Hi! Well, now that I've gotten started, I might as well make a nuisance of myself! Can anyone tell me where I can find the interpretation of the Parts ID Codes on a paper sheet glued inside of the glove compartment box? This is on my '94 G20. I need to find the code for the differential. Chilton says; "Just check the code in the glove box". That sheet has 72 different sets of 3 character codes and 9 other misc. code sets! Is a code guide available somewhere (preferrably online) or is that info privy only to dealerships? Thanks! Bob

For RPM codes make your gm parts dealer your best buddy.
Or have the run you vin no.

The rear sometimes has a tag on back cover.
But the rear end gears could have been changed .
The best and true way to find the gear ratio is to remove inspection plate and check the ring gear for ratio or count the pinion and ring gear teeth and divide ring gear teeth by pion teeth.
MT

Thanks for the info MT. I crawled under & checked the dimensions of the unit and found two sets of numbers on the backplate: "08 06" and "26007927". Naturally, I can't interpret either of these to be a gear ratio. I also found a number on the housing -- "5822" -- which may just be the housing part number. Is there any place online where I could get the ratio from these numbers or the VIN? I'll be looking for a differential through our local salvage yards as it wouldn't be worthwhile to put in a new one. The van, having appx 175,000 miles on it, appears to be worth about $700, and maybe two hundred with a bad rear-end. Since the engine and body are in such good shape, combined with the fact that I've put around 2 grand into suspension, brakes, shocks, exhaust, etc. in the past year, I felt I'd rather try to get it back on the road for us. We're raising a severly handicapped little boy & transport him & all his equipment around daily. That equipment doesn't fit very well into our Montana, but with the Chevy there's room to spare. Bob

The tag is not much help there.
Google a search on GM RPO codes.
here is one hit.
http://www.angelfire.com/ny2/96transam/rpocodes.html

rear end codes start with a G---

Thanks a MILLION MT! With your "hints" and my rpo codes, I found the exact info I need ("3.42:1")! Should be relatively easy to find a replacement now. TX Again! Bob:)

You are welcome and thanks for letting us know you got it figured out.
Good luck.
MT