Here is the deal I have 3 GSL SE's. I know that the driveshafts from 79-82 are the same, then 83-85(manual), and then you have the 84-85(auto). I also know that the 83-85 U-joints are staked in and non-serviceable.

I want to have one built or buy one for my SE that is serviceable. Recently I picked up a shaft for free, that has C-clips on the inside of the U-joints, but has a smaller differential flange.

My question is what models have the different size flanges and did the slip-yokes vary between models as well as the shaft lengths?

Does anyone have the specs? I want to know if I could use this drive-shaft and just source out a new rear flange?

 

the smaller flanged driveshafts are serviceable and are for the 79-82 model years. the 83-85's have a larger rear flange and are not serviceable. mazdatrix sells a serviceable driveshaft for the 83-85's. all shaft lengths were the same other than the one for the auto trans. that shaft is shorter in length.

 

So is the rear flange the only difference between the 79-82 and 83-85 or are the slip-yokes different as well?

If they yokes are the same, one would think you could find a large flange to install on an 79-82 driveshaft. Then you would have a 83-85 serviceable driveshaft.

 

The 83-85 u-joints can be made to be servicable on the stacked u-joints. I just had it done on my 1985 GSL. Code me $100 but I'm sure it can be done cheaper. Heres a pic. I went ahead and powdercoated mine. This is what I used. The driveshaft shop had them in-stock.

u-joint part numbetr 430-10A IIRC http://www.rockforddriveline.com/replacem.htm

 

Another question, can you take a small pinion flange and install it onto a large pinion flange rearend(SE)? Anyone know if the spline counts are different? I would assume I'm not the first person to think of this.

 

I have just been researching this and it seems you can (READ entire post) swap them. The actual pinion shaft (aside from gear ratios) and the seal are the same for 79-85 according to parts listings.
I have been searching and "I could find" only one post by sgt FOx in this thread to confirm it, https://www.rx7club.com/1st-gen-arch...n-info-871075/
However,
There are numerous posts by others stating you have adjust the pinion/differential if you remove the nut that retains the flange. The Haynes manual describes replacing the diff oil seal (which includes removing the flange) without an adjustment other than torquing the retaining nut while allowing the rear wheels to spin and stopping the wheels with your foot for a final torque of 94 ft. lbs. The FSM only describes complete differential tear down and reassembly with "adjustments". I think that is where the numerous warnings from everyone come from. I don't fully trust the Haynes manual. I would like know for sure, so if someone knowledgeable in this area could chime in...