Trailer Brakes not holding

Could be a couple of things. Could be the spring inside the brake chamber is broken so the parking brake does not fully engage. Could be the slack adjusters are worn out and not holding the correct brake adjustment. Could be the brake pads (linings) are worn out and not holding anymore. Could be the s cam bushings are worn out and puts the brake shoes crooked into the brake drums, so they don't hold effectively. Could be the air valves on the trailer are not pushing the air to the brake chambers. First of all, if you have to manually adjust the slack adjusters to tighten the brakes up to less than a 2 inch stroke, the slack adjusters are probably worn out and need replacing. They also need grease occasionaly as do the s-cam bushings. Also be careful around old brake chambers, the rings that bolt together and hold the chamber together will rust and sometimes give out, sending the top half of the brake chamber exploding and this can cause serious injury. Take it to a certified shop if you can. AND one more item is the tractor protection valve usually located on the rear of the cab. They wear out also, and are the valve that controls air going to the trailer.

 

Just to clarify, your trailer spring parking brakes work but when you apply the trailer brakes with the johnson bar they won't hold? If that's true I'd say your foundation brakes (drums/discs, pads, cams) are probably ok. I suspect you'd be looking at an air problem on the service side. When you hear the air moving, does it eventually stop or does the air sound like it keeps moving until you release the brakes?

 

Disc or drum brakes?

 

There's a couple possibilities it could be. If its only this trailer that does it then the issue is in the trailer. If you can replicate this problem on other trailers, your issue is in the truck. There are a number of different valves, like the tractor protection valve or the 2 way check valve that is plumbed in between your foot treadle and johnson bar, that could be the culprit.

 

Had the same issue about a month ago. It was ice in the line at the service brake control on trailer