Posted by John in La on December 01, 2015 at 05:08:42 from (96.33.136.54):
In Reply to: Help with semi brakes. posted by notjustair on November 30, 2015 at 22:40:45:
At first it sounded like you were describing a bad BP-R1 Bobtail Proportioning Relay Valve. This valve reduces air flow to the rear tractor brakes when there is no trailer to provide better control.
Then as I read on I realized you just have bad brakes Here is my reasoning.
1) With a trailer hooked the trailer is doing all the stopping; you just did not realize it until you used a trailer with electric brakes.
2) When you were bobtailing the Bobtail Proportioning Relay Valve was reducing the air flow to the truck brakes. Your truck brakes are so weak you found that releasing the trailer brakes; that took out the Bobtail Proportioning Relay Valve; so it provided full air pressure to the truck brakes. This extra air pressure gave you better stopping power.
3) your parking brakes do not work. You can take all the air out of the system and the parking brakes should still hold. They are held by spring pressure. If the springs are not holding the brakes tight you better fix that first.
Now is the problem you do not have them adjusted correctly or your shoes/drums are wore down so much they will not hold I can not answer. I do not think it could be a broken spring in the brake chamber or a wrong replacement brake chamber used as that would only effect 1 wheel. It sounds like you are haves equal problems with all wheels. If the brakes are adjusted correctly and you have the right amount of throw on the chamber rod I would be looking for glazed shoes or wore down drums.
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