Air Question

[JTKenworth]

On my 1989 kenworth C500B, when ideling the air pressure will stay at 120, but when pulling a hill the pressure will max out the guage 150psi. I noticed the air dryer wasn't going off and not knowing when, if it was ever changed, I put a remaned on. It didn't fix anything, the pressure still climbs and the air dryer doesn't go off. Before I go tearing something apart I was wondering if anything like this has happend to anyone else?

 

[DirtHauler]

This sounds similar to what was happening to RobVG here is what worked for him
quote is from the original thread https://www.heavyequipmentforums.com/showthread.php?t=19990&highlight=dryer

Well, we parked it since we have 2 spare trucks. I'll get to it later.

Funny thing happend Tuesday. Driver called and said there was something wrong with his truck and he was coming in. When he pulled in, his truck sounded like a toy machine gun. The pop off valve on the compressor was going off rapid fire. Must have been overpresuring but it goes off at 150 and the gauges said 130.

Replaced it and...same thing. Checked the line from the Govenor to the Unloader it was fine. Replaced govenor... no luck, same thing. Pulled the unloader out and found it was gummed up. Also the top 'o' ring was toast. Put in a new unloader and it works like a champ.

To be honest, I had to call Kenworth and pick their brains. But now I've got more knowledge to fix the other truck when I can get to it.

ALSO here is a great page that shows how these parts all work.
http://www.zafr.com/trucktcom/brakes_pressure_components.htm

From looking at things, if your air dryer is not going off, i would say the govener looks like the issue. Since the unloader and the air dryer are both controlled by the govener. The unloader not turning on is causing the over preasurization, but it is controled by the govener. If it was just the unloader that was bad i think you would still have the govener activating the air dryer when you reach the set pressure.

 

[muzy]

Yes I would agree about the govener. muzy

 

[JTKenworth]

Thanks for the advice, I'm new to all this and don't know much about it at all. I'll replace the govener itself, At this point adjusting it won't help, right?

 

[DirtHauler]

Thanks for the advice, I'm new to all this and don't know much about it at all. I'll replace the govener itself, At this point adjusting it won't help, right?

They are inexpensive and usually they work or they don't. It is preset and should never need adjusting. You might be able to wack it with a hammer and get it to start working again, but that is really a last resort, get you back to the shop so you can fix it thing. They have alot of guts inside them.

 

[Muffler Bearing]

First off if your gauge says 150psi and no pressure reliefs are kicking out, I would guess that your gauge is off, I know most people don't have a spare gauge lying around to test with, But maybe you can thread in a schreader valve somewhere ( the gov may have one on it, #10 on diagram)and check the actual psi with a tire gauge or something. Also the Gov does need a signal from the air tank telling it what system psi is, Check that line and make sure it's clear. Once you locate this signal line, you could unthread it and blow shop air into the fitting on the governor with your truck running and the compressor should shut off. If this works your unloader if operating just fine. Also, since you are inspecting your air system, take a 1" wrench and pull off the steel braided line coming off the compressor head, only a quick 10sec blast of air should come out on this line, if air keeps coming you have a bad check valve.

As far as gov adjustments go, using Dirt hauler's handy diagram, if you remove#2 loosen #4 and turn #9 you can adjust the cut-in pressure on the governor, say change it from the preset 90psi to 100psi but the spring controls cut out and is not adjustable.
Good Luck!

 

[RobVG]

Great link DirtHauler- thanks!