Mystery Air Leak behind cab of M35A3

[Mark3395]

Have been researching the manuals but haven't yet found info regarding a couple of small plastic lines coming downward from the back of the cab. One is venting huge amounts of air and the loss prevents the brakes from working. Have verified that the air tanks are fine.

Am continuing to search the manuals but surely could use a bit of info here.

Thanks much.

 

[HDN]

Have you been able to trace the vent lines? I can't remember which ones come up to the back of the cab.

Do you build any air at all or is it just going out the line?

 

[M35fan]

My A2 was leaking air from the vent line. Enough so that it wouldn't build pressure above 60 psi. I'm not very familiar with the A3s, but in my case it meant time to rebuild the air pack. The seals inside had hardened and vented too much. I believe the A3s have two air packs. Be worth tracing the leaking line back to its source. Good luck!

 

[Mark3395]

Thanks for the note. I've dug into the manuals and found diagrams of the brake system. Find no troubleshooting logic yet or anything telling how the system works. Still looking.

Amazing that the little tube completely vents all the air pressure to the brake system. It's only about 1/4 inch diameter but blows like crazy. Haven't had time to follow it but the diagrams from the manual will guide us. Problem is that I need to drop the truck down a slight slope using handbrakes to get the truck out of the way for now.

And the leak allows no pressure buildup at all in the brake system,

 

[gimpyrobb]

Only thing I can think of would be the air dryer.

 

[HDN]

Only thing I can think of would be the air dryer.

The air dryer vents out the bottom of the chassis at the air dryer outlet. It makes me wonder how it works for deep water fording, though!

 

[gimpyrobb]

Correct.
The location he mentioned could only be a rotted air tank or the air dryer.

He said he hasn't investigated yet.