Transmission difficult to shift Low-Neutral-High unless I pump the brake and release air to vent-stack

[Drryan]

Hello from NC! I have to shift my transmission a lot when using the crane and rear winch on my M936 wrecker. In order to use the crane, I need to shift it into Neutral on the floorboard and then back to High to drive it. My problem is that it wont shift from Neutral to High, or vice-versa unless I let the truck air-up to above 60PSI, then pump the brake to let some air out of the vent-stack, then it will shift easily. It's a PITA and should work regardless of the air pressure, I would think. Any ideas what I need to fix? Thank you!

 

[simp5782]

Hello from NC! I have to shift my transmission a lot when using the crane and rear winch on my M936 wrecker. In order to use the crane, I need to shift it into Neutral on the floorboard and then back to High to drive it. My problem is that it wont shift from Neutral to High, or vice-versa unless I let the truck air-up to above 60PSI, then pump the brake to let some air out of the vent-stack, then it will shift easily. It's a PITA and should work regardless of the air pressure, I would think. Any ideas what I need to fix? Thank you!

The interlock solenoid on the transfer case I'd stuck.

You can bypass it