Need Information for Flat Towing M931A2

[ke5eua]

Sorry, you are wrong. It is ONLY releasing the spring brakes, which are held off by air. The service brakes are still operational.

Learn something new. I was explained it the other way, and it stuck. My apologizes.

 

[Mike929]

Thanks for everyone's help. The City has given me another week to move my truck so some of the pressure to move it now has been eased. (i.e., I will defer to my brother on when he wants to do this.)

My brother has picked up two 10' hoses and 4 glad-hands to make up a set of hoses for the flat tow. These along with heavy chains, med. tow bar set, and driving the deuce in low range (which will also limit top speed), should allow us to make the 100 mile trip on relatively flat and straight highway. I will leave the brakes caged as suggested, and go from there.

I have been informed by several, that at these slow speeds putting the transmission and transfer case in neutral is all I need to do. No value added in removing the drive shafts. With this being the case, I'm going to leave the drive shafts installed. No reason to tempt Murphy any more then I have to by removing additional parts.

Brother called around and found a bulldozer 60 amp/24 volt, brush-less w/big bearings. I can't see any downside in abandoning the military alternator with something commercially available and to the best of my knowledge, more reliable and less likely to destroy my truck if it dies.

Present status: Truck will not even crank presently. I do hear a buzzer when switched on, with the reconditioned batteries installed, but I am going to pull all 4 batteries and pick up two red top Optima to replace the two fried batteries and provide a known current. I well then see if there is a trouble shooting section in a TM that walks me through the systems I need to check to track down what was damaged.

I was told that the Electrical Control Box (on firewall in front of driver), is most likely something that died, if I am not getting current to the starter. I know I blew out at least two gauges (hopefully just the gauges and not the wiring). I would also guess all my lights are toast since they were all on at the time (including a trailer), and went out with the Alternator blew.

I will start a new thread when I start working through the mess, and will search through the site to glean as many answers as I can. If anyone sees a problem with my present plan, feel free to tell me, but I feel based on input that this is a solid way forward.

Definitely a rough start to my first experience with the M939A2 trucks.

 

[Mike929]

I already sent him my number wheel spinner.

Thanks for sending me your number and helping me work through what I need to do. Hopefully I will be in a position to pass it forward in the future.

 

[Coffey1]

Mike no problem when I get home I look through the wiring digram and see what I see.
I can try to send you a picture of it if you want it.
It's the complete digram on one page.

 

[98G]

I dont have hoses and didn't realize I couldn't buy them from a truck place, so looks like I will not be able to hook up the deuce's air to the M931a2.

This strikes me as a very bad idea. The 5ton is heavier than the deuce. Pulling It is one thing and stopping it without using the brakes on it is another thing entirely. Stopping it suddenly without warning with even a little bit of turn involved will push a deuce around and sideways in a hurry.

I see that you've changed your mind and intend to hook up air at this point. I post the emphasis for others who may be using this thread for reference in the future.

 

[Mike929]

My brother was able to get a flatbed for his Semi-truck, so we are now changing the dynamic of the conversation. Now the issue is loading it onto the trailer. Worse case is with a come-a-long or high lift jack, but I really don't want to experience that kind of slow painful fun. He has access to it on Friday and/or Sunday so not sure if I can get the truck running in the time available.

I'm going to remove the old batteries dust down the battery box with baking soda and run a hose to wash out and hopefully neutralize as much of the battery acid that evaporated out of the batteries and condensed on the inside of the battery box. Then I am going to install two new red tops. There are two small wires that I am not sure how to wire up. I assume the one that went mid set on the negative term would be on the mid terminal of a two battery system, and the other one would stay with the positive battery cable to duplicate the 4 battery wiring.

I think based off what I've heard I probably burned out the Electronic Control Box (P/N 11669304) that is between the alternator and starter.

Can anyone confirm this?


In the TM it says there is a relay that is reset when the plug is removed, assume that would have reset when I unhooked the batteries and that the box is dead because the starter will not even attempt to crank.

If it cranks after I replace it but it doesn't start, I will look into bypassing the fuel solenoid that may be preventing fuel from getting to the engine.

Any other ideas on how to get it started?

If I don't get it started, I'm thinking of using a rope and my pickup to help drag it onto the trailer.

If there is a better idea, please share, thanks.

 

[ke5eua]

What kind of flat bed, rgn, roll on, step deck, skate board?

What kind of pickup do you have and do you have any snatch blocks, pulleys?

Did you look through the 20-22, it covers some things like this.

Also, there is a way to bypass the black box for emergency situations. I'll see if I can dig up the cheat sheet.

 

[ke5eua]

Got it, post 21 in this thread.

http://www.steelsoldiers.com/showth...-Control-Box&p=1557388&viewfull=1#post1557388

Here is the quote from it:

I had a failure of the PCB in my M925A1 last year. As part of the troubleshooting, I made some notes and took some pictures, attached. Mine was the type with a circuitboard. Hopefully the wiring diagrams will be helpful to someone in troubleshooting. I also put together a little troubleshooting guide, which goes to the extent of taking the box apart and checking the individual relays. The relays can be purchased individually fairly economically. In my case the main power relay was bad. I noticed that that model was an Ametek SAS-4418, which is a heavy duty intermittent relay, only rated to be energized 10 minutes at a time. So I replaced it with a SAS-4410, better rated for the application, i.e. continuous duty, more appropriate for the main power relay. Info at texasindustrialelectric.com.

View attachment 497104View attachment 497105View attachment 497106View attachment 497107

View attachment 497112

As has been noted in other threads, the PCB provides protection against polarity errors and energizing the starter while the engine is running (signal from alternator to Terminal F). In the event of circuitboard failure, it would be pretty easy to rewire the box to bypass the circuitboard and directly energize the relays from the inputs to the box, but then those protections would be gone.


As far as emergency bypassing in the event of failure, you can connect the C & D terminals, the large wires, to replicate the function of the main power relay, then just jumper the starter. You also need to power the fuel solenoid to make the truck run, which can be done with the normal "RUN" switch position on the ignition switch once the main power relay is jumped. Keep in mind that alternator output will go through the jumper so it needs to be substantial. Just for kicks, I made a jumper out of 1/4" steel tubing, stuck it in the PCB plug sockets for Terminals C&D. Ignition switch on, then short the jumper to Terminal B (wire 74) with a screwdriver, the truck fires right up. Just keep in mind the jumper is electrically hot, and be careful handling it especially in the rain; 24 VDC can shock under the right conditions. See picture:

View attachment 497102

It seems the PCB enclosures may be put together a couple of different ways. I cut mine apart with a thin cutoff wheel in a side-grinder, then tack-welded it at four locations and JB-welded the gap all around.

 

[Mike929]

What kind of flat bed, rgn, roll on, step deck, skate board?

What kind of pickup do you have and do you have any snatch blocks, pulleys?

Did you look through the 20-22, it covers some things like this.

Also, there is a way to bypass the black box for emergency situations. I'll see if I can dig up the cheat sheet.

I don't know the technical name but from a layman view point, it has drop down ramps and the deck that is about 3' off the ground.

Pickup is 14 year old GMC, 4 wheel drive half ton. I shifted it into low range and walked the M931A2 about a 100 yards yesterday to get it off the street. I think I can get enough grip to pull it up the ramps if I can set up the rope in a way that allows me to drive in parallel to the trailer. I will probably use my dad's newer (stronger) GMC 4x4 to pull it out of my back yard, since my truck is trapped back there presently. If only I had a Prius.

I've mainly been looking at the trouble shooting sections to figure out what parts I need to make it run, but didn't know about a bypass for the black box. It only needs to drive up the ramps and off when we get there. Having power steering would and air would also be huge improvements.

Is that procedure in the TM's?

(Just saw your response reading it and linking to the thread you found now.)

 

[ke5eua]

Check my previous post. I copied the post from another thread. It has the diagram about bypassing it. If you can get it started that would be the best option. Trying to pull it on the trailer will strain your truck unless you use three snatch blocks and have 300' of rope.

Snatch blocks will be your friend if you have to pull it up the ramps.

 

[ke5eua]

Oh, the technical term would be step deck most likely.

Look something like this?



Getting it up the ramps is going to be the challenge.

Now instead of trying to pull it up, have you considered pushing it with the deuce? That would honestly be a better option than using a 1/2 ton, even pulling it with the deuce as it is heavy and has more torque and ground pressure.

 

[Mike929]

That looks like the trailer I've seen him use before.

My truck did well moving it up the drive way, which has a slope and over a curb into my back yard. Main issue was after I got everything on grass and tried to pull it up the slope of my backyard. The tires on my truck started slipping so we called it a day.

So to bypass the black box and start the truck, I just need a large jumper for C and D at the rear of the plug, then turn on the Battery switch and the start switch to run, then have second person short from terminal B to the jumper, and the truck should start (if the box is the issue.)

I have disconnected the alternator but assume the battery power is also going through the jumper.

 

[ke5eua]

How did you disconnect the alternator?

If you just removed the main wire off of it make sure you tape it good so it can't arc.

Try to get it started, if you can just drive it up the ramps, if you can't start it I would recommend using the deuce for the obvious reasons.

Yes your half ton will pull it, a Prius will pull it, lol but what you need in this situation is weight and torque. Both of which your half ton can not compare to the deuce.

Is your brothers semi setup for a mfn lowboy, if he is he will have a drag winch on the rear of his truck.

 

[Mike929]

I disconnected all the wires, including the ones under the box w/ glue coating. They are all taped up and separated. That alternator hates this truck, I don't want it doing anything but holding the belt until I can remove it and replace it with a commercial Bulldozer alternator.

No winch on his truck, just a normal truck and flatbed that they move stuff from point A to point B and off load with other equipment.

 

[Mike929]

Added 4 new group 65 batteries and it started right up. We quickly discovered the blown gauges were shorted and pulled the dash to unplug them, kind of obvious in hindsight.

Backed it up onto the trailer, chained it down and drove it to my brothers. I was very happy not to have to tow/winch it onto the trailer or off of it. On a side note is there anyway to stop the loud horn type sound when you engage the brake and the truck dumps air into the intake stack? It is extremely loud and wasn't just happy I had to do it at 1am in the morning at my brothers.

Thanks for all the help and advice.

 

[ke5eua]

Glad it started up.

The buzzer is located under the dash on the drivers side against the side wall.

 

[Mike929]

Glad it started up.

The buzzer is located under the dash on the drivers side against the side wall.

Not talking about the buzzer. It is like an air valve dumps the air tanks into the air intake stack which makes a an awful wailing noise, like a dieing pipe organ. This is after the truck has been running and pressurised the system and you shut it off and engage the parking brake

 

[ke5eua]

Not talking about the buzzer. It is like an air valve dumps the air tanks into the air intake stack which makes a an awful wailing noise, like a dieing pipe organ. This is after the truck has been running and pressurised the system and you shut it off and engage the parking brake

Don't know about that one sorry.

 

[Mike929]

Don't know about that one sorry.

No worries.

 

[VPed]

I think the sound you are hearing is air from the spring brakes. When you engage the parking brake, you release air from the spring brake chambers, causing the spring brakes to set. The sound you hear is that air as it is routed to the intake pipe. The regular service brakes take air pressure to apply but the spring brakes take air pressure to release. That is why you cannot drive off without first building air pressure. The sound it makes can vary from truck to truck, dying organ, someone stepping on a duck, a goose with a cold, etc.

There is also what is truly called the parking brake. that is a mechanical drum brake on the driveline. it works together with the spring brakes when you use the parking brake lever as long as the spring break override button is not in the override position.