M915A1 Trailer Air Supply Valve Operation

[Tow4]

Reading through the M915A1 -10 TM, I see the tractor parking brakes have to be released before the trailer air supply valve can supply air to the trailer. I did verify that mine works this way. I imagine either the military had this requirement, or that's the way trailer air systems worked in the '80's.

I know modern civilian tractors can supply trailer air without releasing the tractor parking brakes. This makes sense, because if the trailer air tank is empty, it can take awhile to pump up.

I want to be able to supply trailer air without having to release the tractor parking brakes. Before I get into the air system diagrams to figure it out myself, has anyone here updated the air system to work this way?

 

[Castle Bravo]

My M916 is this way as well. It would be nice to be able to do a walkaround or whatever while the trailer is airing up instead of having to sit in the cab with your foot near the brake.

 

[jatonka]

I think the same thing every time I pull out of my yard with my 915A1 and lowboy.

 

[Monkeyboyarmy]

How about charging both systems and then pull on the trailer hand brake to hold it from rolling? Then you should be able to check 3 of the 4 systems.

 

[Tow4]

After looking at the air system diagram, I think I have it figured out. I have to look at the truck to be sure, because it's a little different from the air system diagram in the -20 TM. I'll post up when I'm finished.

 

[wreckerman893]

How about charging both systems and then pull on the trailer hand brake to hold it from rolling? Then you should be able to check 3 of the 4 systems.

It is a very, very, very, very bad idea to use the handvalve as a brake. If you are on the slightest incline and the lever releases the truck will roll. I had to Article 15 one of my soldiers for habitually doing that. His luck ran out and a M916 with a dozer rolled across the Motor Pool and hit another parked trailer. Do not do it.

 

[Monkeyboyarmy]

I would think that you would pull on the trailer with the tractor while the brakes are on to see if it would hold it. I'm used to wet clay around here where nothing moves without 6x6.

 

[Castle Bravo]

After looking at the air system diagram, I think I have it figured out. I have to look at the truck to be sure, because it's a little different from the air system diagram in the -20 TM. I'll post up when I'm finished.

Did you ever get around to this?

 

[quickfarms]

This was common for the operation of some commercial trucks.

We just chock the truck while the trailer is airing up.

 

[Tow4]

Did you ever get around to this?

Not yet, but I have determined the MV-3 valve stems will fit through the holes in the dash. I would have to drill holes for the mounting bolts.

The other option is to add a PP-7 and make it a three control valve system. I have all the valves to do it, I just need to decide which I would like better.