Disc Brake Rear Axle Swap into '79 GS
 

Hey all, I'm getting a disc brake rear end from a 81 model GSL and I have a few questions. Firstly, while the Mazspeed tut doesn't mention the proportioning valve, I've noticed that some people recommend getting it along with the axle. What exactly is the difference between the valve I have now and the valve from the GSL? What difficulties would I have if were to leave the original valve in place? Secondly, has anyone had any success finding an adaptor to make the hard lines on my '79 work with the lines for the rear calipers? I was hoping I wasn't going to have to replace all the hard lines. Could I just get a new fitting and flare the existing lines? Thirdly, the mounting points for the links didn't change between '79 and '81 did it? I know that the 84/85 models had lowered the mounting points for the trailing links, but I want to make sure I won't run into any suprises from the '81 axle. Finally, is the rear sway bar on the '81 thicker/better than the rear bar on my '79?

I'm getting a little tired of waiting for the inside wheel to catch after coming out a turn. ;) Hopefully the LSD can help me shave some time off my AutoX runs and catch up to that Miata. (Shakes Fist)

Thanks in advance for your advice.

I'm in the midst of doing the same thing to my '79, but with a 85 rear. I found a proportioning valve. switching it helps to keep the front/rear brake balance equal. It takes more or less pressure (cant remember which) for the drum brakes to engage. If you don't change it, your front brakes may lock up before your rear brakes. or vise versa. (again, cant remember which).

I believe JDuncan found some sort of adapters to switch the thread pitches. But I was just going to run over to AutoZone and either switch the fittings or replace the lines all together. they get a little crusty after 24 years. Another option if you don't already have SS brake lines would be to buy a set from mazdatrix, they sell a set that's made specifically for putting a FB rear on a SA.

hope that helps. I havnt put mine on yet, so im not sure about the whole linkage issue.

I did the swap on mine.... but luckily, I had a donor car to rob and pillage parts off of. You're gonna need a GSL Master cylinder, a GSL proportioning valve, and the SS brake lines are one of the best investments I've spent on the car.


It's VERY straightforward when it comes to putting the new rear end on... it goes like this... take bolts off of old one, drop rear end, put in new rear end, replace bolts. It doesn't get much simpler. Also, check your diff to see if it needs a rebuild... mine is starting to go...

Just curious, why would you need the master as well as the proportioning valve? Is the bore or stroke different on the disk brakes' master?