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Thanks, Not sure I understand the circuit exactly but will pull the PPV and see if it's sticking. $20 is cheap enough even if it's not bad. I'm used to buying Ag tractor parts and truck parts are waaaay cheaper. Something like that from Case/IH or John Deere would probably cost $200.

Sounds like your problem was almost exactly like mine but in studying the air circuit diagrams and I'm not sure which valve you mean. There are several and none are specifically called a "priority valve". * Governor valve: 120-127 psi cut out *Compressor Relief valve: 250 psi (unloader valve...

Thanks porkysplace, Downloaded the P2P program.....should help me follow the air circuits. It's looking like part of the problem is a malfunctioning air governor which should limit the pressure to about 125 psi. The wet reservoir pressure relief valve is popping off at about 150 psi. Now...

Note: I pulled the lines off the trailer supply button and I'm not getting any air to the valve. Problem is upstream somewhere.

I have an intermittent problem with the trailer air supply on my M931 Here are my symtoms: When working normally: I have about 125-130 psi on both air gauges and when I press the trailer valve it locks in like it should and the emergency trailer line has pretty much the same pressure as dash...

The trailer wiring socket on my M931 was kind of corroded. I managed to get the pig-tail unplugged without destroying it, but just barely. Got it cleaned up but would like to put some type of grease on it so it won't stick again. I was afraid if I used common gun grease that it might attack...

Thanks for the advice helping me fix the fuel prime problem I was having on my M931. I had to prime the fuel pump each time I started it and it would lose prime within 10 minutes after it was shut off. I replaced all the rubber fuel lines, (6) short hoses on tank selector valve plus supply &...

Thanks, I'll keep those in mind. The local NAPA store ordered one for me for about $35

Looks like I should replace the fuel filter on my M931 as the water drain on the filter canister was plugged. Screwed out the drain valve and found a lot of rusty colored crud blocking the drain. The sticky thread at the top of this forum lists a NAPA 3401 filter as a replacement...

I think I have a basic understanding of air brakes....just has taken a bit to sort out getting military truck working with civilian trailer and making sure everything is working. As far as a CDL goes I haven't gotten one because I didn't have a truck. Now that I have a truck I have a reason to...

It may be that I wasn't holding it in long enough. Seems to take a minute or more to charge the brakes and until it's just about full you can't hear the air moving. Even after the button stays in it takes a bit to get the trailer brake emergency circuit to release. The good thing is the...

I had previously replaced the priming pump o-rings. They were kind of and odd size but found o-rings that would work.

Upon inspection I found that both the supply line & return line at the fuel pump have cracks. Pulled the tank switch valve and 3 or 4 of the six lines there have cracks. There also was a metal return line that had the fitting nut pretty loose....possibly the main source of air leak. While...

Thanks, I'll start checking the suggestions. It's likely something simple but they can sometimes be difficult to find. When I got the truck there was a maintenance sheet that came in the packet. I remember it had a note about the fuel problem but there weren't any details.

Haven't changed any lines or fixed anything other that what I listed above.....looking for a logical place to start.

Well, I checked the lines (not plugged) *Checked the trailer brakes by hooking up to shop air (they worked properly) * Put pressure gauge on service brake hose & emergency hose (got pressure to both) * Checked trolley valve operation with gauge (got variable pressure with lever position) What...

In addition to the air brake problem I posted earlier, I have a problem with the fuel system not holding prime. Before starting the truck I have to bleed the air out of the fuel lines with the hand priming pump. Once I do that it will start right up and run fine. If I shut it off for 10...

Good point....I should remove the coil hoses and make sure they're open, as well as apply air compressor air to trailer lines to see if brakes operate.

Swapped the trailer hoses and it locked the trailer brakes until I bled off the trailer air tank so they must have been right the in the first place....swapped the hoses back. -------------- The valves do seem to operate backwards (lever 90° to line is open) If I close the valves (lever in...

Hooked my M931 up to my new-to-me lowboy to see how it's going to work. Maybe I'm doing something wrong, but I can't seem to get any air to the trailer. First thing I thought was that the valves were off at the supply hoses, but it wasn't the case. The air button below the dash to charge the...