4107 thoughts

[RJ]

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. . .

[Don4107]

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

[zubzub]

 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.

[artvonne]

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.
 

[artvonne]

  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.

[steve wardwell]

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..........

[artvonne]

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?

[steve wardwell]

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.......

[artvonne]

  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.

[luvrbus]

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

[artvonne]

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.

[artvonne]

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??

[artvonne]

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

[Rick59-4104]

 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

[artvonne]

  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?