M1088 air leak from trailer brake valve in cab

[PowerstrokeNC]

So my 1088 leaks air out of the trailer brake valve lever in the cab when you depress the brake pedal. At first I thought it was the trailer valve itself, so I sourced another one and put it in.
Well it leaks just the same as before, anybody had this happen to them?

thanks

 

[tennmogger]

You might have a treadle valve (foot brake) leaking when depressed. The rush of air out of the vent up front (center line behind grill) has to source through the trailer or truck brake valve on the dash so sounds like it's leaking in the dash. Been there done that. Had dirt in the treadle valve. Easy to verify: Have someone stand in front of the truck and listen for the vent passing air.

There is a write-up here:

http://www.steelsoldiers.com/showthread.php?140345-Air-Brake-Info-and-Troubleshooting

 

[PowerstrokeNC]

Pretty sure air is coming coming out of trailer valve since it blows on my hand when I cap the trailer valve.... I will double check though.

 

[Suprman]

Does it look like the original trailer valve had been recently replaced?

 

[PowerstrokeNC]

I replaced the original with the one I bought from you actually and the result was the same, but I need to double check that I am not getting fooled by the under dash exhaust valve....

 

[Suprman]

I have seen several trucks come thru the auctions with what appear to be newly replaced parts, especially dash valves, that lines are switched by accident. Either by the military or GP trying to put stuff back together for a more saleable truck.

 

[PowerstrokeNC]

Funny you say that as I started to wonder if the valve was getting some form of back pressure. Mmmmm

 

[Suprman]

Service brake air feeding back.

 

[jcarter0909]

So my 1088 leaks air out of the trailer brake valve lever in the cab when you depress the brake pedal. At first I thought it was the trailer valve itself, so I sourced another one and put it in.
Well it leaks just the same as before, anybody had this happen to them?

thanks

@PowerstrokeNC; Did you ever figure out what the issue was here? I seem to have the same problem with my 1088.