LMTV M1078 Tachometer

Yeah, a tooth count, just what I was looking for. All my trucks are cat 3116 mechanical. So do you have a cat 3126 or 3116, I would assume 3126, hope fully the flywheels are the same but I believe the 3126 is a 7.2 liter and the 3116 is a 6.6 litre. Thank you so much for that reply, and when ever you get pics up that would be awsome as well, love to see the guts!

I think they are both 6.6 litre. The 3126 is just the electronic fuel injection version.

It seems to be the standard for diesels is a magnetic sending unit off the flywheel, the sending unit reads the pulses per revolution. We have a custom cummins 4bt diesel project we are doing and it needed a tach as well. I was suggested a altinator style tach and wasn't impressed with the type of install or results so I ended up going with this style which seems to be the norm, the magnetic sending unit by flywheel is how the trucks are geting the tach reading now, I believe.
So I bought two types of sending units, a single and a dual output, well see which one is gonna work best. I figured using the dual output to supply the transmission and the new tach, if it starts to pose a problem I'll leave the original magnetic unit in and set the new single in the second port of the bell housing which is a vent. I'll just vent some other way by drilling and tapping, the bung is already drilled and tapped for the .75 x 16tpi unit. Stay tuned, I'll be wrapping this up asap and getting into a Pyro and boost guage next, still doing research on the best quality units for diesel applications. I think it's crucial to have all the guages that tell you what ur engine is doing and how it's feeling. I think then I'll start the research of the difference between a 225hp 3116 and a 290hp 3116, both are mechanical, the m1078 has 225hp, and any m108 or m1083 has 290hp, basically any 6x6 has 65hp more than a 4x4.

Ok figured out how to post pictures. Here is the lift bracket I fabricated and another pic of the flywheel.

Awsome Keith, thanks for those pics, so is this the 134 tooth flywheel?

Yep, thats the beast!

Hi Keith, that's a great looking lifting bracket , you've designed

Thanks but I found the design and dimensions in the tech manual.

Suprman said:

View attachment 606747

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according to pdf quoted above, Refering to socket P901 which goes to tach. Seems that Pin 4 is a + power source. Not sure if it is 12 or 24v though. One pins wire logically has to go to the magnetic pick up at the flywheel as well. Guess in testing one of the pins will result in a pulse, if a multi meter could read it fast enough. Not sure if one can see such a fast pulse with a mulit meter though. Never tried.

This pdf of a diesel tach is of some help too. Looks like 4 wires in harness to P901 should be signal, ground, ignition power source, and power for light (from lights switch?)



Has anyone traced the pin out on P901? this info would help anyone adding a tachometer. Is it 24v or 12v Tach, guess one could tell by voltage of Pin4? I'll keep searching and post this info if someone does not pop up with it before I find it.



PS- note the selector on back of tach for tooth count of flywheel. Denoted as a left facing arrow.

Lmtv772 said:

My LMTV (with winch) doesn't kick up the RPM , you have to raise it via the hand throttle.

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A1 trucks have a high idle switch for throttle control. No tachometer is needed.

Couple question for you lmtvjunky,
I'm new to this forum, and in the initial phases of researching the m1078. Intended us is to crawl around the Sierras and ultimately mod into an overland vehicle. Can you you offer any insight into registering and emissions in California, I'm based in San Francisco and East Bay. Been looking at Iron Planet, are there other sources that you would recommend? Mike

I am betting that tapping into the factory accessory switch box harness as mentioned would provide the tach signal.... FYI in the diagram of the connectors the round 4 pin 901 connector is for the heater and supplies both 12v, for the heater lights and 24v for heater power.

The troubleshooting tm states which pins to check if there is a problem with the tach that should be a good starting reference.

Suprman said:

The troubleshooting tm states which pins to check if there is a problem with the tach that should be a good starting reference.

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Good suggestion. Have started on that path. My post about pin out quoted one of the service TM's from earlier in this thread which mentioned the tach. So far it's the only one that has mentioned something useful (pin 4 gets + power signal). Additional searching of TM's for other ones that mention the tach have been found but they are the same ones posted earlier here, along with a few others but were not of any help. (or I missed a clue in them). Will keep looking and revisit others.

Thus far attempting to follow wire schematic of connector P901 which connects to tach. Learning as I go so below may have some errors that I will update in this post as a find them:
To follow along ... go to pg 1179 of 3rd book of TM for 1078 (fold out 24 of 34)

Pin one*- inside tach's harness this goes to tach dash light (assume that is internal light of tach) and in truck harness this wire trace is labeled #3020. This follows to plug P913 at pin 10. P913 has a connector to C123 at one end and continues on at point G218 (G21B?) of Schematic on other end

Pin two*- inside tach's harness this goes to tach dash light (assume that is internal light of tach) and in truck harness this wire trace is labeled #1908. This follows to plug P913 at pin 11. P913 has a connector to C123 at one end and continues on at point G218 (G21B?) of Schematic on other end

NOTE- Pin one and two's wires up to this point have another couple stops along the way. Seems most of these are also lights


Pin Three*- inside tach's harness this goes to REV (Revolution counter?) and in truck harness this wire trace is labeled #1546. This follows to plug P913 and terminates at pin 9.

Pin Four*- inside tach's harness this goes also to REV (Revolution counter?) and in truck harness this wire trace is labeled #1550. This follows to plug P913 and terminates at pin 12.

NOTE- Pin three and four's wires up to this point have no connections to other things



*see http://www.steelsoldiers.com/attachment.php?attachmentid=606747 to determine which pin is which inside the connector

Continue from above

Pin one's wires #3020 at connector P913 thru pin 10 connects to TB2-31 (G134) (GI34?) This Y'zs also to PX14A-2 (H112)

Pin two's wires ... #xxx at connector P913 thru pin 11 connects to Personnel Heater motor switch thru wire xxx and either grounds or powers it's dash lights and maybe fan itself?

Got to go. More later, keep getting sidetracked with other projects

Superman I've been searching the web for the Medallion tachometer for the FMTV with no luck. Would you happen to have a part number or description to help me out?
thanks

Suprman said:

The A1 winch truck that I have did not have a tach. I believe this is due to electronic engine rpm control. Less operator options.

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You are correct in A1's the RPM is governed by the high/low idle switch, no tach needed the computer handles it all.

12414345 but its a first gen truck part. No tach in A1. Winch on the computer kicks the idle up automatically as stated above.
Will