[racerswift]

Had a brake dragging issue, after a long stop it seemed to be ok.  Temps went down.  Now at my location as soon as I release the parking brake there is a pretty massive brake system leak in the rear.  I'm pretty sure it is on that same passenger drive wheel.  As soon as I apply the parking brake the leak stops.

Any ideas what has failed.


I'm at Mountain Falls, North Carolina  Might also need mobile repair if it's not something I can do my self.  Any one have any recommendations for this area.

[arcticdude]

It's either the brake can or the air hose to the can. You'll have to get far enough under the rear to see which it is. The hose is easier than the can, by a little. If it was a small leak, you may have been dragging the brake for a while. I'd want to replace the shoes/pads on that wheel and really inspect the drum/rotor for heat related issues. It may be worth changing the wheel seal as well, for the same reason.

[Richard]

First, it takes air to release the park brake. Without air, a massive spring applies the brakes on the drive wheels.

So, the air that should be releasing the park brake when the button is pushed in is either leaking out of a hose or the diaphragm in the brake chamber.

Same thing as Arcticdude said, just with the explanation of why it is happening.

Do not drive until resolved.

[racerswift]

Thanks for the info. I have a couple questions. Is this common for a failed Brake Chamber to leak only when releasing the parking brake? It's holding air when the parking brake is applied and only leaks down when I release the brake.

There is a bolt on the end of the chamber, is this the caging bolt. I do not see one attached to the outside of the chamber like most of the videos show. Is this an integrated caging bolt?

[ian1959]

Hi there is no air going to the chamber when the park brake is on, inside the chamber there is a very large spring, this applies the brakes until the air is sent to it IE when you press the handbrake button OFF. Hand brake ON no air leak.
The big bolt is there so you, or your tow truck can manually release the brake by unscrewing this bolt to release the brake, you can in an emergency release the park brake with that bolt on that  brake but only if you blank off the leaking hose or else the other brake will bind too if your air will not build up.

[hexspeed]

Thanks for the info. I have a couple questions. Is this common for a failed Brake Chamber to leak only when releasing the parking brake? It's holding air when the parking brake is applied and only leaks down when I release the brake.

Ian's response is spot on. To get a better understanding of air brake functionality, the Canadian drivers' license and vehicle registration guys have some pretty thorough air brake manuals that have a lot of diagrams and good descriptions. Here's the page on parking brakes: https://www.sgi.sk.ca/air-brake/-/knowle...ake-system

BTW, don't uncage the parking brake until you're 100% sure you have another way of stopping the bus/keeping it from rolling away.

[racerswift]

Thanks for all the info.  

He indicated the canister failed on one side and was partially applying the brake for sometime.  He believes I will need to replace the pads and disk again (was just recently replaced).  Guess new brake canisters all around would be a good item to add to your list of replacements if it's been 20 years...