Join Date: Dec 2001
Location: Belleville, Illinois
Thanked 22 Times in 17 Posts
Re: 4whl disc brakes on YJ, need larger Master Cyl?
Usually disk brake master cylinders have a larger reservoir because brake fluid provides the wear adjustment. As the pads wear the caliper pistons move out farther and stay there. That requires more fluid to fill the caliper.
Disk brakes usually require a smaller piston in the master cylinder because they inherently take more pressure to activate, but don't need the large volume of fluid that drum brakes do just to move the shoes out to the drums.
But that is affected by the pedal linkage ratio, the piston area in the caliper, the proportioning valve, and the ratio of front to rear braking you need on your vehicle.
You need to do some research on your entire braking system and figure out what master cylinder you need. You might not help yourself just by the swapping master cylinder for one you think might work better.
A couple more observations; rear brakes don't do much of the braking anyway, so don't expect a big improvement in stopping performance.
Don't drive with those perches unwelded! If the axel slips you'll be in a heap o' trouble.