Kenworth w900 breaks are not releasing

[arazdolgin]

Hi, can’t find any solution. Breaks not released and pushing in without me. Changed pedal break valve and dash air trailer/truck breaks. Still not released. Break pedal gauge shows pressure up. Should be zero. Do you think it might be electric problems? Or air valve somewhere? Any ideas? What it’s?

[Rawze]

if not a valve then maybe ...
possibly a parking brake chamber back-feeding into the service brake system?


{just the beer talkin'}...
maybe disconnect some brake line circuits at different points and attach the end of a baloon over the open ends to see what direction the air is bleeding in from?

[arazdolgin]

So what I found. Brakes on bobtail is working good (stopping/driving) with light breaks on huh. When I hooked to the trailer with red air hose, I can drive and breaks on truck/trailer released. When i attach blue air hose, breaks not releasing. I cannot drive with blue air hose. So some problems with blue air lines or some valve attached to it.

Changed brake pedal valve, dash hand break valve. Might be Tractor protection valve? Bought tonight and will try to install tomo morning.

Or might be relay valve? If somebody experienced this, please give food for thoughts how that Kenworth system works. Cheers

[hhow55]

http://www.suspensionspecialists.com/tec..._Chart.pdf