72 Duster Resurrection

Before you go and buy a master cylinder, or remanned calipers i'm gonna give you some more info. This pertains to fluid dynamics. Some folks think bigger bore master cylinder equals a harder grabbing brake. Its actually opposite. It will result in a firmer pedal, but you will have to push harder for the same result at the wheels.

Now if you enlarge the pistons at the caliper end, the pedal gets softer because the fluid spreads out over a larger piston surface, however that surface has more area for the fluid to push against than a smaller caliper piston. So what you end up with is a softer pedal, but a firmer tighter grab at the wheels.

If your going to redo the front disc brakes, i am assuming you are going to buy remanned calipers, the ones for your A body brake setup use calipers with a 2.60" diameter piston. In rock auto you can buy M body calipers that will fit right on your A body disc brakes and use the same A body pads and A body brake lines. These use a 2.75" caliper piston. So your pedal will be softer, but will grip tighter at the wheels.

At this point you can still either use a stock pick manual disc/drum master cylinder or an M body master cylinder with plastic reservoir from rock auto on closeout new for $12.29. Look up 1984 diplomat. Bore size is 1&1/32" i believe a manual disc / drum master setup for an A body is the same piston dimensions but is cast iron and uber expensive, but i guess with the $38 adaptor needed to run the late model M body master it all works out to be about the same.