Pete 389. Parking brake won't release, please help

A box of trailer door bolts, landing gear bolts, more bolts big and small. The more you can get in there the better you will manage small stuff that might ######ig a truck to moving again without a service call or tow until shop. Its all relative.

It also increases your understanding of that truck of yours.

 

The service and park sides of the brake system are seperated by a seal on the park chamber's pushrod. When that seal blows, park system air will leak through into the service side of the chamber and out the nearest valve's exhaust. In your case its likely the valve that was replaced.

When the park chamber diaphragm blows, air will puke out of the failed chamber itself whenever the park brakes are released.

When the service chamber diaphragm blows, air will leak from the vent holes in the service portion of the chamber any time you apply the service brakes.

 

SPSAUERLAND Is steering you correctly. A little additional info though. If the push rod seal between the service and spring chamber starts leaking and you release your park brake the air enters the spring brake side, leaks into the service brake side and exits through the service brake line and flows backwards toward the service relay valve where it is vented to the atmosphere. Changing the service relay valve as you can likely see is pointless. Sometimes you can hear the air flowing through the chamber, sometimes you can’t. If you had a stethoscope, you probably could. If you disconnect service line from chamber and release the park brake and air flows out of the service side inlet, that tells the tale. You could pinch the service lines one at a time and release the park brake and see if air is still exiting through the relay valve. When it isn’t, that’s the bad chamber.

 

That's interesting. QR1 is just a quick release valve. Having a hard time seeing how that would cause air to leak out the exhaust valve of the relay? Unless it was the QR1 that was leaking the whole time and the first mechanic thought it was the relay?

 

Good to hear you found someone else... I'm guessing he probably looked at you crazy when you told him the other mechanic wanted to replace the push pull in the cab.

 

They run a QR-1C on Peterbilt for parking brake control and anti-compounding. Air could be leaking out of balance port back feeding to the service brake relay valve. I have had this once also, but always check brake chambers first because usually the culprit. Capping balance port on QR-1C would have told you if that is issue and would be able to drive to a repair facility with it capped.

 

Interesting. The joys of not being there in person to see the whole story lol.