Adjustable Proportional Valve - Do I need one?

"That 1 1/32 bore master has me concerned a little though. Most people that convert to 4 wheel discs use the 15/16 bore master. The 1 1/32 might give you a rock hard pedal and poor braking."

Doctor Diff sells a 15/16 bore master. His masters have the extra recess in the back of the piston to lock the pushrod in place. If you get one from a parts store, the back of the piston won't be machined to lock the pushrod.