I've got something strange going on with my air. When coming to a stop or braking relatively hard, I'm losing air pressure at an alarming rate. Stopped and asked a guy to depress the brake pedal while I listened to all six of the brake chambers and no leaks there. Maybe the air governor that sits on the drier? I put a new one on last year. I don't want to just throw parts at it but since those things are pretty inexpensive, maybe I just go ahead and change it?
Losing pressure bobtail as well.
Losing air pressure when braking hard or coming to a stop.
Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by spindrift, Oct 27, 2021.
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Im Going to guess the tractor brakes werent released when you had him push the brakes, or he barely touched the pedal.
Chock wheels
Build air
Release tractor brakes
Turn truck off
Wedge the pedal to 40-60 psi (really pushing the pedal)
Take your walkaround again
Im still betting its a brake chamber or hose
2nd option, the leak is the hose/tractor release valve itself and air loss is masking that air loss is happening there
3rd option is the brake pedal valve/hose itself, but you should have heard that when you were at the drivers side steerLoneRanger, Rideandrepair, Dino soar and 2 others Thank this. -
I checked again and confirmed it's not #1 or #3. I don't hear any air loss while it's occurring so I'm not sure how I would identify the issue if it was #2.
Rideandrepair Thanks this. -
If the air governor cuts in and you build the air until it kicks off your Governor is working correctly.
Just a thought but if you have something else that's leaking on the truck when you hit your brakes it will look more dramatic. Have you tried just shutting the truck down and seeing if you're losing air without hitting the brakes?
Some trucks the blend doors and other things are air actuated and you could have a leak somewhere else maybe.
Also I would build to full pressure and release the brakes and jam the paddle down with something and listen at the treadle valve and all the brake relay valves to see if you have any leak there (chock wheels).
If all else fails get the ultrasonic leak detector. I've been meaning to get one and now that I'm writing this I think I'll order it right away.Rideandrepair Thanks this. -
You say "ALARMING RATE"
What *exactly* does that mean?
We can rule out a brake chamber simply because its not getting progressively worse with time. Pancake failure usually progresses pretty fast.
As dino mentions, the brake relays or hoses under truck back to where they split is probably next on the agenda if you can get rule out the brake valve assembly itselfRideandrepair Thanks this. -
Rideandrepair Thanks this.
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And you can hear nothing anywhere while braking or when stopped?
No air hiss?
If thats the case, its shop time id wagerDino soar and Rideandrepair Thank this. -
How old are you OP? Maybe you’re just hard of hearing?
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LoneRanger and Rideandrepair Thank this.
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If it’s at home now, maybe ask the Little Lady to hold the brakes, or chalk the tires, put a 2x4 between the seat and pedal, parking brakes released, shut it off. Listen close, spray it with the water hose. I suspect the foot pedal or one of the relay valves.
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