M939 Front Axle Switch Valve problem?

I am having a problem with a M939 truck and typing this message on behalf of our mechanic.


The problem is the truck is receiving air to both lines going to the front axle dash valve. It should only be getting supply on one line, but is getting it from both. Air is going through the weep hole.

We have tried putting in two new valves, but have had the same result.

Anybody else run into this problem?

Any help would be greatly appreciated.

Your linear valve on the transfer case where the shift lever is bad. The line that goes from the linear from the dash supplies air to it when the switch is flipped. However the linear valve has a bypass to engage the 6x6 when the transfer case shift lever is put into low range.

Easy fix Is to remove the linear valve and splice the air line on the frame rail and run it to the 6x6 actuator valve so when the switch is flipped it locks in.

Thanks for the quick responses. We did as instructed and seems to be working now. Thanks again.