Rear Diff ID

[doza59]

I have a stock 1976 02 . originally delivered to the Bay Area California and produced April 1976 per my Vin #. 

Would I have a 3.90 :1 diff ratio or 3.64 ? 

Thanks 

Doza

 

 

[Conserv]

And It would have a 3.64 differential if it is a ‘76 California version. There were originally both California emissions controls (a thermal reactor exhaust manifold) and emissions controls underhood stickers that would verify it is a California version.

 

Only the ‘76 49-state cars received 3.90 differentials.

 

But differentials have often been swapped over 42 years. Counting the ring and pinion teeth is a dependable way to verify the ratio, although the ratio and manufacturing date were stamped onto the housing.

 

Regards,

 

Steve

 

Edited September 7, 2018 by Conserv

[halboyles]

22 minutes ago, Conserv said:

It would have a 3.64 differential if it is a ‘76 California version

 

You can verify this by looking at the numbers stamped on the driver's side of the differential.  You might have to use a wire brush to clean the area off.  I understand that most US '02s had this gear ratio from the factory.  40/11=3.64.

Edited September 7, 2018 by halboyles

[Conserv]

14 hours ago, halboyles said:

 

You verify this by looking at the numbers stamped on the driver's side of the differential.  You might have to use a wire brush to clean the area off.  I understand that most US '02s had this gear ratio from the factory.

 

+1

 

And if the differential isn’t too dirty, or too rusty, the differential will reveal its manufacturing date as well as original ratio.

 

Here’s the original 3.90 from my ‘76 49-state version. The differential housing was cast March 24, 1976 (“24376”), as shown in the first photo below.

 

The pinion has 10 teeth and the ring gear has 39 teeth (“10     39”), yielding a ratio of 3.90. And the differential was assembled in April 1976 (“4” over “6”). Both sets of numbers are shown in the second photo. My ‘76 was manufactured on April 23, 1976.

 

Regards,

 

Steve

 

Edited September 7, 2018 by Conserv

[Son of Marty]

After all these years to only way to tell for sure is to pull the back cover and count the teeth and look at the spool, taking my 74's case markings you would think it's a open 3.64 diff where if you pulled the cover you'd find a Motorsport 75% 3.90 in there, although to be fair if you drove it you'd suspect it had a lsd.?  

[ray_]

45 minutes ago, Conserv said:

 

+1

 

And if the differential isn’t too dirty, or too rusty, the differential will reveal its manufacturing date as well as original ratio.

 

Here’s the original 3.90 from my ‘76 49-state version. The differential housing was cast March 24, 1976 (“24376”), as shown in the first photo below.

 

The pinion has 10 teeth and the ring gear has 39 teeth (“10     39”), yielding a ratio of 3.90. And the differential was assembled in April 1976 (“4” over “6”). Both sets of numbers are shown in the second photo.

 

Regards,

 

Steve

 

Do you have similar pics for the front diff?

 

 

/me ducks