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No Parking Brakes 1997 M1078

autolocators

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If the brakes work with the treadle (foot pedal) and the spring brakes fully engage when all the air is drained out, then somehow you have air feeding back into the spring brake release system. Or air lines are switched somewhere. Did you replace the check valve behind the front grill?
Negative on check valve replacement. Everything has been tricky on this truck. It was never put into service with the military. It has 60 miles on odo original packing slip was on windshield. We finally chased down the electrical gremlins but I'm thinking someone must have messed with something somewhere down the line. You may be on to something about airlines switched.

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Suprman

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If you take the front gladhand covers off does any air continuously leak from either? What about when brakes are applied? I would believe unicorns replaced your speedometer long before I believe your truck only has 60 miles in 20 years.
 

autolocators

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Suprman I understand your skepticism on mileage. Who knows. I tried checking both front gladhands with park brake and hitting brakes no air released from gladhands only from vent behind front bumper. Shows good air pressure above 120 for both

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doghead

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Were located in overtaxed sunny Commifornia. I just looked at our profile and it said location as Redlands?

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That's just wonderful, please change your profile to show that(as the rules request).
 

Suprman

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Air should release from the blue gladhand when you let off the brakes. Not much. A quick puff. If air cannot escape then you could have an issue where your brakes won't release. Maybe something is disconnected leading to that gladhand. First place I would look is under the front bumper at that check valve. Somehow air is getting fed into the spring brake release system. It's a good place to start. The red front gladhand line can be followed to the check valve.
 

NDT

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Still waiting to hear if the truck rolls with all air drained so at least we can eliminate stuck wedges on the rear axle as a cause.
 

NDT

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NDT when you say all air drained you mean both front and rear brakes? Truck will roll anytime unless wheels are chalked or physically pressing the brake pedal.

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Yes, please open all three drain cocks on the air tank reservoirs and tell us if the truck will still roll. Air pressure is needed to release the brake shoes on the rear axle which is the only axle used for the parking brake. If the shoes are released without air available, the mechanical mechanism that retracts them, the "wedges", are stuck in the actuated position.
 

Oxyacetylene

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You mentioned that there are air lines going up the the frame that aren't connected to anything. Those are vent lines; they are intentionally open. That doesn't fix your issue, but at least you know why those are open.
 

autolocators

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Unlock this emergency front glad hand this has to be unlocked for the parking brakes to work correctly.

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I have unblocked both front and rear gladhands red and blue. Still no **** parking brakes. I'm going to mess with it tomorrow and try draining all the air out of the system to see if that does anything.

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I have unblocked both front and rear gladhands red and blue. Still no **** parking brakes. I'm going to mess with it tomorrow and try draining all the air out of the system to see if that does anything.

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You should hear a loud sudden release of air when you set the parking brakes with the valve. Do you not hear this?

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Suprman

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I have had a bad anti compounding valve affect brake operation but only treadle function appeared to be affected. Somehow air is inadvertently being fed into the spring brake release circuit for towing. Maybe there is a way to temp disconnect this air circuit.
 

coachgeo

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IMHO at this point.... since these work like standard brakes on big rigs and with compatable parts... IMHO if you can stop while driving..... go visit your local Big Rig service guys. Often they are reasonably near a truck stop off of the interstate.
 

autolocators

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IMHO at this point.... since these work like standard brakes on big rigs and with compatable parts... IMHO if you can stop while driving..... go visit your local Big Rig service guys. Often they are reasonably near a truck stop off of the interstate.
This was my thoughts exactly I've had the truck already at a big rig shop and they have no clue. I'm almost thinking to drive it back to our normal auto repair shop where I work to let my guys try and figure it out since the big rig guys don't seem to know what the heck they are doing. I still have to try draining all the air to see if that releases the wedges like SUPRMAN suggested earlier.

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coachgeo

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This was my thoughts exactly I've had the truck already at a big rig shop and they have no clue. I'm almost thinking to drive it back to our normal auto repair shop where I work to let my guys try and figure it out since the big rig guys don't seem to know what the heck they are doing. I still have to try draining all the air to see if that releases the wedges like SUPRMAN suggested earlier. Sent from my SM-G928P using Tapatalk
Consider another big rig shop. Sounds like a that shop was tire changers?? From all have read in here.... these are standard airbrakes like any larger commercial truck such as a IH, Schoolbus, Kodiak etc.. Call around to see who works on those in your area? Brakes on such rigs are just enough different from auto's that average auto shop guys will be a bit befuddled. just my .02 definately drain the tanks though and see if that makes the park brake kick on. Wouldn't hurt to go to youtube and watch the videos there on wedge truck air brakes so you understand the concepts better too.
 
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