Airbrake problem

[Tom and Pat Fudale]

I am having a problem with air brake pressure. Riding down the road with engine RPM up the air pressure will be always be in the 110-130 range. But when with the engine RPM low while jockeying into a parking spot the air pressure will drop and the low pressure buzzer will sound. The air pressure will not rebuild unless I have it in fast idle and then it takes a much longer time to rebuild now.It just wont increase in low idle.

[Edward Buker]

Tom,

It could be that there is a leak in the air system that while at low RPM the loss exceeds the compressor output. It could also be that the compressor is not putting out the volume of air that it should. In either case the fault needs to be understood and corrected. It is a safety issue.

Later Ed

[Gerald Farris]

Tom,
It is normal for the air pressure to drop enough for the warning lite to come on if you are jockeying into a parking spot and applying the brakes often with the engine idling. It will also take a little while for the engine to rebuild the air pressure at an idle. However, if the air pressure will not rebuild, and you are sure that you are not just being impatient, you either have an air leak, or a defective air compressor. From my experience, the highest probability is that there if nothing wrong with the coach.

Gerald
  

[Edward Buker]

Tom,

I guess you need to judge regarding what you have experienced in the past vs your latest experience and if that represents a change in your coaches air system performance. Certainly as Gerald points out you could feather the brake pedal on and off enough to deplete more air than the compressor can supply at idle and that would be normal.

What sounded abnormal to me is when you indicated that the air would not build at idle, that does not seem normal by any means. This site gives you some leak down test routines and an air build timing test. The air build test is a function of tank size so it is not too meaningful without past data for comparision. Your best bet is to do this test and post your results and see if another owner of the same coach will do the same tests and help compare the results.

http://www.cdldigest.com/pre_trip_inspection/brake_check.html

Later Ed

[Tom and Pat Fudale]

Thanks for the input but I decided to take in to the truck shop since it could taken care by a pro since it a safety issue.

[Mandy Canales]

I had the same problem with our coach recently.  When stopping for lunch or at a rest stop for about 30 minutes or more the air pressure gauge would be down to about 40 pounds.  Then I had to wait for a few minutes until the air pressure built back up.  I finally took the coach to a truck repair place to check it out.  They found one of the four front air valves was allowing air to be released.  They checked all four valves and found them in good working order.  They recommended that I check those air valves regularly, at least once a week if not more.  When you expel some of the air from those valves its supposed to also expel the moisture that had built up in them.  Now the problem is solved.
Mandy

[Joel Ashley]

I hadn't thought of that possibility, and I'm glad Mandy mentioned it.  If your '05 is like our '06, the bleeder valves are mounted on a plate with the remote air hose connector next to the battery box behind the rearmost curbside access door.  It could be as simple as one of those bleeder valves having been bumped slightly out of position, debris jamming it, or as Mandy suggests, one has a bad seal.  The hose connector could have debris jamming it slightly open, or a bad seal, too.  It would be a simple thing to initially check before going to a service center.

Joel

[Paul Schwalen]

About a year ago I had a similar problem with the brakes.  I took it to Ring Power in Orlando and they found one of the rear brake chambers had failed.  They recommended I change both rear chambers and have not had a problem since.

Just another view.

Paul

[Tom and Pat Fudale]

Well as it always happens it turns out that the air compressor was the cause and after dropping a few bucks it is now problem solved

[Edward Buker]

Tom,

Glad you found the issue and your coach is behaving again. It may not be a bad idea to feather your brakes at an idle just until the compressor kicks in and then time the fill time for your air resovoir until the compressor kicks back off for your own records. May be handy in the long run to verify if things are as they were regarding air build up.

Later Ed