Do i need a different master cylinder to change to rear disc brakes? I got the pro valve for disc brake set up and have been told thats all i need. I have also heard that i need the master cylinder off of a disc brake set up?? I have an 85 rs with 10.5 disc brakes in the front and i just but a 9 bolt with disc brakes and will be installing that in my car

 

You will need the stock J-50 disc/drum master cyl.

 

could i already have a j 50 master cylinder is that the iron one? Will i need to replace the diaphram as well?

 

Lets go back to the beginning. What year is the car?

 

its a 1985 RS with 10.5 front disc brakes and im waiting for my rearend which is in the mail and i believe it has the steal calipers so i think that makes that a 88 or 89 im not positive on that though

 

Supposedly the 82-88 rear disc brakes (single piston iron calipers) require a special master cylinder. Frankly, I've had those brakes with both the "special" master and the normal one and have never noticed the difference. In fact, a friend of mine is running my old rear with the stock 92 drum MC and PV and the brakes seem to work about as well as they ever do.