Possible locked proportioning valve?

[broncoP]

Trying to finish my disc brake conversion. My latest and hopefully last hurdle is no fluid coming out to front brakes, haven't tried back yet. I put in a used disc prop valve. If its locked/closed, how do you open it? When I had the drums on it took awhile to get fluid out but it finally came out . I ended up using vacuum bleeder which was great.

 

[cldonley]

I've only had the problem once, and I replaced the prop valve with new. Not sure how you can dislodge a stuck valve; I would try a pressure pot. You can pressurize a bleeder pot to back bleed brakes from the discs up. Maybe putting pressure on from the disc side toward the valve will move it the other direction and open it up. You'd probably need to disconnect the supply line from the master to the prop valve to give the pressure a place to go. Good luck!

 

[clarrance]

I've had this problem with a brand new porportioning valves. If you google porportioning valve imbalance there is a lot of reading that talks about this problem. Some say to kick your brake pedal very quick and hard to release the stuck valve. I have also found the brake light switch to be a problem. The newer switches are not a smooth action and the pin on the bottom of the switch gets hung up on the piston and doesn't allow the piston to move freely. Since I don't use the brake light switch I just eliminated the switch and installed a flared plug in the brake light switch port. This allows the piston to move freely with no interference. Here is a crude drawing showing how the piston moves back and forth to compensate for the difference in brake line pressure when applying the brakes. You can see how the pin on the brake light switch can stop the piston from completely moving in one direction if the switch is sticky or gets hung up.

 

[cldonley]

This ^^^ looks like a good option. Drawing looks good to me!