Air brake question

Thought I would consult the vast knowledge base here.....Heres the problem - when the air brakes are released air leaks from the emergency gladhand in the front of the truck. is this normal for that to be charged with air? If not then what would likely cause this?

Yes it has air to it.My 923 has cut offs. Are they leaking before cut offs .
One of mine was leaking had to replace the cut off valve.

The front glad hand should have a hole in it to release air , so yes this is normal

The front gladhands are for input air only. the yellow to apply the (towed) truck brakes. And the red to charge (the towed truck) air tanks. And so they have one way valves to stop the outflow of your trucks air supply. Whichever one of these on yours is leaking wants servicing or replacing. Likely, if the leak is when the brakes are applied / released then its the yellow.

Its leaking from the one marked "emergency" and red in color.

That's the one that was leaking on mine just put a new ball valve cutoff on it.
Problem solved.

Crap I was wrong , I thought the front right .... Never mind . You learn somthing new everyday

Coffey1 - I was hoping that might be the problem - I will try that first

Rmtaunton said:

Crap I was wrong , I thought the front right .... Never mind . You learn somthing new everyday

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At least your learning something new everday. Me I seem to be forgetting something old everyday.

tokarev said:

Thought I would consult the vast knowledge base here.....Heres the problem - when the air brakes are released air leaks from the emergency gladhand in the front of the truck. is this normal for that to be charged with air? If not then what would likely cause this?

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Which FMTV do you have? The LMTV like mine does not have a cutoff valve for those front gladhands. Both the emergency and service have vented caps on the covers, so they are not supposed to be sealing them off either. I actually have this exact same problem with mine which I have been very lazy and have not fixed yet, ha ha. In some of the literature online, it warns not to just plug or block off the front gladhand if it is leaking air....but I did anyway. The warning states that it may interfere with the emergency/parking brakes being applied, but so far it hasn't on mine. I replaced the one check valve that is right below the emergency gladhand on the other side of the T fitting, but that didn't fix it. It has to be a one way or two way check valve somewhere else that is malfunctioning. On mine, I disassembled the emergency gladhand fitting and behind the metal screen there were small pieces of plastic or hard rubber, so I am thinking that a valve somewhere is messed up and chunks of the diaphragm were blown all the way to the end of the line.

I just resolved an issue on the FDT where air exhausted the front emergency gladhand with the system park released.
Though the TM points to the bottom 2 way check valve of the 3 behind the driver's step, the top 2 way check valve was the one that ran directly to the gladhand. Once it was replaced , all was good with the the system.

Any pieces of rubber against the screens of the gladhand would probably be pieces of the next check valve upline.

DSD277 said:

I just resolved an issue on the FDT where air exhausted the front emergency gladhand with the system park released.
Though the TM points to the bottom 2 way check valve of the 3 behind the driver's step, the top 2 way check valve was the one that ran directly to the gladhand. Once it was replaced , all was good with the the system.

Any pieces of rubber against the screens of the gladhand would probably be pieces of the next check valve upline.

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I need to get back to troubleshooting mine too. This sounds like a good place to start. Thanks! OP - been a few days since the posting, have you fixed yours by chance?

Oxyacetylene,
Remove the front grille and trace the large air hose from the E gladhand back to the backside of the driver's step. Remove that air line from the 2 way valve. If air comes out, you found your problem.


I have learned to keep a few of those 2 way valves around (they're cheap and rebuildable), along with some extra fittings , air line and plugs/caps ( for testing ).

Air brakes are actually fun to work on. With the TMs and an open end wrench, you can usually find the problem by cracking air line open at fittings to see if air is where it suppose to be or not. And no **** fluid to deal with and make a mess of everything.

I hope this isn't considered "high jacking" on Steel Soldiers as its in the same general topic. I've got an air brake issue as well, but a little different. When I apply the brakes, they all engage. However, air releases out of the bleeder valve on the trailer protect valve. I did have to replace both check valves above the drivers front tire. So, I thought maybe I had crossed a line or something. But after double checking, the connections appear good. Any thoughts?

I was messing with mine today first trying the check valve below the glad hand - didnt work still leaks just as DSD277 mentioned - DSD277 is the check valve that caused the problem on your truck is located under the dash?

tokarev said:

I was messing with mine today first trying the check valve below the glad hand - didn't work still leaks just as DSD277 mentioned - DSD277 is the check valve that caused the problem on your truck is located under the dash?

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The 2 way check valve is located on the back of the panel behind the washer reservoir (left side, behind the step). The valve is the top one of the 3. If you remove the front grille and trace the air line from the E gladhand through the tie wrapped bundle on the left side. Cut the tie wrap and verify the hose all the way to the check valve, and save yourself some possible grief.
I just looked at the TM and it points to the bottom check valve for the e gladhand. I know that isn't the one on my truck, but the top one.
Tilt the cab and check valve is right there.

The one way check valve goes back to air tanks ( or so the diagram says)
.

Bingo she is fixed - I replaced the double check valve - the first one up the line from the emergency glandhand. Bought the replacement valve from the local Fleetpride location for $27.19 PN AV278614. Ready for the Florida Rally in March.

Glad you found problem when I first posted my bifocals did not pick up that it was FMTV thought M923.