I have a 2.78 R&P that was given to me a few years ago. Neither me or the guy I got it from recall what year Cutlass it came out of. I'd like to install it in a 70 Cutlass that has a 2.56 open in it now (reusing the original carrier).

The pinion is stamped:

14A39 GM CD 394701 93

The ring gear has 7/16 RH threads and is stamped:

14A39 GM ZD 92

Obviously the 14A39 is the tooth count...do the rest of the numbers/codes mean anything? My assumption is that these gears should fit the original carrier with no issues, but I recall reading that in '70 the ring gear bolts changed to LH thread..is that right? I didn't get the bolts with the 2.78, so if i can't reuse the bolts from the 2.56 I just want to know up front so I can have all the parts on hand before I start taking things apart.

 

Hi Don
For the work/expense of changing gears I don't think the 2.56 to 2.78 will feel like a significant difference from behind the wheel. If you want a little more zip I'd be looking more at say a 3.23 or even 3.42 if the drop in gas milage isn't real important to you. Just a thought, John

 

Yes,the 70 O-axle changed to LH threads for the ring gear bolts.67-69 had RH threads.I have some correct RH thread bolts for your 2:78's,if you end up needing them. $5.00 would be plenty.