Peterbilt ABS and dash valve leaking.

Please tell us what valve is leaking air and where exactly is the air leaking from?

This air leaks only when the yellow knob is in, but stops leaking when depressing the brake pedal.

Just want to be clear- When did it start? suddenly? after a repair?

 

I got an 05’ 379… having the same issues as you except when I depress brake pedal air spills out exhaust on dash valve. So far have replaced abs valve,tractor protection valve,and 1 brake chamber…. I’m kinda at a loss.. commenting to follow.

 

ABS valve is from vent on bottom? Dash valves leak air from where?

 

Really wondering if air is leaking from the dash valves or if you just hear air flow through them.
I would start with crimping off or disconnecting drive axle service hoses one at a time. That is while leaking looking for a bad chamber.

 

Abs spillage from bottom vent dash spillage from exhaust port

 

I am stumped. Would like to know what you find.
Is there another like a QR1 C ? connected in the system anywhere? I would look for something like that being bad. Maybe a two way check valve.