I have a 1998 379 pete with a 3406e cat. Replaced air filter in dryer and govoner and replaced the foot pedal brake valve. The air pressure won't build up properly. It will stay at a pressure, goes up to 120 when you hit the brake it will drop down to 80lbs or so, sometimes it stay like that sometimes is goes down further. Then takes awhile to build back up. I appreciate all help. Thanks
1998 379 air not building up
Discussion in 'Peterbilt Forum' started by cindymz, Nov 3, 2013.
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KW Cajun Thanks this.
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you must find the air leak, air it up to 120psi {chock wheels} em. brakes off, have foot brake pushed full down, get out find leak with motor off.
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It sounds like an air governor or air dryer problem. However, I would check the pressure release valves on your air tanks. You may want to get someone to listen while you work the brakes to see if they can hear the leak. When you changed out the air governor, did you make sure you plugged the right holes? Air dryers can also get grit in the valve that won't allow the air to build properly. It could be any number of things that are leaking. With that much of a leak it should not be too difficult to find. You may also want to check the pressure release valve, sometimes called a pop off valve on the air compressor. Good luck.
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I'm betting bad pancake in a brake chamber on one of the back axles.
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what about the unloader in the top of compressor? a new kit cost about 15.00 & easy to put in. my first guess would be the blue air line going to trailer. along with the red line. since you already changed governor, if you find no leaks. unloader kit would be my next guess.
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Sounds like a big leak in the brake circuit.
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Thanks guys, I'll do that and let you know what happens.
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I did replace the govoner again and builds up now. Now when I push the valves in the the red arrow on the gauge drops to about 90 psi. You can hear air out of the valves with your foot on the brake. Does it sound like a brake chamber on the trailer?
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