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Tach question

Green Monster

Green Monster

1/2 ton status
Joined
Aug 10, 2013
Posts
328
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Location
Thousand Oaks, CA
76 K5 with HEI. Tach never worked right. We're going through all the gauges, and can't get the tach to work right. It reads way too high, and when the truck is turned off, it doesn't return to zero. Looking at the LMC harness for this year with the HEI, it doesn't look like our harness. Would a points harness create these issues? Will the HEI harness fix it?
 
The wiring won't fix that problem. The needle should go to zero with key on, engine not running. If it doesn't, I would wonder if the needle has moved on the shaft. If it isn't that, I don't know how to change the calibration. I assume that it is a factory in dash tach?
 
6872xtc said:
The wiring won't fix that problem. The needle should go to zero with key on, engine not running. If it doesn't, I would wonder if the needle has moved on the shaft. If it isn't that, I don't know how to change the calibration. I assume that it is a factory in dash tach?
Click to expand...
Yes, factory tach. I'll check to see if it's possible that the needle has moved on the shaft.
 
Green Monster said:
76 K5 with HEI. Tach never worked right. We're going through all the gauges, and can't get the tach to work right. It reads way too high, and when the truck is turned off, it doesn't return to zero. Looking at the LMC harness for this year with the HEI, it doesn't look like our harness. Would a points harness create these issues? Will the HEI harness fix it?
Click to expand...

Somewhere I have a tach cluster for the early square body and was told when I got it that everything worked. Would be willing to sell it if you're interested.
 
It's relatively common for the tachs to fail and read incorrectly. I think you can google and find info on it, and ways to repair it. There is a specific piece (chip?) that fails IIRC.

I'd wager it's impossible for the needle to slip. Someone might screw it up, but if it slipped once, it'd slip again. Don't mess with the needle. If you do it wrong, you break the post and ruin the gauge, and those tachs are not cheap nor common.
 
dyeager535 said:
It's relatively common for the tachs to fail and read incorrectly. I think you can google and find info on it, and ways to repair it. There is a specific piece (chip?) that fails IIRC.

I'd wager it's impossible for the needle to slip. Someone might screw it up, but if it slipped once, it'd slip again. Don't mess with the needle. If you do it wrong, you break the post and ruin the gauge, and those tachs are not cheap nor common.
Click to expand...
We messed with it again and it looks like it's shot.
 
I have a local place that repaired a couple for me.
Precision radio in San Antonio Tx.
 
On the factory tack the needle will stay at whatever rpm the truck is shut off at. If you turn the key on to ignition with out atarting it it will return to 0
 
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