Secondary side air leak

[EO2NMCB]

Truck is a M927 non abs. I can hear air leaking from the air intake. When I depress the treadle valve the leak goes away. I've checked break cans, Q2 Valve, valve under the step on driver side, no leaks into the vent lines and PPV valve, service rear glad hand had no leak. What am I missing? Tried downloading P2P could not get it to work. Only Secondary side is leaking, Primary side is fine.

 

[EO2NMCB]

I found my problem, I started at the vent lines from the air intake. Turned out to be a relay valve on the front drive axle.

 

[simp5782]

Truck is a M927 non abs. I can hear air leaking from the air intake. When I depress the treadle valve the leak goes away. I've checked break cans, Q2 Valve, valve under the step on driver side, no leaks into the vent lines and PPV valve, service rear glad hand had no leak. What am I missing? Tried downloading P2P could not get it to work. Only Secondary side is leaking, Primary side is fine.

You answered your own question. Treadle vakge. It vents to the intake to release pressure. Lowest hose for the treadle valve in the firewall is the vent. Remove it and see if you have air there with the pedal not depressed

Your relay valve for the front tandem axle you mean?

 

[EO2NMCB]

Yes the front tandem axel, I pulled both 1" vent lines and worked backwards.

 

[simp5782]

Yes the front tandem axel, I pulled both 1" vent lines and worked backwards.

Since you don't have abs it is a common R8 valve. Found cheap on ebay