Who did this to my LMTV MPU!

[MrMikey4026]

Somebody replaced the transmission. This is what happens when it is not removed for transmission replacement or not adjusted correctly when it is installed (the hair growing on it is the wire coil inside). I bet my winch tach will work now! MSP6724, ebay 25$
It is located on the flywheel housing, top LH side. Resistance should be about 1440 ohms, this one was something more than that.

 

[coachgeo]

View attachment 823871Somebody replaced the transmission. This is what happens when it is not removed for transmission replacement or not adjusted correctly when it is installed (the hair growing on it is the wire coil inside). I bet my winch tach will work now! MSP6724, ebay 25$
It is located on the flywheel housing, top LH side. Resistance should be about 1440 ohms, this one was something more than that.

ohh..... that is hair growth?? looks like spill of rust particles on a white carpet... was thinking someones wife is going t be reallllll pissed.

Hmm... hair grown...... sooooo...... maybe if you send me that one and I put it next to my pillow at night it will help my hair grow??

 

[Awesomeness]

View attachment 823871Somebody replaced the transmission. This is what happens when it is not removed for transmission replacement or not adjusted correctly when it is installed (the hair growing on it is the wire coil inside). I bet my winch tach will work now! MSP6724, ebay 25$
It is located on the flywheel housing, top LH side. Resistance should be about 1440 ohms, this one was something more than that.

How did you know the resistance should be 1400 ohms? There was a thread here several years ago where people were discussing how to check if it was good/bad, but nobody had any concrete ideas/evidence.

 

[MrMikey4026]

I found the troubleshooting in the TM's.

 

[Awesomeness]

I found the troubleshooting in the TM's.

No kidding? I remember looking in there for a while, back when that thread was around, and coming up empty. I'll have to check again.

Good find!

 

[MrMikey4026]

New MPU installed and the tach works!

 

[Awesomeness]

New MPU installed and the tach works!

The manual says what? Screw it in until it stops, then 2 turns out? It worked first time at that setting?

 

[MrMikey4026]

Actually, I did not look at the TM for install instructions. When I worked as a generator tech, we used the same type MPU's. As I remember they were line up a tooth, bottom lightly and back out 3/4 to one turn. I went 3/4 turn. Same kind of flywheel housing, ring gear situation.
Tach is very steady, I have seen a few videos of LMTV/FMTV tach's that were not.

 

[Ronmar]

They will sometimes pick up ring gear shavings that will make them less sensitive, too far out will of course give a weak signal, and sometimes they just loose sensetivity all by themselves. Had one on my tractor that did that, tach started acting twitchy, checked the position and it was OK and it was clean. Replaced it and worked fine after that...

 

[MrMikey4026]

Ron
You should see how they act when the fail on a one megawatt generator when they fail.
The governor control goes nuts. Scared the dogwat out of me.
You have probably experienced that?
Mike

 

[Awesomeness]

I found the troubleshooting in the TM's.

For those looking, it's in TM 9-2320-365-20-1, e14. TACHOMETER DOES NOT OPERATE OR IS INACCURATE, page 2-348 (p516).

 

[MrMikey4026]

For those looking, it's in TM 9-2320-365-20-1, e14. TACHOMETER DOES NOT OPERATE OR IS INACCURATE, page 2-348 (p516).

Yes, I think it was about a dozen pages, very cryptic without an electrical schematic.
If there is a schematic in the TM's, I never found it. I got lucky and checked the MPU first.
I always hated military technical manuals, they have not improved in the 43 years since I got out.

 

[Ronmar]

There is a schematic in the back of each manual, they are right before the change forms and metric conversion chart(about 7-8 pages in from the back)...

These are layed out in a linear format though but separated by vehicle location, so a single circuit can jump thru several pages spread throughout the 43 page schematic depending on where the circuit actually runs on the truck...

 

[Mullaney]

There is a schematic in the back of each manual, they are right before the change forms and metric conversion chart(about 7-8 pages in from the back)...

These are layed out in a linear format though but separated by vehicle location, so a single circuit can jump thru several pages spread throughout the 43 page schematic depending on where the circuit actually runs on the truck...

I would dearly LOVE to have real drawings that we could print. Would be thrilled to print real blueprints if somebody has something better than the TM for the source.

- Tim

 

[Guyfang]

On a gen set, the MPU should give you about 2.5 to 3 VAC. Thats right, AC voltage. Un plug the MPU and set your multimeter for ohms. Hook the leads to the MPU plug, and then start the truck. Or turn it over anyway. You should get about 2.5 to 3 VAC. For most gen sets, the closer to 3 VAC, the better.

 

[Ronmar]

I would dearly LOVE to have real drawings that we could print. Would be thrilled to print real blueprints if somebody has something better than the TM for the source.

- Tim

You can print them from the PDF manuals found here on SS, I printed them out once When I was learning some of the systems. But being in a linear format, they lay out end to end. If printed on 8.5 X 11 letter sized paper the 34 pages of just the electrical portion would be 31’ long...

I extracted just the drawings into a separate .PDF and did a little editing to get the file size down as low as possible so it loads and pages pretty fast on a my Ipad. I find that the easiest way to use them now as I can rapidly flip thru pages to follow a circuit. I still find my self occasionally writing down coordinates for where the circuit next appears on a drawing as going back and forth sometimes gets confusing... I was starting to draw out individual circuits but have had other things to do lately...

 

[B-Dog]

I was starting to draw out individual circuits but have had other things to do lately...

Were you doing this in CAD or on paper?
An all encompassing schematic would be awesome or it could just be too cumbersome. It's possible to export layers from Autocad to a PDF and Adobe reader is able to turn on/off layers so that might help make things more manageable. You could have separate layers for power/charging, lights, engine, dash; sky's the limit.

31' of schematics sounds daunting....

 

[coachgeo]

... 31' of schematics sounds daunting....

appears they are also not all on the same scale.... some are exploded/shrunk larger than others.... so even if you printed them all and tried to make a wall map of them for example...... it won't work...

 

[Ronmar]

Were you doing this in CAD or on paper?
An all encompassing schematic would be awesome or it could just be too cumbersome. It's possible to export layers from Autocad to a PDF and Adobe reader is able to turn on/off layers so that might help make things more manageable. You could have separate layers for power/charging, lights, engine, dash; sky's the limit.

31' of schematics sounds daunting....

When I was just learning the circuits(while waiting to pickup the truck), I sketched them out by hand, which gave me the idea to simply draw an autocad drawing that incorporated my individual system drawings(Start-run, charging, lighting, brakes-signals, inst ect) I could get quite a few of those on a D sized print(24X36). Unfortunately I just don’t have the time right now. With the exception of the transmission, which gets a little convoluted, all these circuits are pretty straight forward.

In playing with it to make my hand drawings, I discovered I can manipulate the 31’ of electrical drawings pretty fast on my Ipad, so my initial interest in re-drawing them has kind of waned...

Each sheet is 10 sections so to go from location B-148 to C-45 is 10 swipes down. The hard part is remembering what location I am going to-coming from, so sometimes I write those down so I have a chain of locations in the drawing for a particular circuit.