HELLO,
I CALLED MCI TODAY TO FIND OUT WHAT GEAR RATIO I HAVE FOR MY 1975 (AUG) 5B. I COULDN'T BELIEVE THE TECH
COULDN'T ANSWER THE QUESTION ON WHAT IT HAS IN IT. HE DID GIVE ME SOME NUMBERS THAT IT WAS BUILT WITH.
THE NUMBERS LISTED BELOW.
R 164-WX27
491408
THE QUESTION I HAVE DOES ANYONE KNOW WHAT THESE ARE? HE DID ASK IF IT WAS BUILT FOR THE MOUNTIANS OR
FLATS? I REPLIED, HOW WOULD I KNOW!
THANKS FOR ANY HELP,
STEVE 5B....
Who did you talk with at MCI, Steve? I might have some tips for you...I have learned a thing or two...lol.
God bless,
John
Have you gotten under your bus and looked at any of the tags on the rearend? Generally there is one on the housing itself and that might have the ratio of the original drop-in, but there may be a tag on the drop-in itself and that would be far better.
Worst case scenario you could look at the end of the pinion (after you clean-up all that dried grease and crap) and look at the numbers there.
Of course, there will be real bus guys here in a minute that can help you out too!
Steve, there are a couple of things you can do to determine your ratio, if MCI can't help you. Also recall that someone may have changed the rear end since it left the factory.
If you have the typical bus size tire (~~ 490 revolutions per mile), you can get a feeling with the tach. If you are doing about 70-72 at 2100 rpm, you probably have a 3.73. You can factor from there to get other rear end ratios.
The other way is to jack the bus up and rotate BOTH rear tires one complete revolution (make sure that both go 1 revolution so that your spider gears don't mess with the results) and count how many times the drive shaft rotates. It is a two man job, but it will be darn accurate. Usual cautions, as you will have to release the parking brake -- be sure to block the bus!
I don't know about MCIs, but the typical Eagle rear ends are 3.73 and 3.36. Since you have a 5 with a drop box, I would think it might be the same.
Jim
The book for my 68 5A says 3.36:1 is standard and 3.7:1 is optional. Since your 5C is 7 years newer it may be different. Do you have the maintenance manual? That is where my info is from, in the section for the rear axle, first couple of sentences. :)
JOHN,
I WAS PUT ON HOLD FOREVER, I THINK THE TECH NAME WAS JOHN. I DID HOWEVER SPEEK WITH SEVERAL.
STEVE 5B.....
My spec books call for 3:36 for the 8v71 with a manual transmission and 3:73 for 6v71 with a Allison 740 only 2 gears they show
good luck
JIM,
LIKE THE FORMENTIONED WEATHER IS THE FACTOR NOW. THAT IS GOOD TO KNOW
STEVE 5B...
I remember spinning a wheel to get my rear end ratio. It's been a while, but I only remember having to jack one side. Have I gone senior?
HEY ED,
THE MANUAL, I HAVE IS FOR ONE SEVERAL YEARS OLDER PROBABLY THE SAME AS YOURS. IT NOWS HAS AN 8V-92 N.
WOULD THIS REQUIRE TO CHANGE THE REAR END?
STEVE 5B......
LUVRBUS,
IS THAT RATIO FOR THE INTERSTATES OR THE MOUNTIANS LIKE THE TECH ASK?
STEVE 5B....
Lin, you can use just one wheel. However, you will have to divide the number of drive shaft revolutions by 2, as the spider gears will mess with the count.
Jim
Is someone shouting?
Sorry but I don't know the answer,but the ratio of 3:73 for the 6v71 and Allison makes sense to me I doubt a 6v71 would have enough power to leave a 7/11 with 3:36 gear.
If you have a tach and tell us what rpms at what speeds it is a no brainier or tell us your top end speed if around 80mph you have a 3:36
good luck
Okay, Steve. Here is what I would suggest. Try calling back and speaking with either Jim Mclean, Jim Salsbury, or Terry (I am not sure how they spell their names). Ask them if you can get the build sheet for your bus (the original build material sheet for your bus). One of those guys should be able to help, because if you have your build sheet, you know what the original rearend was.
God bless,
John
With 12R22.5 tires (486rpm), the 3.73 will have a top speed of 70, and the 3.36 will have a top speed of 78 at 2100rpm. Good Luck, TomC
TomC,
Thanks for that info!
Steve 5B.....
Steve,
Jim and Lin are right, I remember doing it a few times with one wheel jacked.
I thought I divided by two but I think Jim is right, it is probably X2. It is for sure one or the other!
Mark the shaft with chalk and count the turns. If you do the math wrong it will be very obvious!!
Steve, just a thought but with your 8V-92 natural you may want a lower cruising rpm than I would with my 8V-71. My 5C has the 3.73 gear and I top out at about 72 mph by my watch and the mile posts. That seems fine for me, it gives me a bit better performance in lower gears than otherwise. You might do better with the 3.36 if you happen to have it.
Brian
Our MC-8 with 8V71 & 740 transmission has a 3.73 rear end ratio. I recently had a 102A3 at my place that had the 8V92 & 740 that had the 3.36 (or 3.33), I forget which. After driving both of them it seemed that our MC-8 had as good or better acceleration, but the 102A3 definately ran fast faster and cruised at a lower RPM for a given speed. This was simply seat of the pants feels like testing, no stopwatches or timers were used for this test. YMMV Jack
Gus, when I wrote the note about drive shaft rotation being twice with one wheel rotating, I sat a long time and tried to recall which way it was. So, maybe we should play it safe and say it will be off by a factor of two. How is that for "engineer speak" ;D
Jim
Hmmmm, my 5A has an 8V71 and Allison 644 and 3.36 gears and 11r 22.5 tires. My speedo only reads to 80 mph and i know that it reads 3mph fast. I have had it pegged at 80 running at about 1850 rpm in 4th and still had throttle to spare. After i let off of the pedal it took 6-7 seconds to drop below 80 mph. I have never hit top end. Would sure like to find a place where i could find out without getting a ticket! ;D
I am not touching this one Ed
good luck
1850 rpm on 11R22.5 tires with a 3.36 diff is 62.8 mph. Perhaps your speedo starts to read high at higher speeds?
1850/3.36 is 550.6 axle rev. per minute or 33,036 axle rev per hour.
11R22.5 loaded diameter is 38.4", circumference is 120.576", or near enough 10 feet. (Bridgestone data page)
10 feet divided by 5280 is 0.0019 miles per revolution
0.0019 MPR times 33,036 RPH is 62.76 MPH
EDIT: I said 38.4 loaded diameter, when what I really meant was 19.2 loaded radius, times two, to fit into the PI D formula for circumference. Obviously it's not the actual loaded diameter, since a loaded tire is only flat on the bottom...
If you have the electric sensor speedo on the front brake drum, the sensor is too close to the drum and it's reading the bolts twice at high speeds. I had that problem too. But anyway, the math is the math...
Brian
i have checked it with gps, and road mileage test areas with stop watch, and at 75 mph on the speedo i am actually doing 72.
No problem with that, Ed, but then you aren't running 1850 rpm, or you aren't on 11R-22.5 tires, or you don't have a 3.36 diff ratio, or your gearbox is overdrive (which is perfectly possible, I suppose...). Other than that it's pure math and math is math, there's only one way to do it. ;)
Edit: So, for fun and because it's bus related and therefore more interesting than work, I calculated that at 80 mph, 1850 rpm and 3.36 diff ratio you could have a .78 overdrive 4th gear, or you could have 48.9" tall tires. I am still working on the HP required to get a bus going at 80 mph, but I am pretty sure an 8V71 would have enough to do it, no wind and on the flat.
Edit again: My bus tops out on the governor at 72 mph, near as I can tell, and with 12R22.5 tires (Firestone FS560 with rated 19.8 loaded radius) and 3.73 diff that is 2280 rpm. But I don't have a tach...
Brian
Brian, My tach appears to be fine, it reads where it should at idle and fast idle, and when i accelerate, it does not jump around but climbs smoothly. 4th gear is 1.00, my tires are 11r 22.5 and are 41" in diameter. The tag on my rear end says i have the 3.36 gears. Going down the road last year i had my wife write down the following; In 4th gear @ 65 mph,-1700 rpm, 55psi oil and 180 degrees H2O temp. In 4th gear,@ 55 mph, 1500 rpm. I don't like to run it in 4th at 55 because it is lugging at 1500 rpm and will downshift itself at 1450-1480 rpm. Also i need to be turning 1700 rpms or my temp will start going up. If you look back to Jan 26-09 at the Re MC5 Fuel Economy post, you will see that Viento1 said that he had to feather the throttle on his old 5 to stay below 80. Also Steve5B posted that he got a ticket in Indiana for doing 104 in a 70 mph speed zone in his 5. "Math is Math"........ yes, it is. And math also tells us that neither the bumble bee or a helicopter is capable of flight but they both do. ;D I don't know what my top speed is, because i have never reached it yet, but i do know that it is not 68 mph. :)
I'll stop now, I know when I'm beat... I guess numbers add up differently wherever you are...
Brian ???
Sometimes numbers don't tell the whole story. Many times i have seen that what looks good on paper doesn't work in the field. ;)
Ed, the numbers never lie. They are what they are. Gauges lie, watches lie, GPS systems lie, all sorts of things lie, but numbers do not. People can and do interpret what the numbers may say wrong, but I don't think I am doing so in this case.
I challenge you to come up with a formula or calculation that backs your observed data. Show me how it can happen, then I'd agree with you. Easier yet, just show me where I made the mistake in my calculation. Since I've taken the step of checking my data with a known accurate professional spreadsheet designed to calculate exactly this sort of thing, I'll be surprised if there is a mistake.
Just for fun, how many engine rpm would it take to do 104 mph in a MC-5B, with either of the two stock gear ratio's that seemed to be available?
Brian
Removed
Jim,
Whichever way it is if it is done wrong it will be pretty obvious!!
I'm pretty sure it is rev/2 because I remember being surprised at how fast that drive shaft turned when I turned the wheel.
Brian, i am not saying that you are wrong or made a mistake. Algebra is not my strong suit so no formulas from me. :) All i am saying is what i have experienced. Now if it was just me, i would be wondering if i just imagined it, but i am not that senile......yet! ;D And since two other people with 5's have also done it and one has proof in the form of a ticket, you can see why i have to question a statement that says that X mph is all that is possible and you can not go faster than that. Bus races!!!!! we need to find a big long track somewhere that we can test buses on! ;D
What is the gear ratio of the drop box ??? them number must be included in the numbers game ;D
Just to chirp in, if my bus could do 100 mph I would gladly take the ticket and frame it and put it on the wall for everyone to see. LOL
drop box ratio on an MC-5 is 1:1.
You can bring a horse to the water, but you can't make him drink...
It is really hard to determine tire rotation per mile just by measuring or using measurements from the manufacturer. Different tires have different deflections. A 11R-22.5 can have RPM's (revs per mile) of 497 to 505. The best is to get the exact tire and go to your tire manufacturer to get the rpms of that tire. For example- a tire my seem to get 1850rpm at 62mph with 3.33, but using the 500rpm (which is most common), the actual engine speed at 62mph is 1720rpm-a difference of 130rpm! Good Luck, TomC
I thought I would chime in...
i have the Mc5 with the 8v71 and the alison 644. 12r22.5 tires. I am not sure what my ratio is. I just got back from a 48 hour trip and my top speed is about 75mph at 2400rpm (I must have the 3.71 gears?)
rpm guage a little bouncy
Speed on guage not gps.
my old mc5 with the spicer and no rpm guage would run in excess of 80mph - I never did find the top speed but there was lots of peddle left :)
75mph @ 2,400rpm with 12r-22.5 tires (486rpm) makes for a 3.95 ratio. So either your speedo is off or your tach is off. But your close enough to say you have the 3.73 ratio. Good Luck, Tomc
Just a quick update on this. A couple of days ago we were on I-40 headed east out of Flagstaff. The speed limit is 75. As is the case almost everywhere people were going a lot faster. :) I got out the gps and checked my speed. I knew my speedo runs 3-4 mph fast as verified by, 1. my wife clocking me in our car. 2. going past many roadside radar units that are there to let you know your speed when entering a construction zone. 3. Freeway mileage test areas. And 4. By my gps. All say the same, actually the gps was the most precise, it said my speedo was reading 3.8 mph fast. Sooooooo, i ran the bus up until i hit 80.1 mph. I was in 4th gear with my MT 644 and i was turning 1900 -1950 rpm. Still had throttle to spare. Sorry Brian, but i didn't want to get a ticket so i did not try to find out what my top speed is. Plus we were towing our jeep too. ;D
Ed, do you want to sell your drop box I'll even do the change out I believe you one of the rare .93 ratios from Rockwell
good luck
Okay Brian, do the math again using the .93 and see how it turns out.......
Clifford, What did the .93 ratio units go in? Thanks Tom
Tom Y they were used in the Rolligons high flotation trucks back in the 60's and 70's before they went to the hydraulic drive.
They had a gear and yoke at the bottom where normanly it would bolt to 3rd member where the pinion gear was you just removed the bottom cover ,gear and the yoke and they would bolt up to differential on a Eagle or MCI 5.
It is a hard item to find but they are out there I found 2 in New Iberia La but the bull gears were missing and you can not buy that gear off the self now it has to be cut on special order for 4 grand .
good luck
Luvrbus, Thanks for the info. Tom
At Brewster's in the '70s, some of the MC5As went that fast. They had the 8V71 and 4 speed manual. Most of them only went 65 to 70 mph. I had one the summer of '75 that was like Ed's, I was scared to find out how fast...
JC
Clifford, I had posted somewhere that I had a great gear manufacturer who was willing to work with me (at least at the time) to cut the gears to make an overdrive for the drop box.
The issue I always struggled with were gear centers. I did not want to get into modifying the housing to change gear locations. At the time, I asked if anyone was willing to "lend" us a drop box to do an engineering study. Didn't get any offers, so I dropped the project.
If the box manufacturer did the design work, and if the center locations are the same, it would be real interesting to get one and see what it would take to replicate the parts.
Jim
Clifford, i think that i will just keep it no matter what it is. :) Bus races anyone? for pink slips? ;D
Jim, The only way to change ratios is to change centers. Or are the gears different sizes? I think the input and output are the same size?
Clifford, Do the trucks run the same input gear as the busses? Thanks Tom Y
Tom, there are three gears (input/idler/output). At first, I thought you might be able to change the number of teeth on the input and output gears and compensate with the idler gear. That would not make any sense if you consider the input would have to have more teeth (smaller idler gear) and that would not match with a smaller output gear. My next thought is that a person could look at other gear profiles that might make the gear centers work out, but I thought more about that today and it does not seem logical. Thus, a change in gear center would be required.
We have a person in the Eagle International Chapter that said he made an overdrive drop box. I will try to see what he did when I get some spare time.
I talked to Wayne ("Rusty") today and he has a spare drop box that we could play with. However, I don't have the time and it looks like an uphill battle.
The main reason for an overdrive gear box is probably to properly gear a bus when a four stroke conversion is done. However, that conversion suggests that a 35% plus overdrive is ideal for most applications. Thus a .93 does not do much. It is probably OK for a four stroke that wants a bit more speed. When I first started thinking about the overdrive concept, it was several years ago and both AutoShifts and World transmissions were priced sky high.
So, it looks like a whole drop box design would be required. Probably way too costly for our limited market.
BTW, I looked at the .93 gearing and that still does not explain Ed's speed capability if he has a 3.73 and 2100 RPM speed limit (~~ 77 MPH). If he had a 3.36 and .93, he could probably do 86. If he just had a 3.36 he could do about 80. All of this are rough calculations based on tires that have about 500 rev per mile.
Jim
Jim, I agree with your thinking. But with my setup the .93 may be just right. I to looked at the world tranny at the time. Way to pricey, now I would do it as the price has really come down. I have a good 740 so the .93 sounds good. Tom Y