M923 air brake work arounds....

[srodocker]

oh tony...

 

[M35A2-AZ]

I feel your pain, this is what GL did to my truck just moving it on there yard before I picked it up.

 

[wsucougarx]

Wow Tony. Your trucks seems to keep looking better and better every time I see her. Glad you got your truck to join the ranks of your others. You're going to have a tough decision to make for the July/August Rally

 

[Ord22]

i watched shipping wars sometime, its funny. congrads on your new addition!

 

[aggopian]

Good story truck looks great!

BTW your M813 looks awesome!!

 

[Csm Davis]

Okay I know I am late but maybe it will help someone when they have the same problems, if you would have read the tm's you would have found that there are two valves on the airtank in between the frame that you can shutoff one at a time to get pressure to the brakes. Sorry I didn't see your post sooner.

 

[quarkz]

CSM Davis,
Thank you for the info.
Maybe your suggestion and all the other air brake info in this thread will help the next un-lucky soul.

It wouldn't have done me much good as I wasn't able to jump start the M923 and get the engine running..

I will have to check that valve out this weekend.
Plus I need to repair the rear emergency connection/leak.

I did charge the batteries over the week.
One of the four needs 'special attention' as it put the digital battery charge into a CHECK Battery/Connections Mode.
So I disconnected those two batteries and ran it off of only two of the 6TLs.
Fired right up on the first try.
I don't hear that distinctive NHC250 rhythm I hear with my M813A1. It runs a lot smoother.
Getting happier with the truck all the time.

Now if the winds would drop below 20MPH I could get out the and work on her some more and get here out on the road where she belongs.

 

[Bolkbich]

Funny all my 250's sound different. Some have more power than others. My latest M923 sounds like a popcorn machine and has as much power, even after a tune-up.

 

[Andydieselpower]

Small world- the driver that delivered your M923 picked up one of our customers trucks going to WA this past Summer. Looks like he has tricked out his truck a little more with the road train style front bumper. That old T600 was kind of tired looking.

 

[nf6x]

Okay I know I am late but maybe it will help someone when they have the same problems, if you would have read the tm's you would have found that there are two valves on the airtank in between the frame that you can shutoff one at a time to get pressure to the brakes. Sorry I didn't see your post sooner.

I gave the -10 TM a first reading the other night, because I just won my first M923 in the GL auction on Thursday. I didn't see those valves mentioned, though I'll admit that I hardly skimmed the PMCS sections because I figure that they'll make a lot more sense once I have the truck in front of me, and I go through them line by line while I give my new truck its first thorough inspection. Do you recall where in the TMs those valves are discussed?

 

[quarkz]

I started to work on the air system today.
First I heated up the brass elbow on the rear emergency glad hand, removed it and reconfigured it so the valve would close the rear emergency line.

Made sure all the glad hand valves were closed, along with the four tank drain valves on the passenger side.
Started the truck and the pressure did not build on the dash gauges.
So I pulled out TM-2320-272-24-1 pg 2-197 Compressed Air Supply Troubleshooting.

Loosening the governor signal line verified the compressor was working.
Crawling under the truck I made sure the valves on the tanks were open.
In doing so I heard a hissing with a murmur that sounded like the compressor.
It came from the expello valve, as laid out in one of the flow diagrams.

It is positioned to expel moisture from the wet tank, but didn't seem to close all the way.
Could this cause pressure to not build? Can the expello be rebuilt? I didn't find any info on the expello's operation or repair. In the light tomorrow I will try to find a part number an look it up on the expello site.

The trouble shooting continues. I must get a pressure gauge tee to start working my way thru the air system.

 

[det rebel]

yes that could cause a big lose in pressure best way i have found to find air leaks is to tee in a air your tanks up to 70 or so to give you a little time then get you a spray bottle full of soap and water and spray down every connection and tubing while listening for air leaks works best while not running truck but some times has to be done

had a truck one time that when it got over 2000 rpm the torque pinched off the output from the compressor and caused it to leak but under 2000 and not running it would close off

 

[Csm Davis]

Tm 9-2320-272-10

Tm 9-2320-272-10 page 3-55 paragraph 3-12 you can shut the primary or secondary system down to get pressure back to the brakes

 

[Bolkbich]

Check the check valves (especially the one right after the dryer before the first air tank). When they get rusty and stuck , the dryer does just what your describing.

 

[nf6x]

Tm 9-2320-272-10 page 3-55 paragraph 3-12 you can shut the primary or secondary system down to get pressure back to the brakes

Got it! I haven't studied the maintenance section yet. Thank you!

 

[quarkz]

nf6x,
go to the TM's section for the 5 tons.
There is an application there that that has the 939's electrical and pneumatic system.
You can click thru it to follow the schematic, then you can click to get more info on a component, like how it operates or what it looks like. ( M939 P2P ) bottom of the page....
Just awesome software.

 

[OSO]

Good to see more trucks at your compound! I like that 80+ft slave cable . Too bad those slave cable adaptors didn't work out Great looking trucks!

 

[quarkz]

Thanx OSO.

Got to work on the air system a little more.
I hooked up the shop's air compressor thru a glad hand to the rear emergency glad hand (REGH) on the M923.

Both primary and secondary air guages quickly got up to 120 psi and the brake pedal became hard and the parking brake button on the dash felt hard when I pulled it out. I closed the rear emergency glad hand valve and disconnected the shop air.

I listened around and the Expello valve didn't leak anymore. I wasn't able to hear any other leaks either. I did not get out the soapy water though.

Next I started the truck and the dash light went out, lowered the hand brake and that dash light went out and the truck made and exhaust hiss. I put the truck in gear, started moving and tested the brakes. Stopped quit well.

Now I understand/have a feeling the delay that is commonly mentioned between pushing the pedal and when you feel the brakes grab.

But with the engine running the gages did not return to the 120 psi. With the M923 in park I cycle the brakes many times until both tanks were empty. So I turned off the engine and recharged the air system through the REGH.

And crawled under the truck to listen for leaks and check that all the tank valves were open, which they were. I did notice that the caging bolts on the 4 rear axles seemed to be backed out ~3". But I am guessing that when I operated the brakes it compressed the spring enough to release the caging bolts?

My first check today is to examine the compressor again. see what air I get coming out of the pump into the wet tank. Then I am going to check out Bolkbich's check valve for clogging/operation.

Attached is a *.jpg that I made from two of the previously mention P2P troubleshooting software.

 

[Stonepicker1]

Most of our problems with the M900's not building up air pressure was either the check valves bad on the air tanks(rusted on the inside,keeping them open) or the brake pedal(inside the pedal are o-rings that get junk and dirt in them so it lets air pass by)

If you hold the brake pedal to the foor and run the engine at a med rpm, it might just build up pressure. If you let off the brakes and the pressure goes back to 0, then your brake pedal needs cleaning or replaced. You will hear air leaking out the top of your intake stack with the truck off.

 

[quarkz]

OK,
Poor truck sat around for 3 months while I put in irrigation, planted seed and bought another Austin Champ. But being the show season I was really itching to get her operational.

So last night I crawled underneath and decided I would trace the air thru the system. Using the diagram above the first stop is the air dryer.

So I got out the big wrenches and loosened the in and out hoses to the air dryer.

Started the truck and climbed back under. The input hose was hissing, so I hooked it back up,

Then the I heard a his from the output fitting and the pressure relief valve,

I was getting ready to dis-assemble the relief valve on the air dryer but it wouldn't come off easily. So I put a finger over the outlet fitting and one over the pressure relief vent and the pressure started to build. When I felt a bit of pressure on my fingers, I quickly removed them from blocking the air. A quick puff and some debris came out of the outlet fitting.

So I did it again and again until no more debris came out. Then I covered the outlet fitting and listened to the pressure relief vent, it no longer leaked. Rust or CR@P must have been keeping the relief from resealing. So I hooked back up the outlet hose and after a few minutes of quiet I got a quick burst of air then quiet again. Things seemed to be working.

I climbed back up in the cab and the low air buzzer and light we still active and there was no pressure on the primary tank. I heard a hiss from the dash, it was the air to the wipers, so I replace the hose clamps and the hiss went away after tightening, but no primary pressure.

So after 20 minutes of hunting around, I remembered that in the debug portion of my adventure I was opening and closing valves underneath the truck. So I climbed bask under and sure enough I had the valve to the primary closed off.

Upon opening I heard a rush of air filling the tank and by the time I crawled back into the cab the low air light was off.

So this morning I scanned copies of all the GL documents for the SF-97 and made a trip to DOL and got her titles and tagged, (regular not historic) for $262.50.

I called a couple Insurance companies. New and with my current, Hagerty and $77 for 6 months or $158 for a year are the best I can do with $15K comprehensive. I think the cheap rate comes when it is just liability. I will have to ask for quotes on the minimum needed in WA.

But this isn't about Insurance it is about air system trouble shooting.

SO there is the close out to my adventure. I hope it help the next 939 owner that falls victim to air system woes.