A sticking emergency brake

[jelmore]

This has only happened one time ...

First, a confession: I had not raised the rear end from being parked on a sloping site and I had raised the tag (I was very distracted). Maybe those things caused the emergency brake to not release but I don't think so. I tried it again a couple of days later and this did not happen.

I had released the brake, put the bus in drive and it wouldn't move. It lunged just a bit as if the brake was on. Back to neutral and cycled the brake on and off a few times. All air pressures appeared normal. Everything sounded normal. Tried reverse and it wouldn't move. Put the tag down, put the bus at ride height, the transmission back to drive again and it moved fine and then noticed nothing odd while driving or stopping.

Could this be a bent or corroded mechanical link or rod? We're 250 miles from a Prevost shop. Could this be trusted to a truck shop? I'm pretty sure I don't want to mess with brake chambers if that's the issue.

Anything I can check with a visual inspection? Thanks.

[Jon Wehrenberg]

Jim,

The emergency brake release is actually air being applied to a diaphragm in the emergency brake portion of the dual brake chambers on the tag and drive axle on your coach. If your push the brake release your gauges should indicate a small drop in air pressure and then stabilize. That is the indication the chamber is being pressurized and the emergency brake portion has been released.

On occasion our brakes will "lock", typically due to moisture and being parked for a while. In my case I can put it in drive and the bus will not go forward. I hold my foot on the brake and put it in reverse and usually that is all it takes to "unlock" the brakes. I don't know if it is the shoes sticking to the drum or if something else is at play, but that does the trick.

I assume you are dealing with a bus fully up to pressure, that you hear no rapid or loud escape of air when the brakes are released, and that when released you only have a few pounds pressure drop to indicate the chambers are pressurized to relase the brake.

If all else fails you can manually release the emergency brakes by using the "t" bolts supplied with each chamber and the nut holding the bolts to manually engage the bolt in the rear of the brake chamber, and using the tightening of the nut to retract the brake. That is not going to be necessary unless you have a failed diaphragm, in which case you will hear a lot of air.

Jon

[truk4u]

Mine will not usually move after driving in the rain and setting for 3 or 4 weeks just like Jon said. I have found that when that happens, I cycle the brake pedal a few times and it free's up. I had the same thing happen on the 97 Marathon, so I don't think it's unusual.

[jelmore]

Jon, my experience was the same as what you describe. No air leaks and good pressures. This hasn't happened before, so maybe it's age related. Thanks for the reply.

[Jon Wehrenberg]

It's not age related, but is a result as Tom said of high humidity or running in the rain, and sitting for a while with the parking brake on.

Usually just the slightest backward force such as putting it in reverse works for me. I don't actually have to move the bus backwards.