Brake Question M923A2

[DDM923A2]

1991 M923A2 brakes are bleeding off to rear gladhand which is closed and the buildup of pressure applies the brakes after driving a couple of miles. When I open the gladhand the pressure is releaved and the brakes unlock. If I leave the gladhand open the truck dumps its air when I press the brake so that's no good.
Background Information: When I bought the truck I thought the brakes worked but in reality they were dragging. I hired a mechanic to work on the truck in my driveway. All was going well until he didn't show up after doing some brake work. Last I heard he was in the hospital. He thought he had repaired the problem but it is not repaired and I have no way of knowing what all he did. Other than brakes the truck runs like a top because he did all maintanance needed and seemed to do an excellent job.
Question: How do I get the brakes to vent to the front gladhand like it is supposed to do? The front gladhand has no on/off valve and has a vent made to handle the release of air.
Could the mechanic have simply switched 2 of the air lines by mistake? My brain does not comprehend technical manuals as I am a hands on show me and I can do it learner.
Location: I am located in Rock Hill, SC (near Charlotte, NC) and would be happy to pay someone to get the brakes working. Anyone close?

 

[simp5782]

Insure the front passengers service valve is not restricted. the valve is always open. it has no valve. Pretty sure you have a bad treadle valve. Aka brake pedal valve

Checking this is by chock the wheels. Truck running. Parking brake off. Start removing the air lines off the treadle valve on the engine bay side. Remove the lines starting at the bottom. And see if you have air with the brake pedal not depressed. The top 2 air lines are supply lines. Do not remove those.

You can also leave the rear air service open and pull up on the pedal and see if it stops. Brake pedal is the place to start. Check and report back before we go chasing valves.

 

[DDM923A2]

Insure the front passengers service valve is not restricted. the valve is always open. it has no valve. Pretty sure you have a bad treadle valve. Aka brake pedal valve

Checking this is by chock the wheels. Truck running. Parking brake off. Start removing the air lines off the treadle valve on the engine bay side. Remove the lines starting at the bottom. And see if you have air with the brake pedal not depressed. The top 2 air lines are supply lines. Do not remove those.

The service valve is checked and working with no restriction.

Interesting you point to the treadle valve because the mechanic removed the entire assembly, took it to his shop, and rebuilt it. Something obviously went wrong either on the rebuild or the reinstall.

Thank you for the advice simp5782

 

[simp5782]

The service valve is checked and working with no restriction.

Interesting you point to the treadle valve because the mechanic removed the entire assembly, took it to his shop, and rebuilt it. Something obviously went wrong either on the rebuild or the reinstall.

Thank you for the advice simp5782

Buy a replacement valve. the rebuild kits do cause issues most of the time. Ive tried to do it myself a few times to no avail part numbers are. 286775 and 102352 or any E7 valve type. Tge lower pedal part swaps over

 

[DDM923A2]

Buy a replacement valve. the rebuild kits do cause issues most of the time. Ive tried to do it myself a few times to no avail part numbers are. 286775 and 102352 or any E7 valve type. Tge lower pedal part swaps over

Good information... Thank you