C3 (69) Rear differential codes

[Rob M.]

Hi all,

A couple of days I removed my rear spring. I'm now trying to determine if my cover is an original. In the tech. judging manual code is refered to determine the ratio and application. I can't seem to figure out where to find this code.

On the differential cover I only find a casting number and GM7. No ratio code, production date or plant suffix letter. Where should I locate these numbers exacly?




The C3 Weblog

[Steve Wallach]

Re: C3 (69) Rear differential codes

The code and date of assembly should be stamped into the lower edge of the case, NOT the cover. Look at the very bottom edge of the case where the cover
mounts to the case.

Hope that helps,

Steve

[Rob M.]

Re: C3 (69) Rear differential codes

Hi Steve,

Is it visible after removing the spring? And is there a way to determine if my cover is still original (number?)?

greetings,
Rob.

[Steve Wallach]

Re: C3 (69) Rear differential codes

No way to know for sure if the cover is the same one that was installed at the factory, you can tell if it is a "correct" cover. The Covers doe not have any numbers that would connect it to any particular car. The "case" however, has the assembly stamp and a casting date. You should be able to see the stamp with the spring on or removed if the car is on a lift or you can crawl under the car? You may need a flash light and some brake cleaner. The stamping may be full of grease? You should get the book "The 69 Stingray" By Rick Bizzoco,
it is a GREAT resource with lots of pictures.

Cheers,

Steve

[Rob M.]

Re: C3 (69) Rear differential codes

Hi Steve,

Just crawled under the car again (which is in a nearby garage) and cleaned the case ridge and found 1AU 92568W. Using the manual this should translate to 3.36:1 Warner Gear Posi build on Sept. 25 68 (build date of the car is 9/30/1968) so things look like they are on order. I can't place the first 1 though...

The cover reads 3871375 as casting nr but this isn't reflected in the judging manual. I expect it to be correct as well but it would be nice if someone could confirm...

thanks for your help,
Rob.

[Steve Wallach]

Re: C3 (69) Rear differential codes

Hi Rob, from memory the cover part number sounds correct.
Yes, the build date is right for your car. I'm not sure what the "1" means, but someone should chime in here. Do you have a 68 Judging manual? That may clear up what the 1 is in reference to?

Regards,

Steve

[Steve Wallach]

Re: C3 (69) Rear differential codes

My case stamp starts with a 2 then AF, I know I have a Heavy Duty Posi Rear End. Mine is a 4 spd. and Mine is a 68 assembled in January of 68.

Steve

[Marc R.]

Re: C3 (69) Rear differential codes

I believe the 1 indicates the first shift.

[John H.]

Re: C3 (69) Rear differential codes

"AU" is a big-block 3.36 Posi, and the "W" is for Chevrolet-Warren, where the diff was assembled; the "1" is for first shift.

[Chas Henderson #28127]

Cover code

Rob,

If you look at your cover, over by the filler plug, the area between the two cover mounting-to-the case holes, you should see a letter and 3 numbers that were cast, with the last number being the year. That should at least let you know if the cover is close to the date of the assy. There may even be a cast date on the housing itself. I just put mine back on the car so I can't look for it right now to double check.

Chasman