Versions of HMMWV Tachometers

Sharecropper

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I’m in the process of installing a new 6.5 engine in my M1028 CUCV truck, mated to a rebuilt 700R4 transmission. Because the 700R4 will not require vacuum to operate, I have installed a HMMWV oil pump drive in place of the vacuum pump on the rear of the engine valley. Because the oil pump drive also drives a tachometer in HMMWVs, I am considering installing a HMMWV tachometer in my truck.
Question - what are/were the different variations of tachometers used in HMMWVs over the years? I’m thinking I would want to use the version which was illuminated with a bulb instead of translucency.
Thanks in advance for comments.
 

BLK HMMWV

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The tach I have in my HMMWV is located up high near the windshield wiper motor.
It doesn't have a factory option for lighting it. It uses a 3 pin I believe cannon or military connector.
I read someplace that someone modified theirs to add a light .
A lot of people have used non HMMWV tachs that have a screw terminals on the back.
Those have a light built into them .
 

86humv

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I’m in the process of installing a new 6.5 engine in my M1028 CUCV truck, mated to a rebuilt 700R4 transmission. Because the 700R4 will not require vacuum to operate, I have installed a HMMWV oil pump drive in place of the vacuum pump on the rear of the engine valley. Because the oil pump drive also drives a tachometer in HMMWVs, I am considering installing a HMMWV tachometer in my truck.
Question - what are/were the different variations of tachometers used in HMMWVs over the years? I’m thinking I would want to use the version which was illuminated with a bulb instead of translucency.
Thanks in advance for comments.
There are 2 types...buss bar, and round threaded connector.
Only the buss bar type will work with that tach drive.
And tach is 0 to 3500.....not the 0 to 3000 ones out there, they wont work.
 

Sharecropper

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There are 2 types...buss bar, and round threaded connector.
Only the buss bar type will work with that tach drive.
And tach is 0 to 3500.....not the 0 to 3000 ones out there, they wont work.
Yes the 0 to 3500 buss bar type is what I am interested in. I saw one on Ebay recently but it had a translucent housing so light could enter the sides. Since my application will not have that type of lighting, I was curious to know if the earlier HMMWVs used a tach with a bulb socket.

Thanks.
 

86humv

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The hmmwv tachs all have steel case....and just the buss bar tach, has a light bulb and socket.
 

Andyrv6av8r

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Sharecropper

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Out of 3 tachs purchased, this is the only one that worked in mine. And it comes with a bulb.
It's been over two years since I purchased the brand new Tach and am just now getting around to installing it. Before I go to the effort to design and build a custom gauge panel for the tach, I wanted to test it with the sending unit to make sure everything worked. Well, I connected 24v and ground to the appropriate posts on the back of the tach, and then hooked up a redneck pigtail to the sending unit and wired that to the appropriate posts. I then chucked the drive post of the sending unit into my Milwaukee drill, and after making sure I had 24.2 volts to the tach, spun the driver up to 1700 rpm. The tach needle did not move at all. I replaced the quick connectors on the sending unit leads and then checked the circuits with my continuity tester, and everything checked out fine. I repeated the whole process a third time to make sure all connections were valid, but still not so much as a vibration on the tach needle.

What am I missing here? Is the tach body itself supposed to be grounded too? Thanks in advance for any comments.


IMG_4972.JPGIMG_4973.jpg
 

springer1981

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It's been over two years since I purchased the brand new Tach and am just now getting around to installing it. Before I go to the effort to design and build a custom gauge panel for the tach, I wanted to test it with the sending unit to make sure everything worked. Well, I connected 24v and ground to the appropriate posts on the back of the tach, and then hooked up a redneck pigtail to the sending unit and wired that to the appropriate posts. I then chucked the drive post of the sending unit into my Milwaukee drill, and after making sure I had 24.2 volts to the tach, spun the driver up to 1700 rpm. The tach needle did not move at all. I replaced the quick connectors on the sending unit leads and then checked the circuits with my continuity tester, and everything checked out fine. I repeated the whole process a third time to make sure all connections were valid, but still not so much as a vibration on the tach needle.

What am I missing here? Is the tach body itself supposed to be grounded too? Thanks in advance for any comments.


View attachment 861836View attachment 861837
You are not missing anything. I have the same tach and sending unit and it is hooked up the same way (basically) and it works great. I assume you have tried spinning it in both directions?
 

Sharecropper

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You are not missing anything. I have the same tach and sending unit and it is hooked up the same way (basically) and it works great. I assume you have tried spinning it in both directions?
Yes I spun it in both directions and also swapped the leads to the sender. Needle still dead. Do you think the tach case should be grounded also?
 

springer1981

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Yes I spun it in both directions and also swapped the leads to the sender. Needle still dead. Do you think the tach case should be grounded also?
You can ground the case since the light negative connects to the negative terminal and then also contacts the case. In other words, it won't hurt anything to try but I don't think that will make a difference.

Sent you a PM too.
 

Sharecropper

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You can ground the case since the light negative connects to the negative terminal and then also contacts the case. In other words, it won't hurt anything to try but I don't think that will make a difference.
OK I will be back at the shop later and will try it. Thanks for your help. Stay tuned.....
 

papakb

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Just curious, how you grounded your tach? Did you go from one of the tach mounting screws to the body or just jumpered it to the neg lead (black) coming up to the tach?
 

Sharecropper

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Just curious, how you grounded your tach? Did you go from one of the tach mounting screws to the body or just jumpered it to the neg lead (black) coming up to the tach?
I ran a separate wire from the negative buss on the firewall to the negative screw on the tach. Worked like a charm.
 

Mainsail

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Does anyone know the background on the tachs in the HMMWVs? Like, why? Is it to set RPM for the hydraulic winch using the hand throttle?

My Moto Guzzi that should have a tach doesn't, and my HMMWV that doesn't really need one has one from the factory. :unsure:
 
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