I am having a weird problem with my gauges on my 1995 M1078 and any help would be really appreciated.
My front and rear air brake gauges read over 120psi all the time. When I start the truck, the gauges pin to the right and I never hear a warning buzzer that the tanks are getting up to pressure. After a few minutes, the dryer purges and I can release the parking brake and drive and stop normally. I can pump the brakes several times very quickly and the gauges don't change and the brakes don't lock up from lack of air pressure.
The troubleshooting manual said it could be the governor is not unloading and to check the air flow from the wet tank to the governor. I have verified:
-that there is air coming out of the governor to feed the dryer, checked at the governor
-there is air coming from the wet tank to the governor, checked at the governor
-there is air going from the dryer to the wet tank, checked at the wet tank
Air purges from the dryer purge valve every 1.5 minutes.
There is a valve that comes off the side of the wet tank and it is leaking from the seam. I took it apart and the rubber diaphragm looks serviceable. It seems to be installed correctly with the #1 on the wet tank side and the #2 on the far side.
The rear trailer protection valve leaks when I hit the brakes. I haven't had a chance to verify it yet, but I suspect it is a bad diaphragm, I am just mentioning it for completeness.
I have heard the warning buzzer, so I know the buzzer works. It just isn't sounding, I suspect because the gauges never say the pressure is below 120psi. When the buzzer sounds, the gauges still say over 120psi, so I am not sure why it is sounding.
I tried replacing the front brake gauge and it gave me the same symptoms.
The only other clue I have is that I did see the gauges read under 120psi once when I was backing down my driveway. i was riding the brake and as I mentioned, that vents air from the trailer protection valve. I tried stepping on the brake to recreate the effect, but it did not affect the gauges.
Any suggestions on what to try next would be appreciated.
My front and rear air brake gauges read over 120psi all the time. When I start the truck, the gauges pin to the right and I never hear a warning buzzer that the tanks are getting up to pressure. After a few minutes, the dryer purges and I can release the parking brake and drive and stop normally. I can pump the brakes several times very quickly and the gauges don't change and the brakes don't lock up from lack of air pressure.
The troubleshooting manual said it could be the governor is not unloading and to check the air flow from the wet tank to the governor. I have verified:
-that there is air coming out of the governor to feed the dryer, checked at the governor
-there is air coming from the wet tank to the governor, checked at the governor
-there is air going from the dryer to the wet tank, checked at the wet tank
Air purges from the dryer purge valve every 1.5 minutes.
There is a valve that comes off the side of the wet tank and it is leaking from the seam. I took it apart and the rubber diaphragm looks serviceable. It seems to be installed correctly with the #1 on the wet tank side and the #2 on the far side.
The rear trailer protection valve leaks when I hit the brakes. I haven't had a chance to verify it yet, but I suspect it is a bad diaphragm, I am just mentioning it for completeness.
I have heard the warning buzzer, so I know the buzzer works. It just isn't sounding, I suspect because the gauges never say the pressure is below 120psi. When the buzzer sounds, the gauges still say over 120psi, so I am not sure why it is sounding.
I tried replacing the front brake gauge and it gave me the same symptoms.
The only other clue I have is that I did see the gauges read under 120psi once when I was backing down my driveway. i was riding the brake and as I mentioned, that vents air from the trailer protection valve. I tried stepping on the brake to recreate the effect, but it did not affect the gauges.
Any suggestions on what to try next would be appreciated.
