??M929A2 Don't Compress Air With Bed Up??

[gottaluvit]

M929A2 Don't Compress Air With Bed Up?

1.) So today between the rains I was lubing my newly acquired dump truck and had the bed up to access more and let light under. I wanted to move forward an inch or so to gain access to the u-joint grease fittings on the propeller shaft between the transmission and the transfer case. I couldn't get the air up enough to release the brakes and as I pumped them it dropped and wouldn't gain any pressure. So I thought they might have over-safetied the truck so it wouldn't build air to move with the bed up and maybe that is what that funny hook looking thing in the center of the frame is for. Lowered the bed and it aired up the tanks. Really?? Who comes up with this stuff? Or is it not meant to do that and there is an issue?

2.) Also, back in the day of being a driver of an M817 dump, I was a pro at spreading gravel so well that the grader operator had nothing to do when I dumped gravel as a REP platoon driver at Wielflecken, West Germany. With this box of safety I now have, I have to put the trans in neutral before the pto operates, even though I have to put it in 1-5 to engage the pto. So (to seasoned M929A2 operators) how do I spread gravel with this truck?

 

[gottaluvit]

Okay, so I am flirting with coincedence. Went to start truck today and it isn't building any air pressure. The crazy thing did start building immediately yesterday after I put the bed back down and now with it down it won't build a pound of air. Going to get a new air dryer as that is cheaper than rebuilding. Could there be something else that could be the culprit? I don't mind putting a new dryer on anyway but what other possibilities could be out there?

 

[dawico]

Unloader sticking or compressor out. Search for threads on how to test those.

You could have a major air leak too. Also threads on how to test that.

 

[Swamp Donkey]

Was the air dryer constantly blowing out the bottom? If the purge valve got stuck maybe the bed coming down jarred it enough to close it back off. Just thinking out loud here...

 

[gottaluvit]

Well, with it so rough looking I felt a rebuild or replace was in order anyway. The jarring was the conclusion I came up with too

 

[gottaluvit]

I finally got a break on the rain so I decided this evening was a good time to root around under the truck. With it running I couldn't hear any air leaking anywhere, even though it is a challenge to block out the noisy cummins. I took off the inlet line that goes to the dryer and no air whatsoever coming out. I do hear a ticking sound that sounds like it is coming from near the left fuel tank but it is very hard to narrow it down to exactly where. So I followed the main out of the compressor and it has nothing between it and the dryer except a safety blow off valve and no air leaking there either. Surely the compressor didn't work perfectly and then just fail upon my next start up of the engine, did it? What could make a gear driven compressor fail anyway? I felt all around it for leaks and feel none, so I don't think it would be a head gasket. I know the gear drive is working as it looks as if the power steering runs on the same drive and it works very well. Searching on here brings up the craziest non relevant stuff so that is kind of out on this subject. Anyone have any links to relevant threads? I would really appreciate some help on this. Kind of an expensive lawn ornament at the time. Has a nice message though.


Jim

Oh yeah. It did fail to air up a couple of days ago as I had the bed up and then started to work immediately after lowering the bed. Thought it was good to go until the next day with no air at all (bed down).

 

[Ddmk18]

Sounds like the unloader in the compressor or the top basket on the compressor. Mine did it so I changed the top gasket on compressor and cleaned and lubed the unloader. Its been good ever since

 

[gottaluvit]

Sounds like the unloader in the compressor or the top basket on the compressor. Mine did it so I changed the top gasket on compressor and cleaned and lubed the unloader. Its been good ever since

That is the route I will take as soon as the rain lets up (if it does at all today). I went out to start but that break didn't last long.

As for the TMs, well, so much for accuracy...again. I have a different air compressor and different governor than what they have pictured. TM said all models but my gov has three inputs/outputs for air and the compressor has the supply line in the front and none in the back as pictured. They show a hose going to the governor and I have a steel line hugging the engine and then a hose from back of engine to the governor. I also have some plastic cover looking thing on the governor and the adjustments are not visible as shown in TM image.

So is the two bolts that go straight down from the top (with the skinny steel line attached to a round disc held down by them two bolts) what holds the unloader or is it the two outward facing bolts that hold some odd looking thing that has the fat short hose attached? Or should I just remove everything from the top of the compressor and know I had to get the right thing if I got it all cleaned and lubed with dexron? The fat hose goes into the side of the engine after exiting the compressor, but I have no idea what that is as the tm completely left all that out of the diagrams. Any help turning my oversized, overpriced yard decoration into a working truck would be greatly appreciated.

Jim

 

[dawico]

That is the route I will take as soon as the rain lets up (if it does at all today). I went out to start but that break didn't last long.

As for the TMs, well, so much for accuracy...again. I have a different air compressor and different governor than what they have pictured. TM said all models but my gov has three inputs/outputs for air and the compressor has the supply line in the front and none in the back as pictured. They show a hose going to the governor and I have a steel line hugging the engine and then a hose from back of engine to the governor. I also have some plastic cover looking thing on the governor and the adjustments are not visible as shown in TM image.

So is the two bolts that go straight down from the top (with the skinny steel line attached to a round disc held down by them two bolts) what holds the unloader or is it the two outward facing bolts that hold some odd looking thing that has the fat short hose attached? Or should I just remove everything from the top of the compressor and know I had to get the right thing if I got it all cleaned and lubed with dexron? The fat hose goes into the side of the engine after exiting the compressor, but I have no idea what that is as the tm completely left all that out of the diagrams. Any help turning my oversized, overpriced yard decoration into a working truck would be greatly appreciated.

Jim

The two bolts on top hold a round cap in. That is the unloader. Someone told me to take the line off it and put a few drops of transmission fluid in there to lube the unloader. I didn't try that though as the advise was late. I had already rebuilt my compressor and unloader.

Another member had the spring inside there break. If you pull the line and loosen the two bolts on top of the unloader an internal spring should push the cap up to the IP (once you break the cap free). If not the spring may be broken.

The two bolts facing you hold on the intake.

When my compressor wasn't working I hooked up a gas air compressor to one of the glad hands to get it home. By the time I got home the compressor was pumping again. This actually happened twice before I tore it apart and rebuilt the unit. My compressor was leaking pretty bad so it was the right thing to do anyways. No problems since. I cleaned and lubed the unloader valve while I was in there.

 

[gottaluvit]

Late advice here too. I went out and tore the top off that thing. Had me furious at the wannabe engineer who didn't think to leave that extra 1/4" space. I had black water in the line to the unloader. It was indeed stuck. Very stuck. Gonna clean it all up and use the dexron for lube and hope to put it back together. I had to pull the back bolts up and out with a "well" engineered coat hanger having a special bend to hook to them bolts. Can only imagine the bad talking them non engineers I will do on reassembly.

 

[dawico]

Yuck, but not surprising. Sounds like you found the problem.

Yup, blow out the line, clean it all, and lube it up. Should be good as new.

I found that when I rebuilt my compressor I had to adjust the governor to get the air pressure right. I cut my own gaskets from a sheet so I could get it going again.

 

[Coffey1]

Yes getting those two bolts in the back under the IP it a royal pain the ass to get out and back in
Also rub the head against some sand paper and see if head is true if not it will blow head gasket.

 

[gottaluvit]

I plan on making this item part of regular maintenance so I don't have to mess with it again. When I break out the grease gun it is time to take that intake cover off and blast some wd as well as a little shot of dexron and also remove the line on the unloader valve and shoot some of both down in there too.

I do have one more question regarding this. My gasket for the basket that the unloader is mounted on has a nice sealing surface but is a bit deteriorated where it makes no contact with anything. Is this going to be alright, and if not where do I acquire a new gasket?

Thanks,
Jim

 

[Coffey1]

Cummins has the parts.

 

[gottaluvit]

Will they know the model number of the compressor by what truck it is on or do I need to know the number of the compressor beforehand? If so, anyone know the model number? Can I order online or a specific big rig dealership?

 

[Coffey1]

Get the number off the head and I'll check with my buddy and see how he told them what he wanted.

 

[gottaluvit]

Ok. Awesome. Thank you.

When it unloaded in the past it did make a very strange sound in doing so and not sounding like a regular semi truck. Is that normal or a sign it is starting to go. These MVs with full air are new to me. Had juice brakes and air for something but not full air back when I drove the old 5 ton back in the 80s.

 

[Coffey1]

When that head gasket let's go you will know.
Scared the crap out of me . It was a loud pop then air started dropping like a rock.

 

[dawico]

Ok. Awesome. Thank you.

When it unloaded in the past it did make a very strange sound in doing so and not sounding like a regular semi truck. Is that normal or a sign it is starting to go. These MVs with full air are new to me. Had juice brakes and air for something but not full air back when I drove the old 5 ton back in the 80s.

Mine makes a clicking/ tapping sound when pumping. Others have said the same.

 

[Coffey1]

Most likely the unloader bouncing on that spring.