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Old 09-17-2006, 08:11 PM   #1 (permalink)
Seanb23
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So how DO you find out what gear ratio your rear axle has ?

I looked at the differential "pumpkin" and there is no tag that I can see on it. The rear end of my Short Bus is very heavy-duty...the 8 bolt kind, where you have to pull the axle out to do a brake job...I remember that from the last rear end I had like this one. These are "fully-floating" if memory serves.

The vehicle VIN code does not indicate what it came with, I think.

Any ideas ? Can you count the bolts on the pumpkin or look at other identifying characteristics to get an idea of what is in it or anything ?
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Old 09-17-2006, 08:22 PM   #2 (permalink)
High Sierra 2500
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You can often find the axle ratio on the inside of the glovebox door.

If you don't find it there you can jack the axle up, rotate the wheels one turn, and see how many turns the driveshaft makes.

Other than that the only way I know is to pull the differential cover and do a little gear tooth counting.
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Old 09-17-2006, 08:26 PM   #3 (permalink)
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Unfortunately, the printing on the panel with all that info is kind of rubbed smooth, blurry, and unreadable for the most part. It's on the inside of the driver's door where it closes...a very convenient location, except for the fact that it is always rubbing against your hands or whatever, over and over and over again through the years !!! Hahaha...oh, well...I thought there was some way you could look it up without jacking the thing up and such. Thanks...
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SOLD: 1987 Chevy Short Bus with J code NA 6.2l out of an 88 Suburban...over 8500 GVW, thus 3L80HD and Duallys on a 4.10 geared heavy duty rear axle. Custom loft/enclosure in the back where the seats were.

1992 Dodge 250 LE "Club Cab" with intercooled Cummins 6BT motor, Getrag 5 speed, and a "Reading" telephone truck style utility bed. Runs like a raped ape, but the body is a work in progress.
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Old 09-17-2006, 09:45 PM   #4 (permalink)
yachtcare
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Another short bus owner!

I'm working on one also. Was kinda baffeled about what type of rear gearing they would put in this thing. I figured it to be 4.11, but I pulled the diff cover (14 bolt corporate rear end), as I figured it is always good to change the rear end lube when you get a used vehicle anyway. If you look closely at the edge of the ring gear as you clean things up before the new lube, you'll see two numbers stamped in the edge of it, along with a date code. You divide those two numbers and that will give you the ratio. The numbers are the number of teeth on the ring gear and pinion gear. Mine turned out to be geared 3.73 with the G80 eaton limited slip.

Hope to see some pics of your project, and hear some of your ideas.
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Old 09-17-2006, 10:12 PM   #5 (permalink)
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Hi ,

3.73 with G80 awsome setup but dont abuse it .I blew mine 1 week after intaled a new cage in it "showing off" how good they are .


Now i do own another one and i treat it with respect and it serve me well.

Ed
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Old 09-17-2006, 11:30 PM   #6 (permalink)
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Quote:
Originally Posted by yachtcare;1305006;
I'm working on one also. Was kinda baffeled about what type of rear gearing they would put in this thing. I figured it to be 4.11, but I pulled the diff cover (14 bolt corporate rear end), as I figured it is always good to change the rear end lube when you get a used vehicle anyway. If you look closely at the edge of the ring gear as you clean things up before the new lube, you'll see two numbers stamped in the edge of it, along with a date code. You divide those two numbers and that will give you the ratio. The numbers are the number of teeth on the ring gear and pinion gear. Mine turned out to be geared 3.73 with the G80 eaton limited slip.

Hope to see some pics of your project, and hear some of your ideas.
Hey, thanks ! Yeah, that's exactly the kind of information I was looking for.

I'll get to that when I get back in town in a week, and post up some pictures of my project in the works. Basically, the back 2 rows of seats were removed by the previous owner, so I'm going to put an enclosed loft in there, bolting it to the walls of the vehicle. That way, it's a camper up top, and you have a secure place for all your tools and jacks or whatever underneath once you secure the rear door with better bolts and a good strong latch. I did this with my last van/bus, but it was on a regular Chevy van body, so there wasn't nearly as much room as there is in this one. This one is as wide and as tall as a regular school bus, but only as long as a van.

Of course, with all that wind drag, the much vaunted high mpg capabilities of the 6.2 are pretty much negated...I just calculated today that I am only getting 11mpg, same as I was with the (much shorter, lighter and narrower) van with a revved-up 350. Maybe this will improve slightly with a fuel filter change and some tweaking of the fuel system once I learn how to do that.

Yeah, used service vehicles like busses and ambulances can be a good deal. If they belonged to the government, there is a good chance that the important details like fluid changes and such were attended to religiously.
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SOLD: 1987 Chevy Short Bus with J code NA 6.2l out of an 88 Suburban...over 8500 GVW, thus 3L80HD and Duallys on a 4.10 geared heavy duty rear axle. Custom loft/enclosure in the back where the seats were.

1992 Dodge 250 LE "Club Cab" with intercooled Cummins 6BT motor, Getrag 5 speed, and a "Reading" telephone truck style utility bed. Runs like a raped ape, but the body is a work in progress.

Last edited by Seanb23; 09-18-2006 at 12:53 AM.
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Old 09-18-2006, 12:36 AM   #7 (permalink)
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To find out gear ratio without removing the cover: Jack up one rear wheel, mark the drum to backing plate with soap stone or equivilent, mark the pinion flange and housing. Turn the jacked up tire/wheel, 2 full revolutions using the marks to line up, while doing this, count the number of revolutions that the driveline makes and this will give you the ratio. Only available ratio's are: 3.23(vans only), 3.42, 3.73, 4.10, 4.56
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Old 09-18-2006, 08:24 AM   #8 (permalink)
High Sierra 2500
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Quote:
Of course, with all that wind drag, the much vaunted high mpg capabilities of the 6.2 are pretty much negated...I just calculated today that I am only getting 11mpg
Yeah, just think if you had a 350 in that thing... You'd probably be getting about 6 mpg...
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Old 09-18-2006, 08:57 AM   #9 (permalink)
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I was getting about 13mpg with mine, with the THM400. Mine sounds like it is more what you used to have, a standard width van, with 125" wb, and the high "bus" dome top on it. I'm in the process of swapping in a HD built 700R4, so hoping I can get the mpg up to around 15-16 range.
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Latest accquisition(1/18/08)...'94 Chevy crew cab dually 4X4 6.5TD "F"/4L80E, 4.10 gears, Snorklectomy, Vac pumpectomy, Warpspeed crossover, 3" downpipe, 3" straight pipe exhaust dumped ahead of rear wheels, Homemade TM, Faze boost gage, New 34583 FSD on huge heat sink in nostrils, Racor R20S(2 micron)fuel/water separator before lift pump, 2x0 battery cables/grounds, Pass side battery relocated to driver side .......more to come
HAVE 1970 GMC swb 1/2 ton getting a 6.2 now!

HAD 1968 Chevy C 10 swb 1/2 ton
1961 Chevy Apache 10
1990 Chevy RV on G chassis
1982 C 30 dually 6.2L "J" with sm465, Dana 70, 3.73 w Detroit locker
1988 G 30 Van (school bus) 6.2L "J" built 700R4
Proud Member #659 Dually Club
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