1991 m931a2 lost air on recovery.

[tstates]

Ok I need to reach out to you all. I have searched for hours and have looked through the TM. I have not been able to find a specific answer. Last week I recovered a 931. It ran great and was an hour into trip when primary tank lost psi. it came back up a few times then went to zero. I knew i had real problems so before my secondary lost all psi I found a place to pull over. we were running from the big ice storm in N.E, so we had to leave my truck to be towed. I am leaning towards a blown head gasket or un-loader valve in compressor. could someone tell me a source for the head gasket and un-loader valve?? Does anyone have pics of the procedure?? My truck is 500 miles away. I plan to go work on it next week. Just thought some of the experts may be able to give me a jump start and some help. Thanks so much in advance.

 

[Scott88M]

I drive garbage trucks with air brakes for work in Rhode Island. Sometimes in this bitterly cold NE weather we will lose pressure like that when an air valve with a little water in it freezes the valve open. This happens usually while driving or when just hitting the brakes in general. I'm no expert but it's another possibility.

 

[doghead]

It is a a good chance that your issue is simply frozen moisture in the air system.

Unfortunately your air dryer is probably way past due to be serviced. I would go with a new desiccant filter for sure.

 

[Floridianson]

Did the wet tank have air checking a the bleeders just not the outher tanks? Look for the thread PPV. or search.

 

[Suprman]

In the cold the air dryer expello valve can get stuck open when it vents. If you climb under the truck and listen to see if air is coming out of there with the engine running you can usually stick your finger in the hole and push it back up to stop the leak. Sometimes a little wd40 sprayed in there can get it moving properly again but if thats the case it should be rebuilt.

 

[tstates]

Guys, thanks for the fast response. I do have an extra air dryer kit. I was going to bring it just in case. I do remember hearing air leaking out of the dryer. I dont remember it venting like my other truck, and spitting H2O out. When we started the truck it was over psi'ing due to PPV. once it warmed up, it began to hold normal psi. But as you said, everything may be full of H2O, and something froze up. I wanted to go back up next week with every trick in the book I could get. And hopefully get it fixed for the 500 mile trip. I wish I had more time to trouble shoot it when we had the problem. We just ran out of time. I did get the towing company to allow me to try to wrench on it, thats a start.

 

[camoyj7]

My air dryer froze open and will not build air. Think it's pretty common on these truck.

 

[tstates]

I sure hope that is what it is. Does anyone know a procedure for listening or feeling around the air compressor to see if it is leaking? I know the TM. calls for a procedure to feel the exit psi line for heat, and check for psi to Governor and what not. I went on line and found a haldex trouble shooting guide, but it was just general practice stuff for air brake systems. I also plan on bringing some gasket material just in case I may be able to make one. Just don't know where to order a kit?

 

[73m819]

If you do not have a alcohol injector for your air system, install one, this WILL take care of your air system freeze up problem and add the checking and filling to your walk around..

 

[BKubu]

I am not trying to pick on the OP, but this is a perfect reason why newly acquired trucks should not be driven out. Things fail when you don't know a truck. Heck, they fail when you do know a truck well. Better to get it home and go over it carefully. Sure, it costs more, but that money buys peace of mind and no headaches. Also, what happens when you get back after a 500 mile run and the diagnosis was wrong and it is some other problem, or you have a different problem? Good luck, my friend!

 

[Scarecrow1]

Ron where do you find info on buying and installing the alcohol kits ???

 

[73m819]

There is a kit in the back of the -10 along with the other add on kits, or instead of a military kit why not just put a standard civi kit which can be gotten from/ordered from any big truck parts house, or napa truck, the plus side for this is that it may be cheaper then the military one.
These kits are VERY simple, very few moving parts, it works just like a line oiler, about the only moving parts are the drain, the fill, and the flow control.

 

[juanprado]

The non abs trucks originally had an alcohol kit on the a0 & a1. I still have the bottle and bracket left on mine. When they were upgraded to ABS, the alcohol system was removed / disconnected.

The a2s started with abs OE.

I don't know the exact reason why but I don't believe you can have an air dryer and alcohol at the same time or why didn't uncle leave it on?

a properly working air dryer with heater should do the trick?

 

[BKubu]

The non abs trucks originally had an alcohol kit on the a0 & a1. I still have the bottle and bracket left on mine. When they were upgraded to ABS, the alcohol system was removed / disconnected.

The a2s started with abs OE.

I don't know the exact reason why but I don't believe you can have an air dryer and alcohol at the same time or why didn't uncle leave it on?

a properly working air dryer with heater should do the trick?

JUANPRADO, I am not sure that I've seen the bracket after they removed the alcohol kit. Can you attach a pic? Thanks!

 

[Floridianson]

From what I have read the alcohol system need to be down stream from the air dryer. Seems like the air dryer is needing to be serviced if your having problems. Google Haldex A72420 this is what would be need to install after the air dryer.http://www.haldex.com/en/North-Amer.../Air-DryerAir-Line/Alcohol-Evaporator-/A72420

 

[juanprado]

JUANPRADO, I am not sure that I've seen the bracket after they removed the alcohol kit. Can you attach a pic? Thanks!

Bruce,

See this thread for a picture I posted a while ago
http://www.steelsoldiers.com/showth...his-bottle-on-a-M923&highlight=alcohol+bottle

 

[2old2humps]

On the trip home from Ripley in my m931a2, i lost primary air. it turned out the filter on air dryer unscrewed. messed up the threads,had to bypass it to get home. the dryer had been replaced in 2012. they must not have tightened the filter.

 

[tstates]

Very interesting. I plan on heading back up on Tuesday to troubleshoot. I ordered a new dryer filter kit, PPV, QR-2, and governor. I hope that those parts fix it. I now have had a week to study the TM's. I made copies of all the trouble shooting pages and the diagrams. I just need some good weather and a little luck. One of the problems I also had while truck was idling, and waiting for tow, was the tranny filter began to leak, it was not even hand tight, 2010 RR rebuild. As others have said RR is a pretty sorry operation. They got the tax payer money for a rebuild, but do little quality work. Thanks for the input.

 

[tstates]

Well just a follow up. Went back up to recover my 931A2. Turns out the purge valve on dryer was hung open due to chunks of foreign matter. I changed out the whole dryer from another truck, and it made air perfectly. Once home, I pulled the dryer apart to find it was a new unit installed in 09. The truck had 300 miles on it since rebuild. Inside of dryer was very clean overall. Once I carefully pulled purge valve out I found about 10 chunks of stuff that made its way through the air system and one got jammed in the valve. In hind sight, it should have been an easy fix with proper tools and an understanding of how the valve worked and came out of unit. Thanks so much for all the ideas.

 

[Triple C]

Glad you made it home, thanks for keeping us updated, it helps folk downstream.