M1088 tractor air at spring brakes released with parking brake engaged

[jmb6741]

I always check those 2 way check valves under the cab behind the driver step if air is coming out of the front gladhands. I've had the brakes lock up if I close off that front glad hand also. Easiest way to check is take the valve apart on the truck and check the diaphragm for holes or cracks.

 

[Suprman]

Check valve behind bumper gunked open. 2 of the 3 check valves under the drivers area had gunk in them. Brakes work as intended. Learning experience. And the cause of all these issues is:

 

[NDT]

Now where would one find one of those?????