Can't get a hard brake pedal with engine running
I am at a loss on how to get brakes on this Jeep. I just replaced the proportioning valve because the old one was leaking. I STILL cannot get a good, steady pedal.
Here's the odd part - I can get a decent-height, hard pedal as long as the engine is off. However, when it's running and the brake booster is getting vacuum, the pedal goes straight to the floor with no effort whatsoever. I understand this is the booster working, but it seems to be boosting a little too much. I have bled and bled and bled and bled and bled. No air coming out.
Everything in this system has been replaced except for the front brake pads, the metal lines, and the booster. The rear brake have been adjusted to spec. This is the second master cylinder (this one is a new one that has been bench bled 3 times so far).
The new proportioning valve came from Inline Tube and was bled per their instructions - they say DO NOT touch the pin on this valve. Rather, bleed as normal. They said I still have air, but NO AIR IS COMING OUT. So I bled as normal and followed their troubleshooting instructions. The valve is still centered, but when bleeding the fronts, the pedal will only go to a point and stop. When bleeding the rear brakes, it will go all the way to the floor. Why??
Also, the booster has started making a hissing sound after the engine is turned off, leaking down the vacuum it had. It didn't used to do this... Is this related to my issue or is this a problem at all?
What can I do to get the same hard pedal I have when the engine is not running?
1984 CJ7 Laredo
4.0 I-6 / T5 / D300 / D30 / D44
Black Diamond 3" lift, 33" tires, 4.11 gears