Parking brake issue

[Joel Weiss]

Despite having replaced both the air actuator for the parking brake and the inside On/Off valve (the big yellow button), I am still having parking brake problems if the coach has been parked for more than a couple of days.  Here's what I've been able to observe:

1.  The chassis airs up quite well, each of the replacement items noted above has improved this and reduced air usage during driving.
2.  Releasing the parking brake for the first time in the day causes a noticeable decrease in pressure (10-20 pounds or more) and is often accompanied by a hissing sound coming from somewhere in the vicinity of the driver's seat.
3.  Quite often the air loss after release of the brake is more than the engine's compressor can overcome and the pressure will continue to decrease even with the engine running at high idle or above.
4.  However, re-applying the parking brake resolves the problem and the system quickly repressurizes. When the brake is applied, the hissing sound inside the coach stops.
5.  After sitting for 5-10 minutes and flicking the brake on and off the problem has so-far always resolved itself.  Once it does we don't have any further problems for the remainder of the day no matter how many times we re-apply the brake and turn the engine off.  I have no idea if the problem would self-resolve if I did nothing but I've always "played" with the brake while waiting.

Yesterday when we arrived at our winter site I used the manual valves and completely drained the air system.  I noticed what might have been some water vapor coming from two of the valves.   I haven't yet tried the system since I drained and repressurized it.

Unless draining the system has miraculously resolved this problem I'm probably going to have to have a technician come to our site so he can participate in starting the engine up and observing this issue.  The air dryer was last serviced 3 years ago.

Anyone have any ideas?

Joel

[Lee Welbanks]

Sounds like your parking brake relay valve is hanging up.

[Joel Weiss]

Where would it be located?  In the "console" next to the driver's seat where the main parking brake switch/valve is located?

[Edward Buker]

Joel,

When you have the brake on the air is released from the brake chamber and springs force the brake to actuate. When you release the brake air is passed on to the brake chamber to over come the spring so there is a fair amount of air needed to release the brake. If you lose air and that does not stop in the release position then the valve has to be faulty if you can hear air at the console. A leaking diaphragm at the brake actuator would not change characteristics as you reactuate it.   The fact that repeated movement changes what happens regarding air flow would seem to me points to the valve being at fault as Lee said.

Later Ed

[Joel Weiss]

Ed:

The valve that you push/pull to apply the brake was replaced last month; I was pretty sure that there was a problem with it.  But there continues to be a problem.  Lee Wellbanks has suggested the Parking Brake Relay Valve.  I didn't even know what that was, but now that I Googled it, it seems like a pretty good candidate.  Now all I need to find out is where it is located.  I can't localize the hiss well enough to do that.

Joel

[Edward Buker]

Joel,

I thought the valve in the console did the job, did not know about another component being the relay valve. I knew you replaced the button valve but thought you might have gotten a defective one. BCS would probably know where that relay valve is.

Later Ed

[Lee Welbanks]

Joel,

I thought the valve in the console did the job, did not know about another component being the relay valve. I knew you replaced the button valve but thought you might have gotten a defective one. BCS would probably know where that relay valve is.

Later Ed

The push pull valve in the console actuates the parking brake relay valve, if the relay hangs up it will continue to exhaust air. Here is a link to how a air system is done on a truck, pretty much the same as a air system on one of our coaches. It explains how all the system works.
http://www.thecartech.com/subjects/brakes/Air_Brake_Service_Systems.htm

[Joel Weiss]

The push pull valve in the console actuates the parking brake relay valve, if the relay hangs up it will continue to exhaust air. Here is a link to how a air system is done on a truck, pretty much the same as a air system on one of our coaches. It explains how all the system works.
http://www.thecartech.com/subjects/brakes/Air_Brake_Service_Systems.htm

Thanks; I now understand the system a bit better.  From what I've been told the relay valve is probably on the frame somewhere near the parking brake actuator.  Now I just need to find someone competent to replace it.  Most likely its a Meritor WABCO product and we'll also need to get a part number so one can be ordered.  At least I have several months this winter to resolve the problem.