Red knob not popping out.

Most tractor protection valves are all one unit. Can't replace separate. Usually easy to do yourself, if inclined to do so.

 

Oh i might add. If you pull off service gladhand from trailer. The red button, knob whatever should pop out at around 60psi, when your air gets down to that point. Not pop out instantly.

 

You sure about that. I've pulled that line off multiple times over the years, on different tractors, and it flows air until 60.
I mean if it falls off when your going down the highway, the spring brakes are gonna come on instantly on the trailer.

I've had the service brake fall off with a loaded trailer, and it was a B to stop.

 

The red knob WILL NOT pop out instantly if you break the red gladhand. The trailer brakes need to apply instantly but the tractor air supply will need to drop down to around 60ish before it pops.

 

Think proper name is tractor protection valve. Yellow and red push knobs on dash. If you undo whatever holds them secure, and pull them out..they are one unit hooked to air lines. Proper way to check is with engine off, tractor brakes set (yellow knob pulled out). Leave red knob in and pull off service line to trailer (red marked gladhand). Air rushes out hop up and watch air psi. When psi gets to around 60psi it should pop out.

 

Correct

 

Blue is service, red is emergency or supply.

The two valves come together, so you replace them both. I just bought one to put on, but I have heard they are not easy to replace. The hoses that are attached are not that long, so you have to swing wrenches in the dashboard.