Why do the brake master cylinders run from either 82-83,82-88, 0r 90-92. (the latter of which is hard to find) My situation is that I swapped an 83 posi rear end with disc brakes making it 4 wheel disc. brakes were fine till recently. never changed the proportioning valve. i decided it was time to swap in the correct one. Plus the BMC needs replaced due to a leak. Does anyone think it would be a problem if I put a BMC for an 83 on there? I need to know if there would be a problem because I'm having brake issues and I wanna find out how to fix it before my car ends up plastered to the back of another one.

 

you should use the master cylinder for the 4 wheel disc. the piston is smaller. they are inexpensive from autozone.

 

GM says the master doesn't have to be changed:

https://www.thirdgen.org/forums/susp...fferences.html

82-83 cars are SAE. 84-88 are metric. IIRC, the thread pitch changed sometime in 89+.

For best brake performance, I'd certainly change the proportioning valve (valves were designed to optimize specific systems: drum or disc).

JamesC