, From a dead stop I will be on an 18% grade within two bus legths). It stays at 18% for about 50 feet and then increases to 23%. It is only 23% for about 50 feet farther, at which point the grade immediately levels off to 11% and remains at that grade for another 1400 feet up to my house. Backing down would not be fun. If I can keep accelerating up the 18% part of the grade, I think I should be able to carry enough momentum to clear the 23% part and then im home free. If you guys dont think it can make the 18% part, then its never going to make it over the hump.
I know the 4107 is about 20k empty. What I dont know is what it will weigh rigged out. But I do plan to build it very light. I used to build pickup campers. Light ones had 3/4" x 1 1/2" lumber walls and cabinets with 1/8" ply. Heavy ones used 2x4's with 1/4 ply. The light 11 footers four people could carry, the heavy 9 footers 10 people couldnt pick up. Ive read of some bus conversions with the inside sheeted out with 1/4 ply. Oak cabinets. Granite counters and floors. Some of these no doubt exceed their original GVWR. I have planned to build this to keep weight down as low as possible.
7-8 mpg in mountains is pretty reasonable, I could live with that. The bounder does about 6-9 on level road, 5 and worse in heavy grades. Most of my travels will be midwestern flatland on US highways with littlle interstate. From what I have researched the 8-71 likes to run at around 1200-1400 to achieve best fuel economy and I would try to size the tires to run at that engine speed at about 55 mph. Does this sound reasonable?? I know a lot of the bus drivers drive foot to the floor, but I would probably nurse it up to speed as much as possible as long as I didnt have traffic behind me. Ive nursed over 50 mpg out of my 190 diesel Mercedes driving that way.
My dream for over 10 years is to someday drive to Alaska. I dont know if it will ever happen, but if it does it would be awesome to do it in a bus. Using the toad to help push it up the driveway would make quite a difference and is a wonderful idea I hadnt thought of. Its a 4x4 Jeep Cherokee, so we could put it into low range and give it the boot. I think that problem may be solved??
Art -
GVWR is an issue primarily with stick 'n staple Winnibuggies. Many exceed their ratings after the water tank's been filled, fuel's been topped off, and mom & dad have loaded up their "stuff" for the trip. Often dangerously so.
Not the case with most bus conversions (except for the rolling whorehouse models with granite everywhere and fourteen slide-outs). The vast majority of GMC 35-foot conversions weigh in between 25K - 27K ready to roll. The coach has a 32K GVWR, so you've normally got 5 - 7K worth of margin.
If you're going to strip it to a shell, THE most important thing you can do is insulate it well - spray foam is the best, hands down. Light weight and extremely efficient. Why do you think every refer trailer pounding the Interstates are insulated with spray foam? Slightly more expensive up front, but payback is much greater. Oh, and it makes a HUGE difference in the noise level inside this big steel/aluminum drum.
Since you were involved with building camper shells, you know that 1/8" ply is NOT going to hold up as well as 1/4", especially for walls. 1/8" is commonly used here for ceilings, due to the greater flexibility w/o any real loading. These beasts do flex going down the highway, the better you build it, the better it will withstand the road.
Based on my experience, I'd say an automatic-equipped GMC coach would struggle getting up your driveway with the info you've provided, but would make it - barely. If the engine had a turbo, boosting hp to 350/370 hp over the stock 275, it would pull the hill better.
No go with a manual box though - they're geared too high. And sorry, no other manual gearbox is available for a V-drive coach. Turbo wouldn't help here, you don't have room to get the rpm up high enough for the boost to assist. At least without smoking the clutch - a real no-no in a bus! :'(
Pushing with the toad might work, but it might also destroy the tow bar in the process. And depending on how the hitch is mounted to the coach, it might do some strange things to the engine cradle, too - ouch! (The bumper is NOT mounted to the coach frame - the coach doesn't have a frame! The engine cradle, which the bumper is attached to, literally hangs from the roof of the bus.)
1200 - 1400 are the torque peaks for the 8V71, depending on whether it's standard or advanced timing. This rpm range is not the "sweet spot" of the engine - it's the range that will get you into overheating trouble if you run for extended periods with a load on the engine.
Quickly.
VERY quickly with ambient air temps above 85o or so.
A little GM engineering history here for you: The powertrain of the GM highway coach, from the pre-WWII Yellow 719s and 743s on, was designed around tires that turn 495 revs per mile, with a rear axle ratio of 4.125:1 for the 35-foot models, and 4.375:1 for the later 40-footers. Remember that magic number - 495. It's important when you're sizing tires for a GM.
Six-cylinder models got a bevel gear ratio of 1:1, whereas the eight cylinder buses got an overdrive 0.808 with the manual. With the 1:1 4th gear in the Spicer, the overall final drive ratio for the sixes is 4.125:1, the eights come in at either 3.333:1 (35') or 3.535:1 (40').
For the 4106/7/8 with the 8V71 / 4-spd manual, this results in 60 mph at 1650 rpm - just under the sweet spot of 1700. The forty footers run 100 rpm higher at the same road speed, due to the lower rear axle ratio.
Remember, this is with tires that turn 495 revs per mile. Buy taller tires (that turn less than 495), and you'll turn fewer engine rpm at the same road speed. Buy shorter tires (turning more than 495 rpm), and you get the opposite effect. The closer they are to 495, the closer you'll be to OEM performance.
For example, Bridgestone makes a drive tire (M726EL) that turns 470 rpm. That tire will give you 65 mph at 1650 rpm - 5 mph faster than stock. But you're lugging the engine if you try to run 55 mph with it - you're down at 1400. Good way to burn up a motor.
HOWEVER -
That same tire, if the coach has been converted to a V-730 automatic, gives you 60 mph @ 1650 rpm - exactly the same as OEM with the manual box. A lot of GM owners run the larger tire to compensate somewhat for the lower bevel gearing in the automatic.
Must add a caveat here: The taller tires, while they'll help with the fuel mileage out on the highway, will also make it harder to get up your driveway - especially if you still have a stick shift!
One other point: The two-stroke Detroit climbs grades best on a partial throttle between 1700 - 1900 rpm. You should be able to accelerate somewhat if you add more throttle while in this range. Black smoke means you've got your foot in it too far, back out. If you do and your coach maintains it's speed, you were wasting fuel and creating unnecessary heat. If you do and the coach starts slowing, it's time to grab the next lower gear. Very simple. Follow that guideline and it would be extremely rare to overheat a GMC (providing the cooling system has been maintained properly).
I've covered a lot with this post, might take a few minutes to digest. TomC possibly can assist with the different torque and grade capability of the turbocharged 350 hp engine, compared to the naturally-aspirated 275 hp stock engine. Just to give you some more data to ponder, of course.
FWIW & HTH. . .
;)
After reading all of this 2 thoughts come to mind. It sounds like instead of trying to get up your driveway with a bus, you would be a lot better off to find a place close to home where you could store it/work on it.....or move! ;D Second, besides the other advice against pushing it with your jeep, if your driveway is paved you do not want to have your jeep in 4 wheel drive.....unless you want to start replacing transfer cases, etc. >:( Good luck with this, hope you can figure out something that will work out for you. Ps. i have a 5A with an 8V71 and an auto tranny and get between 7-8 mpg....mostly right around 7.25 mpg. I am in the western US.... Wa. in the summers and Az in the winters, so i have a few passes to go over no matter how i go.
how often are you going to go up the drive? If it's rarely I am leaning more towards a pull from your toad instead of a push. If you will only be using it every so often might be worth the trouble. It's not like the toad is pulling the whole weoght just helping to get it going. Once i actually get mine going in the revs it feels pretty strong.
hmmm...?
Who be playing the busnuts?
happy coaching!
buswarrior
23% + bus = no fun at all ! :o Although you must have one hell of a view)
Ive got to say im getting a bit bummed hearing some of this, I really would want to get the bus up here if its at all possible. But I am a bit hard headed and dont take no for an answer real easy. So I have some more thoughts and have attempted to apply some math to the problem. This comes about from another discussion with a guy trying to get an MCI up an even steeper and longer driveway in NC with a switchback in the middle!
I have a power curve chart for an 8-71 272 HP which shows torque to be about 760 lb ft at 1000 rpm. 4107 has an overdrive bevel gear at .808, a 4.28:1 first gear reduction, and a 4.125 final drive. I dont know what torque would be available at lower rpm, but can possibly extrapolate 700 lb ft at 800 rpm from looking at the graph. 11-20R tires show to be about 41.5 inches tall, for a radius of 1.72 feet. So I assume roughly 700 lb ft of torque from 800 - 1000 rpm. The bevel gears drops torque to 565 lb ft, first gear multiplies it 4.28 times to 2420 lb ft, the final drive multiplies it 4.125 times to 9985 lb ft at the axles. Divided by a 1.72 tire radius, this puts 5805 lb of force to the tire treads, providing they dont lose traction. Of course this all assumes the motor is producing rated power.
On an 18% grade with the bus weighing 28000 (I'm pushing the numbers up for the worst case), I would have to provide (28000 x 18%) 5040 pounds of force to keep the bus from moving downhill. With 5800 pounds of traction it should keep moving upward if its already doing so. If my weight is lower I will have even more acceleration. If the engine speeds up it makes more torque, I will have even more acceleration.
Obviously this is marginal performance, and I dont know what the bus rigged out will weigh. You guys pegged it pretty close that it might not be possible, and the math shows it is truly marginal. So now to ask what other options are possible. I do NOT want an automatic. Is it possible to change the bevel gear to the earlier 1:1 ratio? Obviously the bus would be lower geared, but I would get an impressive jump in torque into the gearbox. That 5800 pounds of traction goes up to almost 7200 pounds with a 1:1 bevel. With that much tractive force the 23% part of the grade shouldnt even slow me down. (28000 x 23% = 6440). It wouldnt have the much top end but it would sure climb hills!
I am well aware the bumper is fastened to the engine carriage, and would certainly strengthen it well before attempting to push it too hard, and the tow bar is well strong enough. I would hope that anyone pulling a load behind a bus (or anything for that matter) would have their hitch built to withstand the stress of pulling whatever they hook to it. Hitches should be rated higher than whats hooked to them, in all three axis. IOW, the hitch on the bus should be capable of withstanding forces in excess of the load. In any case, a 3800 pound jeep would never be able to muster more than its weight in traction, and on this grade I doubt it could provide more than 3000 pounds traction, and so could probably only provide a push of 500 to 1000 pounds to the bumper. That would probably be all id need to make it, but I would be much happier if the bus could pull its own weight up.
With the above figures, your startability would be 21.7%-not enough to maintain a 23% grade-sorry. Good Luck, TomC
Art, one of the reasons that you will find trouble trying to get peak mileage out of the Detroit two stroke is because they are not very efficient at light loads.
I have tried a full tank of fuel running 55 on I5 along the west coast; I got 9 mpg. We typically get right near 10 mpg running 60 to 65. However, when the speed is picked up to 73, our mileage only drops to 9.5 mpg.
A couple of times, we fought some serious headwinds, and I thought that the mileage would be really be bad, but it wasn't. When we went exploring in King's Canyon, driving anywhere from 35 to 50 and climbing and dropping thousands of feet, we got 8.5 mpg.
Driving slow, a four stroke could have done a lot better than our two stroke, but the efficiency while heavily loaded is probably close to a lot of four strokes. This is one of the reasons that you see repeated references about slamming the door on your hand before driving one of these old girls. Being shy with the throttle doesn't get you a whole lot.
However, if you can get it to the point that it is usually working just hard enough, you get pretty good results.
Our coach is a stock 4106 weighing in at a bit over 27,000 lbs. We climb a number of grades at 20% and a bit over. I believe that our coach would climb the driveway that you describe.
To do this, I would get the clutch out all the way as soon as possible at the bottom of the grade and floor the throttle as the speed came up to 15 miles per hour and I would keep it floored against the governor until the grade leveled out. If it didn't pick up enough speed before it hit the steep part of the grade, I would stop and creep back down.
If you don't have DD3s or spring brakes, I would not consider climbing the grade at all. If you messed up and stalled on the grade, the engine could start up backwards; it couldn't help you slow down while backing down the grade. A hand brake alone would not be safe.
Your mileage may vary. Use the above information with care.
Good luck!
Tom Caffrey
Tom
I dont need to start out on a grade, I would start my run on almost level ground. I have about 40 or 50 feet to accelerate, then it increases to 18% in a bus length. It holds at 185 for about 70 feet where it then increases to 23% for about another 40 feet. Then it immediately drops to 11%. I may be able to rework the entrance to get more of a run, but probably the best I can hope for is another 40 or 50 feet of run before the grade starts.
How fast can a bus like this accelerate in 50 feet on level ground? If it can make 10 mph dont you think id have enough momentum and power to get it up over that hump?
A far more radical alternative is to reslope the entire driveway, then it would be about 14% all the way. But the magnitude of work would be enormous.
Possible to put a two speed axle in one of these? What about the 4104 bevel gears? Does the 5 speed spicer have a lower first gear? Is there a lower (higher numerically) axle ratio? Any other possibilities??
Quote from: pvcces on August 25, 2010, 10:48:26 PM
If you don't have DD3s or spring brakes, I would not consider climbing the grade at all. If you messed up and stalled on the grade, the engine could start up backwards; it couldn't help you slow down while backing down the grade. A hand brake alone would not be safe.
Your mileage may vary. Use the above information with care.
Good luck!
Tom Caffrey
Now there is a fun thought, full throttle reverse backing down a steep driveway.
Artvonne,
The only thing you left out in your equation, is a 15% drivetrain loss for a typical manual transmission. Your 5800 lb tractive effort has just gone down to 5220 lbs :( The 23% part would definitely be very difficult! This is assuming you're at sea level; if you're high up, it only gets worse...
Is your Jeep a 4.0L? If so, it should make enough power to spin all 4 tires in 4Lo. Tires have around .9 coefficient in the radial direction, so 3000 lbs sound about right. But I'm confused how you got a 500 - 1000 lbs net thrust? Wouldn't 3000 subtract (3700 x 23%) be arund 2200 lbs?
Regarding a 5 speed Spicer, I'm not too sure what GM uses, but the 5 spd Spicer in my Prevost has a 6.1 (or 6.6 maybe) 1st gear. As a result, there're rarely any hills my bus can't climb.
Another solution is to change out the tall tires to a low profile 22.5, such as 275/70, which is 38" compared to 42.5" for a 11r20 tire (same as 12r22.5). Nets you roughly 11% increase in thrust, but that 23% section would still be hairy!
Art -
11.00x20 tires are scarce as hen's teeth nowadays - that's a tube-style tire from before the popularity of radials.
11R22.5, 12R22.5, 11R24.5, 295/75R22.5, and 315/80R22.5 are the most common full-size coach tires being utilized now. You should be using one of these sizes for your number crunching, not the older one.
Not sure if you're using the overall gear ratio for your calculations. Here's the breakdown for the 4106/7/8 Spicer manual:
4.28 x 0.808 x 4.125 = 14.265:1 in first gear
2.50 x 0.808 x 4.125 = 8.332:1 in second gear
1.50 x 0.808 x 4.125 = 4.999:1 in third gear
1.00 x 0.808 x 4.125 = 3.333:1 in fourth gear
Punch those into your calculator and see what you come up with.
Back to GMC coach powertrain history:
Up until the 4106 was released for sale in the early spring of 1961, all of GMC's highway buses had been powered by the workhorse in-line 6-71 (the exception being the Scenicruiser). With this powerplant, the configuration was engine, clutch, transmission, bevel gears, drive shaft, rear axle. This is the combination that used the 1:1 bevel gearset, as found in the 4104s
During development of the 4106, it was discovered that the increased torque available from the 8V71 engine was blowing out the bevel gearsets after going thru the gearbox first. GM's solution was to reconfigure the powertrain. So, starting with the 4106, all coaches now had the powertrain laid out by engine, clutch, bevel gearset, transmission, drive shaft and rear axle.
Shifting the bevel gears ahead of the transmission cured the problem, and the powertrain became extremely dependable - still is. The increased power also allowed GM to slightly overdrive the gearbox by using the 0.808 ratio for the bevels, which yielded a coach which got nearly the same fuel economy as the older 4104s at 60 mph on the burgeoning Interstate system, at a lower rpm for better longevity, and more hp (by all of 37 hp) to help climb Rocky Top.
So, to use the 1:1 bevels, you need a 4104. Turbocharge the straight six, and you might make it up your driveway, but not with a naturally-aspirated model. Too much torque, and you'll blow out the bevels, just like the factory did during development.
Resloping the driveway to 14% might be an enormous challenge, but probably a lot cheaper than several clutch rebuilds?
The 5-speed Spicer does not fit in the V-drive configuration, sadly. I'd be first in line to get one if it did!
Two-speed axles are also not available for the V-drive, never have been.
You could put a 4905 rear axle pumpkin in the 4107 (Fast Fred's 4106 has this). They have a 4.375:1 ratio, but you'd take about a 5 - 6% hit on your fuel mileage.
You could also put a transit rear end under it. Most of those are 5:36:1, which gives you a top speed of 60 mph @ 2150 rpm. 4 -5 mpg, too!
It's all a compromise!
FWIW & HTH. . .
;)
Do you really need to start from a standstill or are you turning from a highway onto your drive with the clutch already fully engaged? You should be able to make the turn at or near the same speed as your Bounder. Even if it is only 5mph it would be a big improvement over a dead standstill.
How well does the Bounder climb your drive?
Are we talking paved or something else?
As has been repeated you will never really know until you try it. If the '07 is local see if the owner will give it a go. :)
Good luck
Don 4107
Quote from: artvonne on August 25, 2010, 10:54:59 PM
Tom
I dont need to start out on a grade, I would start my run on almost level ground. I have about 40 or 50 feet to accelerate, then it increases to 18% in a bus length. It holds at 185 for about 70 feet where it then increases to 23% for about another 40 feet. Then it immediately drops to 11%. I may be able to rework the entrance to get more of a run, but probably the best I can hope for is another 40 or 50 feet of run before the grade starts.
All the start ability figures were for starting from a dead stop, something my bus sucks at worse than a 4107. But given the description you give I think I could get my bus up that lane. Sounds like you have a decent run at that hill. First time up I would still suggest a decent tow vehicle on the high side, not attached but there to help if you run out of steam. Also as others noted a either have spring brakes (a must as far as I'm concerned....and anyhow 4107 must modern enough that they have spring brakes) or a very well adjusted handbrake. BTW if the brakes are poorly adjusted (slacks) your spring brakes will not hold you anyhow, so as usual care must be taken to make sure your 25,000+ toy is safe.
Quote from: RoyJ on August 25, 2010, 11:43:19 PM
Artvonne,
The only thing you left out in your equation, is a 15% drivetrain loss for a typical manual transmission. Your 5800 lb tractive effort has just gone down to 5220 lbs .
I dont believe there is any loss of torque through a drivetrain such as there is with horsepower. Ive been asking that question for over 20 years and always get the same answers, no loss of torque. But that could be wrong information, or, my assumption would be some loss at higher speed. In first gear and under 10 mph, the gear box and axle are turning so slow I doubt any loss would be significant. But again, its a grey area that tends to minimise performance.
Yes, the jeep is a 4.0, plenty of power.
I believe were at a point here where no one is really going to know for sure until I try it, and its going to be marginal in any case. There do appear to be some options to give it a boost, smaller tires, lower axle gears, but not much else. Which leaves either giving it a push or pull, resloping the drive, getting more run, or boosting power. Or combinations of all of these. Another option I thought of last night was a winch. Many big trucks around here, especially power company trucks, have big winches and live front axles. Big brutes that WILL get where they need to go. Once I'm up over the hump I dont believe I will have any trouble. I would only need to pull it up about 175 feet to have it sitting on the 11% grade up to the house, and the more I think about it this is probably the cheapest, simplest and safest option. That leaves the bus in more stock condition to preserve fuel economy, and saves me a butt load of construction work on the driveway.
Just to paint a better picture for everyone, im in northwest Arkansas back in the Ozarks, and it is VERY hilly and rocky. I dont know if its possible to change the slope of the drive, it could be solid rock underneath. And I would have to start digging before I would know! Currently I have cement on the steep section starting from the highway, hard pack gravel/clay from then on up after it levels off to 11%.
To be honest, the picture of the bus running backwards in reverse, pushing the jeep down the driveway and not being able to stop is a vey scary thought. Its easy to say it wouldnt happen, im sure id shove the clutch in before I stalled the engine, but I am pushing the bus to the limits of its capability. So until I have confidence it could make it up all by itself, the winch idea is what I will focus on. lets just forget all about getting up the grade and move on to converting it. I am picturing it up here at the house now.
how about some sort of winch system at the top of the hill... could prob be had for a reasonable $...old wrecker body/ winch ?..just need a massive front end attachment built into the bus and please stand back as the cable can cut people in half ! ahhh typing at the same time ! it would make coming and going a big deal......... could have the hook up also on the back so you are always safe.........s..........
RJ
Thank you for all the information and history, it is appreciated. I forgot the 11/20s were tube types, and I was just looking at some on our pumper truck yesterday. I want to run whatever tires are most readily available at most truck stops. It is as you say, all about compromise.
As I posted above, I am going to completely forget about trying to modify the bus to make it up the grade. If it cant do it thats okay. However, I hope the discussion wasnt completely rediculous and that it offered something to someone. I am interested in the idea of the 4905 differential however, but not to get it up my drive. While most of my travels will be flatland, I do have to get out of the Ozarks first and there are a lot of steep grades between here and there. For example, there are 94 turns between here and town with many steep grades between 7-10%. And maybe I want to go deeper into the Ozarks where there are even longer grades, lower gearing would a great help. The loss in fuel economy you mention if using that final drive, would that dissapear if you kept the speed down, or do you think it would be a wash regardless?
note , we drive up a 17% grade on our driveway....I can hit the bottom only at about 8 mph because of a tree and a turn, I can make it up but have also failed to make the hill 3 times.wer'e in a mci 7 w/8/71 turbo allison 4 speed and a "combo" rear end (GMC scenic rear)..... right at 20 tons.........s.......
So lets talk HVAC. My thoughts are to use the factory A/C condensor on the side of the bus, and rip out everything else associated with it that is no longer needed. I would plumb heat runs under the floor to wherever the HVAC unit is located. My idea is to use a conventional residential 240 volt compressor and A-coil, probably a ton to ton and a half compressor. For heat I am considering in floor radiant hot water, using a gas (propane) water heater, with engine and DHW loops. I could also run a heater core with the A coil and have hot water forced air heat for backup and on the road, using engine heat.
For power I have a 6.5KW diesel for standby,and would use inverters and batteries off the engine alternator on the road. Basically I think it would all be AC power except the fridge. My feeling is the generator is quite derated from what its capable of, but until I can have someone who knows about them look it over I wont know.
The generator is an Onan liquid cooled 3 cyclinder diesel, but the engine is Kubota. What little ive found on the web it looks like the whole unit is probably Kubota and Onan just painted it green and put thier name on it. The same engine (D950) powers other generators rated at 10KW. Its currently wired for 120 volt, but I will rewire it for 240 with split legs. Its a 12 wire gen.
No that is a Onan head and you will find that engine is built for Onan it will be a little different than most Kubota engines same with their gas units Robin builds those just for Onan and in most cases the HP setting on the engine dictates the KW of the generator and heads, the same head can have different KW's just needs hp to achieve the goal
good luck
Quote from: steve wardwell on August 26, 2010, 07:30:32 AM
how about some sort of winch system at the top of the hill... could prob be had for a reasonable .........
Great minds think alike? Yes typing same time, lol.
Quote from: luvrbus on August 26, 2010, 09:16:24 AM
No that is a Onan head and you will find that engine is built for Onan it will be a little different than most Kubota engines, the same head can have different KW's just needs hp to achieve the goal
good luck
Seems they put a lot of these same generators into motorhomes through the 90's, but there is very little information about them. Ive been trying to find out if the higher output generators (7.5KW, 8.0KW, etc..) used a different head, or if the lower output ones (mine is a 6.5KW) are simply the same head but derated. Calls to Cummins/Onan have not produced any help. I dont even know whats its surge rating is.
What I have learned is that output changes with heat, altitude and humidity. The gen is currently residing in the bounder behind the front wheel, in an enclosed cabinet, and its probably a bit starved for air where its located. And the cabinet is small, and so is the radiator. Perhaps it could be uprated a bit if it was mounted in a place with more airflow and a larger radiator??
Quote from: Don4107 on August 26, 2010, 12:10:13 AM
How well does the Bounder climb your drive?
Are we talking paved or something else?
Good luck
Don 4107
The Bounder is very slow to build power for some reason. Ive looked into a bit but have decided to just make it go away rather than put more money into it. If I get on it at the bottom, the turbo is still not spooled up when the grade starts, and I stall to a stop momentarily right on the 18% part of the grade. But if I keep my foot down it starts to boost and gets moving again. By the time ive reached the steepest part I am having to throttle back because im going to fast.
The steepest part of the drive is concrete. From there on the rest is hard clay and gravel
Hello Artvonne,
Where in the Ozarks are you located? I am SW of Harrison and can show you the grades I pull with my 4104, I am not sure of the percent grade but I pull Gaither Mountain OK but I do have a run at it, If you are close maybe I could take a look at your drive or you could look at mine? As for over the 2 lane roads here in the hills I usually run the 4104 in 3rd gear here close to home, normally the only time I get to 4th is between here and Branson or going south to Little Rock.
Rick
Im 10 miles west of Clifty on Hwy 12, about 15 miles NW of Hindsville, about 20 miles and 94 turns east of Rogers, about 2 miles from War Eagle Mill. And I would love to see your 4104. To be blunt, I would probably choose a 4104 if I thought it would work for me. Its just that those ginormous cargo bays and flat floor of the 4107 have me mesmerised. Maybe all I need is a reality check?
Art -Quote from: artvonne on August 26, 2010, 07:51:30 AM
The loss in fuel economy you mention if using that (4905) final drive, would that disappear if you kept the speed down, or do you think it would be a wash regardless?
With the 4.375:1 rear end, you'll be running 100 rpm higher
all the time compared to the stock 4.125:1, regardless of terrain. So, you'll burn more fuel. Simple.
The Ozarks and Appalachians are speed bumps compared to what we have out here on the West Coast, btw, and we did just fine with the OEM powertrain. . . Just think of Aesop's Fable of the Tortoise and the Hare.
Quote from: artvonne on August 26, 2010, 11:35:40 AM
If I get on it at the bottom, the turbo is still not spooled up when the grade starts, and I stall to a stop momentarily right on the 18% part of the grade.
Try this: At the bottom of the grade, hold the Bounder still with your left foot on the service brakes. Floor the throttle till the turbo spools up, THEN let go and see if she "bounds" up your driveway.
Quote from: artvonne on August 26, 2010, 03:17:40 PM
Its just that those ginormous cargo bays and flat floor of the 4107 have me mesmerised.
Actually, the floor of the 4104/4106 is flat front-to-rear, compared to the stadium seating arrangement in the Buffalos, literally giving you more living space. The wheelwell intrustions are only about 2" high, easily covered with furniture up front. Lots of different ideas in the rear, from twin beds against the walls to a slightly raised floor have all been done.
As I said before, you can level the front floor of a Buffalo, but if you're over 5'10", you'll bang your forehead on the Vista Windows framing. And you still end up with less interior space.
I agree that the huge baggage bins, plus the pantograph doors, are a big plus for a Buffalo, especially the 4905s. No other coach comes close, including a lot of the new 45-footers (w/ the exception of BK's new S-417 Setras).
OTOH, since you've said numerous times you want to "build it light", those enormous bays could work to your disadvantage, because you'd be tempted to carry a lot more "stuff", which equals weight. . .
Quote from: artvonne on August 26, 2010, 03:17:40 PM
Maybe all I need is a reality check?
Yup! ;D
FWIW & HTH. . .
;)
PS: Suggest you start a new thread for the HVAC stuff, rather than having it get lost in this one.
Quote from: artvonne on August 26, 2010, 07:04:15 AM
I dont believe there is any loss of torque through a drivetrain such as there is with horsepower. Ive been asking that question for over 20 years and always get the same answers, no loss of torque. But that could be wrong information, or, my assumption would be some loss at higher speed. In first gear and under 10 mph, the gear box and axle are turning so slow I doubt any loss would be significant. But again, its a grey area that tends to minimise performance.
Yes, the jeep is a 4.0, plenty of power.
Not showing off here, but just so you know my background, I'm a Mechanical Engineer.
The hp formula is: rpm x torque / 5252. If there's no loss in torque, how can there be loss in hp?
The primary loss of a transmission is friction of the gear mesh process. The amount of torque lost is proportional to the torque input to the transmission. In other words, 15 lb-ft loss with 100 lb-ft input, and 45 lb-ft of loss with 300 lb-ft input.
Because the primary loss of a transmission is frictional, rather than viscous, its loss is therefore the same regardless of rpm or vehicle speed. In fact, 1st gear would have the MOST losses, due the the greater difference in gear diameters. Like wise, direct drive has the least losses. You can even measure the stall torque at the wheel, and it'll be the same 15% (or even higher, as static friction is higher) as if the bus were rolling.
Roy -Great info!
Quick question:
Quote from: RoyJ on August 26, 2010, 06:11:55 PM
In other words, 15 lb-ft loss with 100 lb-ft input, and 45 lb-ft of loss with 300 lb-ft input.
This is an example of the proportional loss, correct?
Not the actual loss we poor GMC folk suffer from with our convoluted V-drive layouts?
TIA!
;)
Artvonne,
You are just a little over an hour from me, I am just off Ar Hwy 43 between Harrison and Compton. If you want to see my 4104 my cell is eight-seven-zero-4-1-6-sixty-4- twenty. If you want to come over give me a shout and we can get together on a day and best time.
Rick
are you tempted to try that driveway ? (bring a camera) lol I just might to see this.....sorry sorry sorry.......You know my wife has never gone up our little hill with me? by the way her eyes can sure get real big when i do this crap lol
Quote from: steve wardwell on August 26, 2010, 06:55:28 PM
are you tempted to try that driveway ? (bring a camera) lol
And a nice beefy tractor.
p.s. make sure you have lots of memory and batteries for the camera...I'm thinking youtube.
Based on RJ's 14.265 overall gear ratio in 1st, the maximum 760lb/ft torque (with 60 injectors), and 485 rpm 12R-22.5 rubber weighing 28,000lbs, your gradeability (not startability) will be 17.5%. If you turbocharged the engine like mine is with 1125lb/ft torque your in motion gradeability rises to almost 26%. Torque makes a big difference. Good Luck, TomC
Quote from: RJ on August 26, 2010, 06:21:36 PM
Roy -
Great info!
Quick question:
Quote from: RoyJ on August 26, 2010, 06:11:55 PM
In other words, 15 lb-ft loss with 100 lb-ft input, and 45 lb-ft of loss with 300 lb-ft input.
This is an example of the proportional loss, correct?
Not the actual loss we poor GMC folk suffer from with our convoluted V-drive layouts?
TIA!
;)
Yeah that was purely an example. Reason being the typical counter-argument:
If a 300hp engine looses 30hp with a certain transmission, and you hook that same transmission to a 600 hp engine, wouldn't it also loose 30hp?
Now I don't know much about the V-drives, but if I understand correctly, that's another set of gears (to change engine rotation orientation) in addition to the gear box and diff? If so, then 15% loss would definitely be quite possible!
Roy -Quote from: RoyJ on August 26, 2010, 08:41:17 PM
Now I don't know much about the V-drives, but if I understand correctly, that's another set of gears (to change engine rotation orientation) in addition to the gear box and diff? If so, then 15% loss would definitely be quite possible!
Perhaps this will help you visualize the GMC V-Drive. It is "flopped" from the actual orientation, but you'll get the idea. (I actually got it oriented correctly in my photo editing software, but you couldn't read the notations!) In your mind, "roll" the engine assembly over the rear axle so that the transmission bevel gear is in the lower RH corner, and you'll have the proper layout.
Quote from: RoyJ on August 26, 2010, 06:11:55 PM
The hp formula is: rpm x torque / 5252. If there's no loss in torque, how can there be loss in hp?
That formula is too simplistic really. First of all, that is only refering to brake HP at the crank. To find road HP at the wheels the device would have to be tested at the output end and compare this with power tested at the input end. Whether that would prove loss of torque through friction, or only a drop in HP is a very deep subject. So many of the greatest minds have attempted to explain it, so many times, that the entire subject is filled with controversy and error.
I do recall an engineering professors explaination quite clearly. If you apply torque to the crankshaft pulley nut, and measure torque at the output end, is there any loss due to friction? No, there is only the division or multiplication of the gearing ratios. Of course, that is in a static environment, not dynamic, and as you say, this creates other forces.
In any case we can see that its ability to make an 18% grade is borderline. I found the discussion quite enlightening, and I hope everyone else did as well.
Artvonee
come to NC and try my 04. It would have no trouble with your drive way.
uncle ned
Quote from: artvonne on August 27, 2010, 08:25:49 AM
Quote from: RoyJ on August 26, 2010, 06:11:55 PM
The hp formula is: rpm x torque / 5252. If there's no loss in torque, how can there be loss in hp?
That formula is too simplistic really. First of all, that is only refering to brake HP at the crank. To find road HP at the wheels the device would have to be tested at the output end and compare this with power tested at the input end. Whether that would prove loss of torque through friction, or only a drop in HP is a very deep subject. So many of the greatest minds have attempted to explain it, so many times, that the entire subject is filled with controversy and error.
I do recall an engineering professors explaination quite clearly. If you apply torque to the crankshaft pulley nut, and measure torque at the output end, is there any loss due to friction? No, there is only the division or multiplication of the gearing ratios. Of course, that is in a static environment, not dynamic, and as you say, this creates other forces.
First, no, that equation does not just apply to the crankshaft, or any specific power plant. It's based on the simple physics formula: power = force x velocity.
hp = 33000 foot pound / min = 33000 foot pound radians / min = 5252 foot pound rpm. Remember, 2pi radians is one rev, and 33000/2/3.14 is roughly 5252.
So, knowing this equation applies to ANY moving system, look at the terms. hp = tq * rpm / constant. Fix rpm and the constant, if tq doesn't change, how does hp? How can you possibly have a transmission that looses hp, but miraculous, keeps a constant tq?
Regarding your professor's example, I hope he made a genuine mistake, or else he shouldn't be teaching. Static friction is the greatest of all, this is why it's hard to get a car rolling, but much easier to keep it rolling. Likewise, it's much harder to get a gearbox (under torque transmission) rotating, than it is to keep it in rotation.
Picture this, if a box sitting on the ground has 50 lbs of friction, and you push it with 30 lbs, it won't move. Every body can picture this. But this is what gets confusing: if you push it with 100 lbs, and your friend is holding it on the other side from moving, what does he feel?
A) 100 lbs?
B) 50 lbs?
B) is correct.
Instead of you and the box, picture an engine and transmission. If you put 500 lb-ft into a transmission, and the net loss is 50 lb-ft, then the output shaft only feels 450 lb-ft, even if the bus is sitting still!!!
It's intuitive to think that under static conditions, a gearbox transmitt 100% torque, but it doesn't, it transmissits even lower. The gear teeth experience even more friction when they're sitting still.
double post
I have really enjoyed this thread. :)
Anyone who has a chance to try to turn the shafts in a transmission by hand knows it takes some doing to make it spin. There's some gear meshing losses to be sure.
A friend had a roadranger case carved open, gears sets intact, as a display for teaching drivers, with a handle for spinning it.
Drivers weren't as rough, once they could see the internals moving, how the gears changed, and which bits they would be risking breaking through careless use.
But, it was a bear to get all those gear sets to spin.
happy coaching!
buswarrior
Quote from: RJ on August 27, 2010, 01:55:58 AM
Roy -
Perhaps this will help you visualize the GMC V-Drive. It is "flopped" from the actual orientation, but you'll get the idea. (I actually got it oriented correctly in my photo editing software, but you couldn't read the notations!) In your mind, "roll" the engine assembly over the rear axle so that the transmission bevel gear is in the lower RH corner, and you'll have the proper layout.
Thanks for the info RJ. That's one crazy looking setup for sure! Clever way of packaging though.
This will definitely increase torque/power loss over a regular transmission; it has two extra bevel gears.
The typical rule is, you can make a driveshaft as long as you want, and you'll loose zero power, whether static or moving. Same applies for u-joints near zero angle. The reason is, a drive shaft has no moving components, and therefore, cannot dissipate any power, except for the minute amount of elastic deformation of metal.
As soon as you put a bevel gear, straight gear, or pulley, it becomes a moving system. Gears have to mesh, and rubber belts have to constantly roll along a metal ridge, both of which create rolling friction. And again, since static friction > rolling friction, the greatest torque loss of a moving system occurs at zero rpm / velocity.
Lets just agree to disagree on torque loss, Ive read too many books by engineers that contradict each other I dont know if anyone really knows. Even automotive manufactures disagree on HP measurements and how to accurately measure it.
I drove down and met Rick and his wife and family yesterday and checked out his Bus. It was an absolutely beautiful day through very beautiful country, that was only surpassed by the breathtaking view from Ricks own back yard of the Buffalo river valley. I thought I had a pretty place. For those who havnt been through the Ozarks and the Buffalo river, its really worth the trip. Ive been through most of the US and just cant think of anywhere prettier.
Rick showed me around his Bus, and not having been around any Bus in over 20 years, I had forgotten how nice 4104's could be. Then he took me for a ride up the road a ways and back, and boy am I hooked. He has a real nice rig anyone should be proud of.
And now im all confused. I really had my heart set on a 4107, followed by a 4106, but tooling around in Rick's 59 '04 really made me seriously rethink things. Engine offers more access, uses less fuel, systems a bit simpler. And it sounds from researching them they have better pulling power down low while still being able to reach freeway speeds. Certainly not 85 like an '06, but plenty fast enough. And maybe someone can answer what a standard 4104 should have for speeds in gears? Rick says 3rd is good for 55 or so, which seems high to me? How would a 4104 be for finding parts to keep it going?
Pretty sure a '04 has worse pulling down low than a '06. Actually I'm hard pressed to think of any bus I've read about that has worse "startabilty". I had to rock mine out of it's wheel ruts when I picked it up, it had traction put not enough guts to climb out. Mine may be worse than most though...it's the only '04 I've driven. But I really like my bus, and the engine access is awesome. Pulled my starter, "rebuilt" it and reinstalled in aprox 2 hrs and that was the first time I had done it and I was in a shopping center parking lot using road tools. Problem with the starter, open the engine bay and engage it by hand (also works well when the batts are low as you don't waste current on the solenoide/bendix thing). Parts availabilty seems good enough 'xcept they get turned in for scrap so much. I think I remember that GM made more '04s than any other bus so that's good. Problem area for me is all the vdrive stuff is on a different angle than for the rest of the GM highway coaches and the tranny is very specific....good thing is the tranny seems pretty tough. Brakes are cool too as you can fit springs brakes from any truck stop on it (unlike '06 and possibly others). The flat floor front to back is nice and there is the fact that an all original 4104 is a good looking bus.
Art -
Pulled up my spec sheet on the 4104.
Bevel gear ratio = 1:1, located AFTER the transmission
First = 3.86:1
2nd = 2.50:1
3rd = 1.50:1
4th = 1:1
Two final drive ratios were available: 4.125:1 (stock) & 3:55:1 (optional, and VERY rare)
Forgot to look at the torque spec, but the 4-valve 6-71 puts out 238 hp @ 2100 rpm. Can be boosted to 275 hp w/ a turbocharger. Not uncommon to also set engine up for 2300 or 2400 rpm, they will survive.
No automatic available, unless you repower with a transit donor, must change rear axle, too (pumpkin's on the wrong side of the coach centerline for repowers).
TomC should have the torque specs for both NA and Turbo 6-71s, and can supply the gradeability.
5065 was the total number of 4104s built from 1953 thru 1960. Early models had a generator, late production have alternators. Originally 12V POSITIVE ground, most survivors have been converted to negative ground.
Good, solid, dependable workhorse. Better built, too, than a 4107 or 4106. More rivets, more aluminum, thicker skin.
Rear window glass is now made from unobtainium.
Front windshields, door, and driver's window glass is the same as all later production GM highway coaches. (Scenic is different.)
One has to consider the time frame within which this coach was designed and built. The Interstate system didn't exist till near the end of production. Most highways were two-lane rural roads, on which 60 mph was considered "fast." Simpler time, simpler machine, designed and built accordingly.
Understanding that time frame, and the related performance, equals enjoyable ownership.
Definitely The Tortoise from Aesop's Fable.
FWIW & HTH. . .
;)
Has anyone around here looked at the 4107 in Cocoa Beach Florida? His fuzzy pictures have been on and off of craigslist for over a year now, andwhen I spoke to him a year ago he wasnt willing to send any more or better pics. I dont know if it would be worth looking at if he went down to $2500., its a long was for me to go to look at a dog.
http://ocala.craigslist.org/rvs/1912449845.html (http://ocala.craigslist.org/rvs/1912449845.html)
Rick gave me a heads up, and I went to look at a 4106 conversion that popped up on craigslist yesterday over in Fayetteville. I am probably not the best person to rate it, but hes a bit high IMHO. Its a bit rougher than it looks in the pictures. Bags settle within a few minutes, add on electrical needs sorting, plumbing not real well engineered, but "works". Seems to start run and go down the road okay, but he wouldnt let me drive it so I cant comment on feel of controls. It has power assisted steering. OTR AC condensor and compressor are gone, gas tank for portable type 5500 watt gen in compressor bay. Gen cant power AC,s without tripping 20A breaker on gen.
http://fayar.craigslist.org/rvs/1925654535.html (http://fayar.craigslist.org/rvs/1925654535.html)
I have talked to the guy in Cocoa. The first time he seemed like the bus was in ok condition and only needed cleaned up. We were planning to drive down and look at it and called him back, but something didnt seem right. The ad has changed many times and new pictures keep popping up. I knew he had the ability to take pictures and wouldn't so I didn't waste 2 days driving to look at. I have the feeling he is hiding something.
When figuring startability with a manual transmission, the engine does not produce full torque with clutch engagement. Most all engine manufacturers will list clutch engagement torque rating on their engine. For instance, the Series 60 produces 1650lb/ft torque, but makes 1000lb/ft torque at 900rpm for clutch engagement. This is what startability is based on.
Figuring that a 6-71N with N65 injectors puts out 228hp (real horsepower) and 600lb/ft torque, this means that the engine probably puts out maybe as much as 400lb/ft torque for clutch engagement. The 6-71T with N80 injectors could put out 300hp and 900lb/ft torque, and probably puts 550lb/ft torque for startability.
If we use the bus weighing in at 28,000lbs and the 3.86 low with 4.125 rear axle ratio and 485rpm 12R-22.5 tires, that works out to be-10.3% startability with the 6-71 natural and 14% startability with the turbocharged 6-71. Not good-I've seen 4104's just about burn up the clutch trying to bump over a curb. Just for emergency use, lets say that you are slipping the clutch to get it into its' torque range near 1500rpm. The maximum startability on the natural engine (with full 600lb/ft torque) will be 15.4% and the turbocharged engine will be 23.2%.
Now lets intall a V730 into these buses and see how this changes with the same 4.125 rear end. With the Allison automatic, the full torque of the engine can be used plus the 2.5 torque multiplication (on the V730, 2.0 on other Allisons). 1.77 first gear. The 6-71 natural will have a startability of 17.7% and the turbocharged will have 26.6% startability.
For those that would like to fool around with startability-here's the formula. First take the total weight of your rig and multiply it by 10.7 and put that figure into memory. Then take the starting torque of the engine for a manual-or the full torque of the engine for Allison X Torque converter ratio if you have an Allison (2.5 for V730, 2.0 for all others) X first gear ratio X rear end ratio X tire revs per mile (actual). Divide that by the figure in memory and that is your startability percent grade. Good Luck, TomC
Quote from: smokedetector on August 31, 2010, 08:19:01 AM
I knew he had the ability to take pictures and wouldn't so I didn't waste 2 days driving to look at. I have the feeling he is hiding something.
Thinking the same .