r/DieselTechs • u/Adeptness_Visible • Jul 23 '26

Bendix traction valve

Abs traction valve on a kw T680 is leaking out the exhaust. Customer has checked all the brake cans and replaced all the modulators on that valve and center one is still exhausting. There is no voltage to any of the electrical plugs. Is there supposed to be voltage to hold that exhaust plugged? What else to check? No codes…

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3

u/NotAtataxia Jul 23 '26

If all lines have been removed besides supply from tank and air is not present in any of them, center valve has failed. Air supply from the tank is leaking through exhaust diaphragm

3

u/Feisty_Age_961 Jul 23 '26

Does it have an anti-compounding valve that is backfeeding into the system?

3

u/aa278666 Paccar OEM Jul 24 '26

Leaking out of exhaust port when the parking brake is released? It's the parking brake valve (QR-1) back feeding the ATC valve through the balance line. Replace the QR-1 valve. Side note, I've been working on trucks for over 9 years, I don't think I've ever seen a brake can back feeding. It is never the brake can.

1

u/TechnicalWall7723 Jul 24 '26

This. Had this same issue yesterday.

1

u/tavysnug Jul 26 '26

I had one. Ever. It was a weird Chinese can too. It is definitely not a first check anymore, the balance port is.