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Old 10-04-2016, 02:28 PM   #1
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Trying to identify my rear axle ratio, help?

Hello everyone, I just purchased a 1990 Chevrolet shorty with a Detroit Diesel 8.2. I am trying to identify my rear axle ratio so i can calculate if my motor's governor has been turned down. I've crawled all under and around the back end of the bus, but the stamped ID tag has been coated with bus undercoating and is unreadable. I have copied all of the casting numbers off the rear end, but i don't know if that will help identify the axle. It has some weird bolt with a set nut sticking out of the drivers side of the chunk so i my ridiculously hopeful side It may be a 2 speed axle and its just set to the lowest ratio and the switch gear was never hooked up. I doubt it though. So... if there is anyone that thinks they can identify the axle ratio based on the casting numbers here we go...

Eaton Axle:
210316e with a NF and a DI above it, this is on the third member on the drivers side front.

210339 , this is up by the input shaft, where the driveshaft hooks to the universal joint.

A210340 Not real sure where this one was

01300 Again, not sure where this one is located

and on the only readable riveted plate is stamped with nothing else readable:

PT NO 05989 (maybe)
HSG Model
HSG Cap
HSG ID NO


Good Luck:
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Old 10-04-2016, 05:26 PM   #2
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Look like this?


First hit when googling "1990 chevrolet school bus eaton axle":

GMC School Bus REAR AXLE/EATON
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Old 10-04-2016, 05:42 PM   #3
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No, thats not it. Where that flat plate thing is on the 3rd member there is a large bolt, like 1" in diameter with what looks like a locking nut that sticks out perpendicular to the driveshaft (parallel to the axle tube) this nut is hollow, it may have some actuator or connectors inside of it but its all full of goo so i don't really know.
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Old 10-04-2016, 05:45 PM   #4
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Location: North carolina
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Year: 1986
Coachwork: Thomas
Chassis: Ford
Engine: Detroit 8.2
Rated Cap: 60 bodies
On my 86 eaton rear data plate with the pt.no and msg model..
The numbers are stamped into the plate so maybe you can pull it of and read it from the back side?
The other data plate which tells the model,and the gear ratio is in line with the drive shaft on top. Not quite on the very top but in between the drive shaft and the axle housing. And those numbers are raised lettering so if you can find it maybe you can pull it and do the same
I will try to look at my casting numbers when I get a chance and see if anything matches.
Sorry I can't help with the governor adjustments? Maybe if the weather not bad I can go see an old diesel mechanic friend of mine and ask? I have been trying to find time to take my bus to see him anyway.
Good luck
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Old 10-05-2016, 09:45 AM   #5
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Link posted will take you to more information.

If it looks almost like the picture above, sounds like you have a 2 speed axle minus the actuator, I don't know that for sure, but sure seems like it.
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Old 01-17-2017, 08:42 AM   #6
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Join Date: Jul 2016
Location: Prince George, BC, Canada
Posts: 275
Year: 1974
Coachwork: Blue bird
Chassis: CHEVROLET C60
Engine: 350 ci on propane
Rated Cap: 48
According to my buses build sheet I have a chev 350, an Allison at545, Rear axle is 7.20:1, tires are 10 R20.5 How fast is it running @ 4000 rpm?

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Old 01-17-2017, 08:51 AM   #7
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im going on the assumption of a standard truck tire height of 41". and youd be able to do close to 65 .. your At545. may limit that if your redline is 4000 as it's converter will slip and allow the revs to go up under load..

if I knew the exact tire height we can calculate it easier...

https://www.ringpinion.com/calculators/Calc_RPM.aspx

-Christopher
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Old 01-17-2017, 09:08 AM   #8
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Year: 1998
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what if the R&P or entire center section has been replaced ?
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Old 01-17-2017, 09:24 AM   #9
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Join Date: Jul 2016
Location: Prince George, BC, Canada
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Year: 1974
Coachwork: Blue bird
Chassis: CHEVROLET C60
Engine: 350 ci on propane
Rated Cap: 48
Quote:
Originally Posted by cadillackid View Post
im going on the assumption of a standard truck tire height of 41". and youd be able to do close to 65 .. your At545. may limit that if your redline is 4000 as it's converter will slip and allow the revs to go up under load..

if I knew the exact tire height we can calculate it easier...

https://www.ringpinion.com/calculators/Calc_RPM.aspx

-Christopher
My mistake my tires are 8.25 R 20 and roughly 37" diameter. I was not home when I asked.

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I'm worried that I might have done damage driving home last fall. Driving some mountain down hills at over 65 mph.
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