Air Brake Problem

[dlor1]

I have a 1989 Blue Bird TC 2000 with 235K miles. The air brakes have begun to act a little funny. Most of the time when I press the brakes the front left brake does not work until I break rather hard and it finally knocks fairly loudly and engages. I've adjusted the brakes with no inprovement. Any ideas.

 

[dlor1]

Thanks Macguyver. Well once I've applied enough brake pedal and I hear the clunk, I have full breaking power. Once in a while all breaks function normally but not too often. Also when it does clunk and it's wet out it locks up the tire, so I would suspect that there's pressure buildup just that the shoe isn't pressing up against the drum.

 

[the_experience03]

I would give that chamber a good inspection. It sounds to me like the pushrod may be tweaked. There are other symptoms that could cause what you are describing. Start by liberally greasing the S-cams (and the steering components while you're up there) and closely inspecting the brakes through their travel. I have found this to be easiest with a partner actuating the treadle as this allows me to watch what the chambers are doing and spot excess runout, etc.

 

[KC10Chief]

I'm not familiar with air brakes, but it sounds like you have a caliper hanging up. It happens on hydraulic brakes. I can't imagine that a caliper for your bus would be too terribly expensive.

 

[John Whelan]

I agree with the lube solution, the clunk can also be caused by a seized s-cam roller [If you have older Eaton air brakes they use a 2 piece roller assembly] but I would definitely remove the drum and take a closer look.
John

 

[dlor1]

greased all fittings and it has made it a little better but not proper. and I forgot to mentkon that sometimes when I use the brakes the pedal does not want to return all the way and the brakes drag slightly. Not a lot but drags bit, the pedal doesn't return all the way to the up position. I have to drive barefoot so I can pull the pedal back the last 1/8 in or so to disengage the brakes. any other idears?

 

[dlor1]

Anyone know how to diagnose this brake problem if I check the valve? Or any pointers?

 

[the_experience03]

Try putting an air pressure gauge on a "tee" fitting inline between the supply line and the brake chamber itself. If it is retaining pressure you likely have a problem with the dump valve on the chamber itself or your treadle valve is not closing all the way and is allowing a small amount or pressure to get to the brakes.

If you determine that there is in fact pressure there then disconnect the "tee" from the chambers and put a plug in the open end of it. If it registers pressure after sealing it up you will know that the problem lies with the treadle or something else further upstream and not with the chamber.