what does it take to to do the lsd and rear disc swap on a 79?

 

You need the whole rear end from a 81+ GSL model RX7...
Some notes below:
Well...the e-brake cables really suck in trying to get them off/on. I
have found no easy way to do that other than brute muscle and having
three hands. Make sure that you totally adjust the e-brake in the
drivers cockpit out so that it gives you a lot of slack in the cables.
There is a turn screw right by the handle and turning it out
(counter-clockwise) loosens the slack. You will have to readjust them
after installing them but that's the only way that I have found to do
them. Other than that the rear brakes are a snap.

Swap info:
Proportionaing valve: Up to you. I, personally, change them because I am paranoid and assume any problem will arise at a point where my life is at stake; not just tooling around town. However, I just checked the parts microfische and, at least from 81-83, the drum and disc proportioning valve part numbers were the same.

E-brakes: whoever said they suck apparantly did something wrong, as mine have always shown improvement, including the swap I did last weekend. The trick is to get one of the notches over the brake pad pin, as the e-brake rotates the cylinder to wedge the pad against the rotor...at least that's how I understand it to work. Also, if you don't align the pin and one of the notches, the cylinder will push only on the pin, causing very uneven wear of the pad and rotor. One other tip is that the longer of the two e-brake cables goes on the driver's (left) side.

Other notes: 81-82 pumpkins have the early companion flange pattern while the 83-85 pumpkins have the later companion flange pattern. Seems strange that they would change it in 83 and carry it forward, when the axle size change didn't come until 84. Anyway, the 81-82 LSD/disc rear ends require a 79-82 driveshaft and the 83+ rear ends require an 83+ driveshaft. Also note that the earlier "small axles" rear ends are actually stronger than the later "big axle" rear ends because the earlier housing is beefier. Not a big deal unless you are drag racing or running a turbo setup. You can also reinforce the housings, if necessary.

 

You can leave the drums and swap out the gears only and have the LSD with less work than doing the complete rear.

 

7aull: if you are going to use someone else's words, word-for-word, it would be nice for you to give credit where it is due. Tell people it is a quote and cite where it came from. In this case, the words are all mine, from the point where you said "swap info:" until the end of your post. Failing to mention the source make it look like you are taking credit for the information.

 

No you cant, the axles dont match. They explain this on mazdatrix also.

 

That's not necessarily true. There are three varieties of 1st gen rear ends: small axle with small flange (1979-82), small axle with big flange (83) and big axle with big flange (84-85). LSDs were available from 1981 through 1985, so ALL combos are available. Further, it's no big deal to swap the flange or driveshaft to make the large flange 83 work in a 79-82 car. To swap in an LSD pumpkin (the pumpkin-like gear carrier assembly), you only need to be sure to match the axle size. So, if you have a 79 RX-7, look for an 81-82 LSD pumpkin (or 83 LSD pumpkin with the 83 driveshaft). And, though it's not usually economically viable (~$200), you can buy small or large axle side gears to swap a big axle unit into a small axle setup, or vice versa.

FWIW, the small axles are ironically stronger than the big axle units. Why? The axle housings on the small unit are stronger, which prevents axle flexing under load; the most common cause of snapping axles. Obviously, you can reinforce either type of housing, so it's not that big of a deal. Just FYI.