Click on image for the lowdown. 
====
| | | Forums66 Topics128,056 Posts1,055,803 Members48,426 | | Most Online14,466
Apr 26th, 2026 | | AD Chevy Trucks  Over 6,000 pictures Brad Allen has an awesome collection of Chevrolet factory pictures that he has set up from film strips. Check them out!
Lots of work on Brad's part ... pure enjoyment (and references) for you!
| | THANKS!
For helping keep this great
old truck web site
on the Internet for over 30 years! and not clogged down
with Ads!  Again, thanks!
| | | | Joined: Sep 2008 Posts: 59 Wrench Fetcher | | Wrench Fetcher Joined: Sep 2008 Posts: 59 | Hello all, I found a 1972 GMC school bus with the 6 lug big bud pattern axle in it, single speed. Does anyone have a range of possible gear ratio's for it? I would like to get an idea if it will work before I ask the junkyard owner if I can pull the cover on it. | | | | | Joined: May 2005 Posts: 8,878 . | | . Joined: May 2005 Posts: 8,878 | 4.xx-7.xx is a start, but I expect you wanted a narrower range? It's probably pretty slow.
Often the ratio is stamped on the front end of the pinion shaft, you don't have to disassemble anything.
It would probably be easier to jack up one wheel and count turns to figure the ratio than it would be to remove the cover and deal with the oil.
Grigg
| | | | | Joined: Sep 2008 Posts: 59 Wrench Fetcher | | Wrench Fetcher Joined: Sep 2008 Posts: 59 | No, that is good - I did not know if 4 something was a possibility. I will check the pinion shaft on Friday. The axle is 250 complete so if it is a 4 or low 5 something, I will be in business.
I was going to swap a NV4500 into my 57 but I sold the NV4500 after figuring it was more work that I wanted to do and there were people who wanted them way more than I did.
The easiest way to get the RPM down is throught the axle swap I think and being 6 lug budd pattern, many school buses are fair game for swap material.
I have a disc brake Ford dana 80 10 lug but with no good 22.5 wheel options, I am not ready to use it.
Ryan | | | | | Joined: May 2005 Posts: 8,878 . | | . Joined: May 2005 Posts: 8,878 | 4.something may or may not be a possibility for that axle model (whatever it is), but without knowing the axle model the 4-7 something pretty much covers the possibilities.
You really can't learn anything from our guesses, you'll just have to see what it really is.
Now if it was an older axle we could probably narrow the choices, but a newer axle like that could have a whole range of ratio choices.
Grigg | | | | | Joined: Feb 2004 Posts: 29,773 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,773 | If you opt to jack up one wheel and count driveshaft turns, remember that the spider gears will double wheel speed. For instance, if it takes 2 1/2 turns of the driveshaft to get one wheel rotation, the axle ratio is actually 5:1. Be sure and double the number of driveshaft turns to figure the actual ring & pinion ratio, or keep turning the driveshaft until you get two turns of the wheel.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: Dec 2008 Posts: 11 New Guy | | New Guy Joined: Dec 2008 Posts: 11 | The Dana 80 would be a good choice.
The F$%d dana 80 should have 37spline axles and 4.88s in it, and you can also get 19.5s for it to
What kind of wheel/tire combo do you want anyway?
60 Apache 4X4 235
67 C20 292
90 Dodge W250 Cummins
| | | | | Joined: Sep 2008 Posts: 59 Wrench Fetcher | | Wrench Fetcher Joined: Sep 2008 Posts: 59 | Thanks, guys. I agree the dana 80 would be good but I just bought new 22.5 rubber and had my wheels reconditioned so I would like to keep those wheels and tires on the truck and limit axles to those with readily available 22.5 wheels, 6 lug bud pattern preferred. | | | | | Joined: May 2005 Posts: 8,878 . | | . Joined: May 2005 Posts: 8,878 | Some reasonably new trucks still run 6 lug Budd wheels. I see a number of UPS and FedEx trucks with them and 22.5 tires, also some school busses.
If that first axle does not have a desirable ratio keep looking, you'll find a newer one that does, and probably with better brakes and easy to get parts.
Grigg | | |
|
|
