M1083 air brake issue question

[Suprman]

I have a M1083 truck with a brake/air issue. Not quite my area of expertise and I could not find my specific issue in the TM troubleshooting. The brakes do function and the truck can be driven, but when I step on the brake pedal, air flows out the front blue service air gladhand at a decent rate. Regardless of the dash brake control valve or trailer valve position. I replaced the check valve behind the bumper with no change. I was thinking tractor protection valve but I thought it didnt get air unless the dash brake release was pushed. Usually when the tractor valve is bad air leaks out of all the gladhands. I am also wondering of the treadle valve could be bad and air is leaking thru it somehow. Since it always has air regardless of dash valves. Any input would be appreciated.
Will

 

[Oxyacetylene]

Have you checked the other 3 two-way check valves mounted behind the driver's side step? I'm just thinking of valves to check, and those aren't too bad to get to.

 

[Suprman]

I have made some progress. Re-reading the TM it talks about a quick release valve. The only quick release valve that I know is part of the ctis. Which I previously tested by switching to a lower tire pressure setting. But evidently there is also a quick release valve thats part of the service brake system its behind the bumper towards the drivers side. I took one off my parts truck but then it started to snow and I gave up for the day.

 

[Andyrv6av8r]

I have made some progress. Re-reading the TM it talks about a quick release valve. The only quick release valve that I know is part of the ctis. Which I previously tested by switching to a lower tire pressure setting. But evidently there is also a quick release valve thats part of the service brake system its behind the bumper towards the drivers side. I took one off my parts truck but then it started to snow and I gave up for the day.

Look underneath the windshield washer bottle area; I think you will find it there. I had the same issue with my truck and remember taking that valve apart to clean it. It fixed my problem.

 

[Suprman]

We shall see in the morning. Weather permitting.

 

[Ue413]

I had a similar problem, and after looking at almost all of the check valves, no change. I checked my air dryer, which was full of goo and changed desiccant, etc..

Not it sure what happened, but problem went away. I attribute it to air dryer, but who knows. I know I drive / use it much more regularly than what it had seen for quite some time, so maybe that is also a help....

good luck!

 

[Suprman]

No go on the service brake quick release valve. Swapped it out and it still leaks out the service air gladhand with brakes applied

 

[73m819]

There should be NO air coming out of EITHER front glad hand, they are for air during towing ONLY, try turning the one way check valve around.

 

[Suprman]

I dont think the check valve can be installed backwards its male/female. I am wondering if I have a hole in a service brake diaphragm or if air is going thru the treadle valve. Does the tractor protection valve have air supply to it if the spring brake dash control is not released?

 

[KRedd]

Have you checked the schematics in the TM's ?

 

[Suprman]

The tms dont appear to have a complete schematic that I have found. Just alot of flowcharts for troubleshooting.

 

[MGKMartin]

Did you check the two-way valves under the cab on the drivers side? One controls air for the front brakes and the other the rear brakes. They allow air to pass into the brake system when air is applied from the glad hands and prevent it from escaping out the glad hands when there isn't air coming in. One of mine had a tear in the rubber valve and it allowed air to escape out the front glad hand when ever I pushed on the brakes. When I held the brake peddle down, I could hear the air escaping and saw a significant drop in pressure on the front air gauge. Rebuild kits are available from NAPA for ~$15

 

[f8617]

perhaps this is helpful:
my m1078 completely lacked brakes on the rear axle. a ~1oz dose of wd40 in all 4 air brake chambers for both service and parking sides (thru hoses connections) freed it after setting 1-2 days. Some days later i dumped the wet tank without dumping the two brake tanks (until 15-30minutes later) which somehow triggered a venting (a delayed event i heard) and then air leaks thru both front & rear quick release valves that caused the tires to deflate slowly over night...that was fixed either by repeatedly adding air into the tires or by adding wd40 into the wheel valves and quick release valves....both faults seemed to have been solved by cycling out and/or dissolving debris/corrosion.

 

[Suprman]

Are you referring to the 3 check valves that look like 3 way splitters? I will have to take them apart and see whats going on in there too.

Did you check the two-way valves under the cab on the drivers side? One controls air for the front brakes and the other the rear brakes. They allow air to pass into the brake system when air is applied from the glad hands and prevent it from escaping out the glad hands when there isn't air coming in. One of mine had a tear in the rubber valve and it allowed air to escape out the front glad hand when ever I pushed on the brakes. When I held the brake peddle down, I could hear the air escaping and saw a significant drop in pressure on the front air gauge. Rebuild kits are available from NAPA for ~$15

 

[Oxyacetylene]

Are you referring to the 3 check valves that look like 3 way splitters? I will have to take them apart and see whats going on in there too.

Yeah those are the ones I was referring to in post #2. They are Haldex KN25060. The rebuild kit is Haldex RN11V. Not sure if that could be the issue, but I would recommend checking them either way as they all fail at some point. It's just a rubber diaphragm inside.

 

[KRedd]

TM9-2320-366-20-5 w/c3, Figure E-18, Pneumatic and CTIS schematic.

 

[MGKMartin]

Yes, this is what I was referring to. One of mine had a tear in the rubber diaphragm. Like Oxyacetylene said, I used Haldex rebuild kit RN11V and it fixed the problem. Quick and easy fix.

 

[Suprman]

Out of the 3 check valves by the washer bottle, first one was ok. Middle one had a cracked diaphragm. Took one off my parts truck, verified the diaphragm was good and swapped it in the bad ones place. Still have the same problem. Tomorrow I will pull off the last one.

 

[Radiogeek99]

I checked my copy of tm9-2320-366-20-5 w/c3 and it does not have figure E-18. Can someone post a copy of it or pm it to me? Thanks, John

 

[KRedd]

TM9-2320-366-20-5 w/c3, page 1127, Figure FO-2. I apologize for the wrong figure number.