Inaccurate tach?

Daniel McCurdy

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So according to the gear calculator my tach is reading a few hundred rpm high. I have a zf5 close ratio. When I had the diff cover off it said 4.10 on the gear and I have a 33in tire
 

Austin86250

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these factory tachs aren't the most accurate things in the world
if your that concerned about you rpms get an aftermarket tachometer
 

TNBrett

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When I first got my truck, I was concerned that someone had swapped from 4.10’s to 4.56’s. The tach was off that much. I had bought a junk cluster off of eBay to replace the odometer screen that had turned black, and I put the parts tach module in by accident when putting things back together. Low and behold my RPM dropped significantly at cruising speed. The better tach is still about 100rpm higher than my timing meter at 2000rpm.
 

Daniel McCurdy

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Crazy how far off they are. I was thinking of trying to put in a real oil pressure and volt gauge where the factory ones go. Might as well try and do a tach as well.
 

Black dawg

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I have not done it with one of these, but on other vehicles I have pulled the needle off and repositioned it......might take a little trial and error.

Had a 6.5 truck that it was off a couple hundred rpm and drove me crazy. After I moved it, it read about 50 rpm low......
 

rvitko

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I did as Black Dawg said, I took my whole cluster apart as none of my gauges were working well and used CRC electronics cleaner and Penn reel oil in a little dropper and managed to get them all working and while it was a major PITA I was able to get the needles more accurately placed, Tach and Speedo are the worst though, on all of them the needle is on a little tiny pin and if you bend or break it, done, and you have to push gently. What makes Tach and Speedo so hard is Speedo is spring loaded and has a stop and depending on how you hold the gauge the needle will be at the stop, past the stop, it takes some finagling, the Tach is hard because with no current at all working on a dead cluster, its way off, my advice is to install it so it has power, energize it, turn it off and then set the needle at zero and try from there. I used a plastic trim puller with a really narrow V to pop them off and while I had them off, I gently rubbed the faded paint off and bought some needle paint, I will say though to do it right, you need needle yellow and needle white, you should put white behind the yellow, that is how it was from the factory, I only bought the yellow so they are sort of see through yellow. I put in new gauge face decals, while I get it isn't everyones taste, I like it, my truck is red and white and I wanted to tie in the red inside as my interior is grey, so I did this and red floor mats.
 

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