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How do I go about recentering the piston in the brake proportioning valve? I have next to no front brake action, as the pedal goes half way to the floor and then the rears engage. I had a brake failure and did all 4 calipers with O ring rebuild kits. After bleeding the brakes and putting 3+ quarts of fluid through the system, I read some info on the prop. valve. I unscrewed the warning switch from the side of the prop. valve and see that the valve(plunger) inside is not centered as it should be and not allowing hydraulics to the front as it should be doing. Can anyone explain the procedure for recentering? TIA
Duane
Just three quarts of DOT3 so far? You are well on your way to an avg 55-gallon drum.
The piston can be centered by a few quick jabs of the pedal. But only if all the bleeders are closed and no new leaks in the system.
In the future, if you want the piston to stay centered, you will need a specail little tool to hold it into position.
Click on my profile, then albums, brake bleeding for info.
What year is your car? It makes a huge difference. Take a picture of the valve. Sometimes people install the wrong valve. The earlier cars DON'T have a normal proportioning valve. It is only designed to light the brake light and shouldn't be stuck to one side or the other. If it is stuck,,,, it's a bad valve.
If you have a 74, it should be the new style, pressure difference shutoff, valve. It is only designed to shut off pressure to the failed side.
Forgot to mention my car is a '72 with manual brakes. Original proportioning valve as I've had the car for just 48 years. I've tried jabbing the brake pedal, as suggested, with no results, and I mean I literally put everything into it many times. A GM tech with over 40 years told me to crack one of the fittings at the prop. valve and have an assistant give a slow push halfway on the pedal, and close it before he lets the pedal return. I'm going to try this tomorrow, and see if the valve moves. Got my fingers crossed. If that doesn't work, I'll try pressure bleeding through a bleeder to see if that works. Fingers crossed.
Duane
If your car has the original valve,,,, it isn't a proportioning, it is just a brake failure light switch. It isn't supposed to stay stuck to one side or the other. If it is, the switch is all gummed up. It should only light the brake warning light when you have a failure and pressure on the pedal. It does not shut off pressure to either side of the brakes when working properly. If you don't have front brakes, there is a different problem.
On my '68 I couldnt bleed the brakes, so I rebuilt the brake system.
Rookie me didnt know the brake warning bulb was burned out. It would have shown the system had a fault in it.
I finally removed and disassembled the brake valve...it was stuck/jammed so that only the rear brakes worked.
I disassembled the valve...cleaned the sludge out...honed the cylinder wall just enough to remove the thin layer of stain..the O-rings were in great shape...added a few drops of brake fluid to the O-rings and the bore...reassembled and centered the piston...installed a new warning bulb...tested the bulb by pushing the piston off-center each way to provide a ground for the warning bulb
The valve worked perfectly after the repair....re-bled the system with no problems
I wonder if you had flushed it with brake fluid, if that would have cleaned it out? You can use a small rod to push in one end to move the shuttle back and forth.
After looking at all the pictures and illustrations of prop valves, I believe mine is centered correctly. The brake light does not come on with the ignition on and pressure applied to the brake pedal. My wife helped with bleeding yesterday. She did the pedal work and I took care at the bleeders. We now have a pretty decent pedal with just a small amount of pedal travel, but more than I've ever had. If temps get a little cooler, we'll give the team bleeding one more shot. On the other hand, I've replaced everything, mast. cyl., calipers rebuilt, new pads, front brake hoses replaced with Russell S.S. but I haven't put the Russell SS hoses on the rear. If we get a decent pedal tomorrow, i'll do the rear hoses in a week or two. I know I should have done the hoses earlier, but they were in the bottom of the box and I forgot about them. I'll let everyone know how it goes. Thanks again. I couldn't have done this without all the help here.
Duane
What pads did you install. Many of the pads are high temp style that advertise how good they are. If you are racing your car these are great. I have tried them. For everyday driving I have found the cheap organic pad to be the best stopping power.
Brake proportioning valve question
