Rear Brakes Locking Up After Disc Install

[Gator Alum]

I installed the POL kit with front discs, power brake booster, and proportioning valve. I also installed a 2lb residual check valve for front and a 10 pound for the rear. The truck currently has 3/16" line throughout and a single line going to the front that T's off and a single line to the rear that T's off.

The rear brakes have a major tendency to lock up rather quickly under normal braking conditions. The pedal seems soft/light until the bottom and then the brakes grab hard and the rears lock up which tends to wake the neighbors.

Could it be improper drum adjustment in the rear? Maybe improper adjustment of the push rod on the MC?

As always, any help/insight is appreciated.

-Danny

[G&R's57GMC]

Start by bleeding the brakes again until you get a solid peddle.

Next use an adjustable proportioning valve instead of the one you have. Install it in the rear circuit after the 10# residual valve.

[mknittle]

Like G&R said,
I use adjustable proportioning valves because the factory ones have caused the same problems you have in some of my builds. Most factory ones aren't really proportioning valves, they are balance valves that even the pressure front to rear.

You could be right about the M.C push rod. I would rebleed the system first and go from there. I had a 68 4X4 that always needed to be bled a couple times every time I worked on the brakes.

[_Ogre]

bleeder screws on top?
drum brakes adjusted for slight drag?
not sure where your mc is located. i assume under floor since your using residual valves. confirm rod is correct
re-bleed until you have a firm pedal
if you end up needing an adjustable prop valve, i have one listed in the parts forum