I had something weird happen today. Started the L9000 dump truck to haul some clay. Left it to build air pressure while I drove over to start the track loader. Came back and the truck only had about 90 PSI air pressure and a loud air leak. I had enough air to release the brakes so drove to the clay pile. I've had minor air leaks stop before but this was much worse. I left the truck running so I wouldn't have to wait for it to build air again. I hauled 2 loads and on the way back for a 3rd load the leak completely stopped. When I was checking it seemed like the leak was coming from the passenger side where I assume the heater core would be. Very strange. What could cause a leak like that and then stop 15 minutes or so later? Could overnight temps. just below freezing be a possible cause? It's never done it before in cool temps. though. I've also noticed my low air buzzer shuts off at about 65 PSI when it used to shut off around 60. Compressor seems good and cuts off at about 118 PSI. Brakes will dynamite so I think the air system is OK.
Does it have a dryer? Purge valve.
I believe it does but the sound could only be heard in the cab. I've heard the purge valve leaking but this was a more significant leak. Looking online, someone else had the valve for the trailer brakes do something similar and stop after 15 minutes. I thought maybe the cooler weather had something to do with it.
Yes--dash valves can leaking to exhaust port with colder weather.
Just went though this on a roll-off truck I take care of. Fixed several external leaks. Let it sit and it’s still leaking. Finally parked it outside where I could hear and it was bypassing in the dash valve.
That's good to know. When I first got the truck it had a slight hissing sound most times when I shut it off. That seemed to fix itself too. This last leak I thought a line blew or something and I'd have to take the dash apart. So glad it stopped. I'm wondering if the truck may have sat for awhile before I bought it. The hoist switch had a bad ground and didn't work half the time.
I've had dash valves that do this same thing, but it's usually the trailer valve since it's the one that bleeds down and sets itself after the truck has been shut off. If you had shut the truck off without setting the brakes, I'd say it's even more likely it was your dash valve.
That would lead to bad break cans.
I always put the brakes on when I park it. I've never needed to use the trailer brake circuit. Is there anything you can do when you get a dash valve leaking like this or just wait and hope it stops after everything warms up? Its never done this before.
It will go along seeping then get worse as time goes by. if that's what it is.
If it is a dash valve, is it located behind the dash or on the engine side of the firewall? Wondering how difficult it is to get at if I have to. The dash panel on the drivers side with all the gauges is already zip tied in place on the bottom.
In the dash, MV3 valve style it should be. Yellow & Red?
Yes yellow and red on the left side of the steering wheel but the leak was coming from the passenger side somewhere. I'm not going to worry about unless it happens again. Is it good to operate the red valve occasionally to clean it out?