m936A2 brakes slowly lock-up...what gives?

[halftrack]

Unfortunately my air brake knowledge is not as sharp as the pencil I use at work.

While finally being able to drive the M936A2 wrecker, after about 5 minutes of casual driving, the rear (and just the rear) brakes began to drag until they finally immobilize the entire truck from totally locking-up.

I checked the air tank gages and both primary and secondary are full of air (120psi). I end up shutting down the truck and drain the air and start back up again and everything is fine for about another 5 minutes and then you can start to feel them drag again. What gives?

Any mechanic out there familiar with the M939 brake system, your suggestions would be much appreciated. By the Way, the truck does have the ABS mod and new air dryer system on it.

 

[NDT]

Did you check the front glad hand cover for the vent hole????????????

 

[hot rod deuce]

Yeah man! +1 to that. Some wise a$$ put a valve on my M932A1.

If you use the over ride button on the dash does it stop? This just puts direct air to the release side of the chamber.

Try to put a gauge on one of the chambers.
Its either air or spring putting the rear brakes on.


Becasue its only the rear it sounds like spring to me.

You could:

Try putting a gauge on the apply press line of the brake chamber to see if some how air is leaking through the valve and putting them on

Or you are lossing release pressure, a gauge will tell you that too.

 

[halftrack]

Thanks hot rod. I was thinking the same thing because it is just the rears. Tomorrow will tell all. I keep ya'll posted.