M923A2 Air Brake Pressure Issues

[thesledge]

Well, We made it back home with my M923A2 after overcoming some brake issues with a temporary fix. Here is what happened and what we have done and where things are currently at.
We picked up the truck and everything was working perfectly. After driving about 50 miles, we started losing air pressure in both primary and secondary. So, we pulled over and started troubleshooting. We ended up replacing the air governor and still could not build pressure. So, in an effort to just get home, we hooked up an air compressor and generator in the bed of the truck and then connected the compressor line directly to the air dryer. We set the pressure to 80 and were able to keep about 70psi in the primary and secondary lines. This allowed the brakes to work all the way home (300 miles). Interesting side note is that about 50 miles from home, the pressure in the primary and secondary lines went up to about 110 and it seemed like something started working again....??? Anyways, after getting home and getting some rest, I did some more troubleshooting and now I need some further help. Here is where things currently stand and what I have found out at this point. I disconnected the primary line right out of the compressor that goes back towards the air dryer. This line has air coming out of it. I can hold my hand over it and stop the pressure. How much pressure should be coming out of the compressor and how do I measure this? If I hook this back up and check the pressure right before it goes in the dryer, it appears to be about the same amount of pressure. So, do I have a bad compressor? Is my governor not doing its job? Do I need to adjust my governor? Thoughts?? Thanks ahead of time for any help!

 

[MtnSnow]

Sounds like your compressor is not compressing which can be either a incorrectly adjusted governor or a faulty compressor itself.

 

[gimpyrobb]

Pull the air dryer and rebuild it, then adjust the air gov.

 

[thesledge]

Thanks for the replies. Question: How do I correctly adjust the governor?

 

[doghead]

Have you inspected your air dryer yet?

Did you confirm that the drain was not leaking?

You need to service your air dryer first.

Your new governor should have come preset.

 

[thesledge]

Thanks doghead! I will service the air dryer tomorrow.

 

[5tonman1971]

Sounds like your compressor is shot. If you can hold air back with your hand that's not a good thing.

 

[quickfarms]

A bad governor can cause this problem, it can also be caused by the purge valve on the air drier being stuck open.

 

[Artisan]

I installed an air filling Schrader valve w/ a 1/2" brass tee at the rearmost PRV*
on the DS, under the bed up high so I can pump up my air system
w/o the engine running, thus eliminating engine noise so I could listen
for leaks. I would suggest everyone do this PRIOR to any air
leak issues. You just pump it up and listen and or start squirting
all air line connections soapy water to look for leaks.

In this pic you are looking up at the DS just in front of the front rear axle.

I simply pulled things apart and cut in a 1/2" NPT brass tee and reconnected all.
I can pressurize backwards as far as it will go and forwards as well at the same time.


* I believe it is a PRV = Pressure Relief Valve ( don't quote me and someplease correct me if wrong.)

 

[doghead]

If the unloader valve in the compressor is stuck open, you may experience exactly what you have so far. This may be close to what would be needed to fix that issue. http://www.brettstruck.com.au/p/855...number-3018543x-3018543-3018527x-3018527.html

Have you tried following the troubleshooting section of the -24TM, where it covers air pressure issues?

 

[thesledge]

Thanks doghead! This seems like it might be the issue! I appreciate your time! I am going to work on this a bit more this week and will report back with what I find out. Hopefully, it will be good news that I fixed the issue and finally removed the generator and air compressor from the bed of the truck.

 

[thesledge]

Well, I finally got my new compressor in the mail today and got it swapped out. After getting everything back together and refilling the coolant and power steering, she fired right up and started building pressure. After adjusting the governor a little bit, she is maintaining 120psi. So, all is well. Thanks for the help along the way guys!

 

[MtnSnow]

Glad your getting compressed air again!