C3 Differential Case & Cover Numbers Questions

[Paul C.]

How many different numbers/codes on the differential & cover? This is for a 1971.

1. Differential cover would have #3871375. This was used from approx 1964-1977. My casting date is A 17 8 but the car was built in January 1971. That doesn't seem to fit. How would you know if it had a "6" whether it was 66 or 76? Some earlier year had casting dates on some but not on others.

2. The differential also had a casting number---for 1971--it was #3899143. Was there also a casting date? If so where is it.

3. The number for the rear end gear ratio. Mine is hard to read but appears to be AA (3.55 gear); W; 341--day of the year (December 7), E--source, and 2--the assembly shift. Is there supposed to be a number which indicates the year it was made?

How close is the differential and/ differential cover date supposed to be to the car build date?

Did I miss any other numbers of the differential or cover?

[Gary R.]

Re: C3 Differential Case & Cover Numbers Questions

Hi Paul
While I usually don't go crazy over numbers when I work on something I can offer some info. Your cover would be Jan 17th either 1968 or 1978. So as you know it is not the original one. There is a casting code just like the cover on the lower Left corner of the housing, below the side axle. Sometimes the code is upside down or covered in rust scale/dirt. Then there are the stampings on the bottom of the housing. The assembly date usually is couple of months later.

[Alan S.]

Re: C3 Differential Case & Cover Numbers Questions

Hi Paul,
Here's a picture of the location of the casting date on the differential carrier that Gary described.
A 4 1, installed on a mid-January built car.
Regards,
Alan

[Paul C.]

Re: C3 Differential Case & Cover Numbers Questions

Alan:

Thank you for the pictures. Found the casting number on the differential housing--- H 11 0. August 11, 1970. Fits my Jan 28, 1971 build date. My car was undercoated and everything is covered up. What does the judging team score a car with undercoating? Looks like all I need is a new cast iron differential cover. That maybe difficult to find but I will try. again Thanks for the pictures.

[Alan S.]

Re: C3 Differential Case & Cover Numbers Questions

Hi Paul,
You may want to first search for "undercoating" to see some of the prior threads about undercoating and it's impact on judging of the chassis.
You might then also want to start a new thread with that title to get a sampling of peoples current thoughts on the impact on scoring.
Regards,
Alan