Modified Proportioning Valve for Rear Disc Brakes

by Troy Morris - 0riginally on www.bogoffroad.com

Coming out of the master cylinder are two sets of lines, one for the front brakes and one for the rear brakes. From there the lines feed into the 'combination valve' The 'combination valve' does a couple of things. One half feeds the front brakes. So there are two lines leaving it for the left and right caliper. The other half, which is the proportioning valve, feeds the rear brake drums or in this case, discs. The combination valve is the on the right side of the master cylinder.

The proportioning valve part of the 'combination valve' unit is actually on the front of the device so it's the closet to the grill. Drums use wheel cylinders. Wheel cylinders use much less brake fluid to work. Your front brakes do 70 - 80% of all the braking for your vehicle. The proportioning valve controls how much fluid is allowed to go to the rear brakes. When you swap in disc brakes in the rear of a system that had drums you must compensate for the extra fluid requirement that a caliper piston needs vs. the amount of fluid a wheel cylinder needs. On most systems all you have to do is modify the proportioning valve to allow more fluid to go the rear calipers. This is easily done.

All you have to do is use a pair of pliers to hold the combination valve body so you don't bend any lines. Then use the appropriate sized socket for and remove the vent nut on the front of the proportioning valve. The vent nut has a rubber nipple on it so you can't miss it. Unscrew the vent nut; pull out the spring and the plunger. On the end of the plunger will be a rubber o-ring. Remove the o-ring. Re-install the plunger, spring, and vent nut. Bleed the front and rear brakes and your done. This will make a big difference in the fluid going to the rear.

When I first added my Currie with the ford explorer discs I was really disappointed. In fact the braking felt worse. I called Currie and this is what they instructed me to do. I now have 8,000 miles since the conversion and I can lock the rear 33's if I had to.