<strong>07. </strong>PBS supplied a new master cylinder, and we got one matched to our truck’s four disc brakes. It originally had front discs and rear drums, and didn’t see a big improvement when we converted over to rear disc some years ago because we were still using a master cylinder meant for rear drum brakes. Disc brakes take more fluid volume than drums do. To properly supply a rear disc brake conversion, you need to swap in a master cylinder meant for disc brakes.