5th wheel issue

Tap the linkage with a hammer, right where the cylinder connects to the mechanism that pulls the pins...I had a T680 that did that. It would retract the pins just fine, but no matter how perfect the pins were lined up, it wouldn't move them into the locked position until you started it with a hammer. I lubed everything you could lube and it didn't help.

 

If you can reach it hooked up, I would stay connected

 

Is there any chance of ice being built up in the track and in the locking pins and levers?

Also you don't need air to lock them. You need air to release. They lock by cutting the air supply off just like spring brakes.

 

Sounds like the cylinder spring is broke. Or something is on the cylinder rod keeping it from moving. I don't think it would be an air leak at the firewall in this case. Lift the hood and engage the slide action...listen for rushing air on the d/s firewall by the engine. That's were the air lines are as they lead up to the dash switch.