We have a 84 rx-7 GS with a 12a in it (its my gf's). The back end went out when she was driving it over a year ago, since then it has been sitting at a junkyard where they were unable to find replacement parts. We would like to trailer the car home and fix it up, but we have a few questions that we were hoping someone could help us with.

I have not had a chance to look at the problem(s) myself yet, so I can't say firsthand what all is wrong with it. But I do know that the pumpkin is bad and needs to be replaced, and possibly the rear axle as well(so basically the drivetrain rear end).

We are starting our parts search, and we have a few questions. First, are the 81-85 (any model, i.e., GS, GSL, GSL-SE) pumpkins and rear axle interchangeable with a GS? Second, does the engine make a difference? In other words, can we use a 13b pumpkin/rear axle on a 12a engine(will it hook up to the drive shaft?) If anyone could help us out/offer advice on this, that would be great. Thanks, Nate

 

84-85 parts are a direct swap. Internally and externally. 83's are a combo of 81-82 and the 83-84. If you swap anything other than the 83-85, you will need the drive shaft.

Try to find the 84-85 rear end with disc brakes, they have the lsd. If you can't find that, then the 83 or 81-82 with the driveshaft. Engine does not matter, but there is a difference in the gear ratios between the 12a and 13b.

 

The best is the '84/85 13b rear. Gives you the biggest disc brakes and the LSD...
Otherwise, get an '81/82 rear with discs (make sure you get a driveshaft with it); it has an LSD and the driveshaft has replaceable U-joints
Failing that, as trochoid said, the 12A from '84-85 with discs is still a nice upgrade, and again has the LSD.



The rear end gear is not a big difference... I wouldn't worry about it too much.

 

Only an 84 or 85 Pumpkin will swap in. they changed to Larger Axles in 84 so the eariler years do not work. You can use a 12A or 13B one. The 13b will have a 4.10 Gear and LSD where yours is a 3.90 and non LSD. The 12A should be easy to find. Hit the parts section and someone there can easyly get you what you need. I thing Midwest7 (member here) is in KC and he parts out cars some. Bet he could help you out easy.

IF you what to change out the full Rear then the info from the other two guys hold true.

 

I hate to rain on you but...