Park valve venting out exhaust

[dhirocz]

Rebuilt my mv3 valve this weekend, since I haven't given it any love since I had the truck and recently I started noticing it leaking out the exhaust port with the truck in park with the foot pedal allied only.

Valve works fine. Except it still leaks. Doesn't leak with the tractor brakes released.

From what I can find, some troubleshooting matrixes mention that either the two way valve or the quick release valve can backfeed into the park valve and cause this issue. Some also mention a bad foot brake valve.

I'm still waiting for my service manual to arrive. Until then I don't have any air system diagrams specifically for this truck to help pinpoint the source of the problem, so any advice would be helpful. I'd rather not throw parts at it, even though at their age I might replace them all as a function of preventative maintenance.

The park valve works fine otherwise.