I've got an 88 TA that came with a 10 bolt drum brake rear, and I am swapping in a 9 bolt from an 87 GTA. It has the crummy DM rear brakes, but they'll have to do until I can get the Baer setup. My question is, do I need to change the master cylinder/booster as well, or can I Use the old one. I tried the right master for a DM rear disc system, but I couldn't get any fluid out of the rear circuit, and I attributed this to the fact that the boosters are different. This is why I want to know if I can just use my old master, because I really don't want to swap boosters. Help!

 

i'd suspect the MC would work for either

 

Master cylinders, while different, are interchangeable between disc and drum rears. GM had a TSB on this for customers who wanted to change their pedal feel.