Red button will not push in

smblain

New Member
I have a 90 freightliner I use for hauling grain on the farm. Hooked up to trailer yesterday and the red button will not push in. Truck brakes worked fine until I hooked to trailer. The yellow button will not push in either.

Unhook gladhands and yellow button works and the red will blow air but still difficult to push in.

Tried a different trailer with the same results.

I replaced the tractor protection valve in the cab a few years ago trying to fix a problem (which it didn't) so I do not believe it to be the problem but maybe? I just remember it not being much fun...

I have unhooked and blew air through many line but nothing has helped so far

Any ideas?

Thank you
 
Is there a blockage in the red line on the trailer?
With no trailer hooked up can you push in the red knob and get good airflow out of the red gladhand?
 
Hmmm, well. The valve in the dash itself could be bad. A bad brake can can back feed through a relay valve and cause it too, sometimes. This is something where I’m throwing darts at the wall without having my hands on it.
 
Is the problem that the knobs won't move inward, or is it that they do press inward but they pop right back out?
 
They move in but wont stay in and are very difficult to push in as there is pressure pushing against.
 
You don't have the red and blue lines crossed?

Yeah I know it's a dumb question but we gotta start somewhere.
 
Drain all the air tanks on the truck with the truck off. If the knobs are still hard to push in there something mechanically wrong in the the valve itself
 

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