The air pressure will only build up past 70 when the truck starts rolling down the street. Changed check valve last time and pressure built up. So changed it again and this time problem still there. The minute I started driving yesterday pressure built to 110. Could anyone give me an idea on what is happening?. Thanks CRASH
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Air breaks on Mack dump truck
- Thread starter Crash
- Start date
Wes J
Senior Member
Could be an intermittent issue with the compressor or compressor cutout. This time of year, I always suspect ice.
Wes J
Senior Member
It's been a while, but I'm thinking changing that unit on a Mack requires a little more flexibility than it does on that Cat 
mitch504
Senior Member
It could also be the unloader valves in the head not closing all the way until hot, an air leak on the compressor discharge hose.
As far as Governors being hard to get to on Macks, most of them are on top of the compressor, and easy to reach, many of them are remote mounted, and very easy to get to, and then, there are the ones up under the cab. If it's my truck, I just leave them there, and mount the new one somewhere else.
As far as Governors being hard to get to on Macks, most of them are on top of the compressor, and easy to reach, many of them are remote mounted, and very easy to get to, and then, there are the ones up under the cab. If it's my truck, I just leave them there, and mount the new one somewhere else.
It's a 2001 Mack, I saw the compressor on right side of motor low , I didn't get a chance to work on it today, he had me working on a J D 670 excavator .. Thanks for responding I will look tomorrow, anything you can tell me helps, my diesel work was mainly on boats. First air breaks I've tried to diagnose. Thank you for your help!!! Crash
Does it build air when you run at high idle or does it actually have to be driving? If the compressor output hose is leaking it can be very hard to hear with motor running and check valve keeps the tank from draining back that way if you suspect that have someone else shut the truck off so you can listen
kshansen
Senior Member
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- Mar 11, 2012
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Or if possible disconnect the discharge line from air compressor and adapt to a fitting to supply shop air to it. That way you don't have to have engine running, makes it lots easier to hear a leak. Also it does not take too big a leak to cause that type of a problem. And if you are an old guy like me it helps to find the youngest guy or gal you can find to listen for the leak. Spent a lot of time trying to find one on a Cat off-highway truck and this young guy comes along and says: "It's right here!"
Truck Shop
Senior Member
Being a 2001 it should have an air dryer from factory, possibly the purge has a constant leak. Or reservoir to governor plugged. But I would lean
toward the D-2 governor or unloader valves sticking in the compressor. Some compressors the intake can be removed and you can manually trip
the unloaders with a screwdriver. That's heavy on the some.
Truck Shop
toward the D-2 governor or unloader valves sticking in the compressor. Some compressors the intake can be removed and you can manually trip
the unloaders with a screwdriver. That's heavy on the some.
Truck Shop