I've got a few shipping container chassis at work that have had a problem since we got them in our fleet in 2001, the air brakes for some reason every now and then lock up and will not release when out shunt drivers hook up, At first I thought the air was locked in the chamber and not allowing the brakes to release.. After draining both air tanks to purge the system of air they still will not release. It seems the only thing that will get them to release is when we pull them apart.
I have no idea what is causing them to do this, I am almost ready to replace the system on all of the units that do this..

Any ideas?

 

I would say bad relay valve anything else would be confined to one wheel only.

 

When they are locked up, remove the smaller line from the chamber to the quick release valve. If the air exhausts and the brakes release, you need a new quick release valve. Thats just one thing thats fairly quick and easy to find and fix. There could be a relay valve issues as well and there could be somethinkg wrong at the wheel end! Good luck.

 

could also be way out of adjustment and on the verge of "camming over" causing them to stay locked after air is applied, but I'm sure you've already ruled that out.

 

Are they s cam's or wedge brakes?
Possible high cam?
Important.. CHOCK ALL OF THE WHEELS FIRST
Can you hit the clevis on the slack adjuster and release them?

 

Are you getting air to the chambers with the brakes released???? How long has this thing sat.....the foundation part of the system may need taken apart, cleaned and lubed.....ie sticky bushings, rollers, pins all the good stuff.

 

these chassis move 27/7, they came from the factory with this defect.

 

What is the date of manufacturer, and are these chassis equiped with abs?

 

They are all 2001 - 2002 and they all have ABS.. WABCO systems

 

Any codes???

 

Also its not uncommon to be incorrectly plumbed from the factory

 

Hook a tractor to the chassis and put your air lines on it, then release the trailer brakes only. Go to the red glad hand and pull it off the trailer while it is charged, listen for the air releasing from the trailer glad hand. If you have a slow release of air and/or the trailer brakes have a delayed engagement then suspect a faulty or contaminated quick release valve. You should have a rapid violent evacuation of air from the trailer glad hand along with immediate brake engagement. The only other items that will cause the problems that you are having are a tractor protection valve, or a brake foundation issue,(shoe's,bushings,hardware,etc), if it only happens when outside drivers hook to the chassis, then it could be a tractor protection valve issue, but if it happens with your equipment also the I would lean toward the trailer quick release valve being the culprit. I have seen problems like this when drivers go to drop a trailer and they use the trolley brake to hold the trailer so they can push the tractor against the king pin to release the 5th wheel, then set the parking brake with the trolley still charging the service brake, this added pressure some time stays locked in the quick release valve if it is contaminated, however it usually will gradually release after sitting for a little while.

Hope this helps, Tim