m813 service brake connections?

[midcounty]

I have some questions about the operation of the service brake glad hand connections. I was looking at a M813 today, and was thinking of using it to flat tow a M818 that has engine problems. When I went to check out the glad hands on both trucks to see what I would need to hook up the brakes to the towed truck, I noticed there was no glad hand or shut off valve on the rear of the 813. The truck drives ok, brake light and brakes seem to work alright. I put my thumb over the open fitting and hand someone press the brake pedal. I felt a real light pulse of air, but that was it. Is there a safety built in to the system that prevents it from dumping air if the system is open? I just though there should be a considerable amount of air movement there. Any help here would be greatly appreciated.

 

[R Racing]

My XM813 has shut off valves on the rear but the front doesnt because it has a check valve .

 

[midcounty]

Hmmm, there was a fitting there on the rear that I am now wondering about. I wonder if who ever removed the shut off valve placed a check valve there to keep it from dumping air. That could explain the light pulse I felt.

 

[Truckoholic]

I am not real familiar with the way the air brake systems work on these military trucks yet. For what it's worth, I have a certificate that says I am an "Air Brakes Specialist" because of an air brakes training course I went to. ha ha So air brakes on regular trucks, I am very familiar with. If they work similar at all, you will not get air coming out the "Service" gladhand on the back of the truck, until you push in the "Supply" or "Emergency" or "Red" knob on the dash in the cab. When you push that in, it supplies constant air to the supply or emergency gladhand at the back of the truck, AND now allows air to flow to the service gladhand when the brake pedal is pushed so you don't lose all your air every time you step on the brake without a trailer hooked up.

I am completely unfamiliar with what knobs there may or may not be on the dash of these military trucks that would be the equivelent of the "Supply" or "Trailer" knob in a civilian truck.

 

[73m819]

the 54 and 809 series don't have the dash controls, a shut off valve at the rear shuts off the air

 

[EMD567]

On the rear of the 800 series, the supply(red) and service(blue or yellow) have shut off valves. On the front, they may have the valve, but they also have a check valve to prevent over pressure should the engine on the towed vehicle be running.

 

[midcounty]

I am a little more awake now, so let me explain further. I traced out the air lines underneath, and there is no shut off on the service line to the rear, like my other trucks have. There is a fittng that looks similar to a coupler where the elbow is in the rear. I am wondering if somone removed the shutoff valve and glad hand and just put a check valve there as a quick fix to keep it from dumping air while braking.

 

[jimmcld]

I've found that the biggest problem when working on these trucks is that some private worked on it first. We usually assume that everything is hooked up correctly when we get the truck. From my expierence, this is not always the case. Sometimes it takes a lot of head scratching to figure out how it should be instead of how it is.

 

[jwaller]

I am a little more awake now, so let me explain further. I traced out the air lines underneath, and there is no shut off on the service line to the rear, like my other trucks have. There is a fittng that looks similar to a coupler where the elbow is in the rear. I am wondering if somone removed the shutoff valve and glad hand and just put a check valve there as a quick fix to keep it from dumping air while braking.

you need to remove the check valve and reinstall a hand valve or ball valve. that check valve is not going to let enough air out to get the brakes on the vehicle being towed to work at all.