Parking Brakes Won't Release on '96 Pete 379

Yes. Slack adjusters effect brake tension when parked. If they are out of adjustment the shoes will not be tight enough against the drum and the truck could still roll.

sounds like you may have an issue with the shoes and drums surfaces having rust on them and sticking. It only takes a little humidity to make this happen. Release them with valve and Tap them with hammer to get them to back off. Pump fresh grease in them and re-adjust them. Work them off and on with the foot peddle a dozen or so times to get them to stay loose again. Then check to camshafts and bushings for wear play.

 

Not uncommon for all the 30/30’s to leak. Rare but not unusual. But they have to be a really bad leak to keep them from releasing. You would hear it in that case.

 

yes release parking brakes. hit the shoes with a hammer they should be loose and move left to right. if they dont move hit them left to right till they move.

 

Get an air pressure gauge and verify that you're getting at least 90 psi to the quick release valve when you push the yellow knob in. Its better to use a "T" inline with the gauge, but you can just connect the gauge directly to the end of the air line. Theres lots of places in the air system where airflow/pressure can be restricted by rust or debris. If there is a restriction, sometimes you can get lucky and use a blow gun to reverse pressure through the line to unclog it.

 

Are you positive you have the new valve installed correctly and that it's the correct one? I've also seen those valves be faulty right out of the box.

I installed a new proportioning valve and when I would bobtail I had to stab the brakes to get it to totally release once I was driving. That drag would be lessened once a trailer was hooked up but would still persist. I drove it like that for years because I thought it was normal when bobtailing.

Checked it with an infrared thermometer and realized it caused my drum to warp and in turn caused a vibration that I also chased for years. I never would have guessed it would all be related to that valve. Changed it out for a new one and problem solved.

 

I 2nd what was mentioned above. Never trust the dash gauge. I'd plumb in a test gauge and make sure you've got adequate pressure to the chambers. If a diaphragm is leaking, you'd hear it. If the seal between the park and service sides of a chamber is leaking, you'd here it exhausting constantly at the relay or a quick release in the service side.

I have also seen the chambers themselves pack up with fine sand and prevent the brakes from completely releasing. You should see some small drain holes in the park side of the chamber, give the chamber a light smack with your hand and see if anything comes out of the holes.