OMG! I'm looking for some tach knowledge

[bilfman]

Hey crew,

I am a stubborn old wrencher and usually beat my head senseless working through truck problems, usually the fix comes My recently redone 79 dually had many electrical gremlins to work through, gauges, lights, wipers, washer heater, got them all figured out. PITA stuff. Anyhow, now that the 'sex machine' is on the road it appears that the factory tach is out quite a bit, I would assume about 1000 rpm.

I have total faith in this site and only found it a few months back, I am now addicted and enter daily. I figured that I would just tap this wealth of knowledge for a starting point. So here is my question. Has anyone had experience with the factory tach? Is there any way to recalibrate or adjust it? I'm going to pull a spare aftermarket one that I have and just 'lay on the seat mount' to see how much the factory one is out, then take it from there.

My buddy and I tried the drinking a case of beer and staring at it last night, didn't work......now on to plan B

Thanx peeps!

[Weasel Diesel]

sounds like the stepper motor is about gone. Double check it with a hand held tachometer. If it is wrong, It can be repaired by a place that does cluster work, or find a replacement.

[joe231]

My factory tach was acting similarly.

What year is the tach?

If it has a sealed resistor pack on the back I don't know how to fix it...
If it has a circuit board with a multi pin black and white "chip" on it it is fixable by replacing part of the chip with a small resistor. It is a very small and tedious repair. If you have ever done circuit board lever repairs before you will know what I'm talking about....

Read this:
http://howtoalmanac.com/kevin/projec...chfixtruck.htm
Posted via Mobile Device

[bilfman]

Thanx guys, I at least have a good starting point. It is the stock 1979 tach and I would think it is reading about 1000rpm higher the the actual.

[TJBrown]

I sent mine to Wilcox Corvette and they rebuilt mine. They checked it before sending it back also. Think my bill was about $60. Think works like a champ.

[hatzie]

Originally Posted by Weasel Diesel

sounds like the stepper motor is about gone. Double check it with a hand held tachometer. If it is wrong, It can be repaired by a place that does cluster work, or find a replacement.

GM didn't start using stepper gauges before the T400 CK trucks.
The 73-87 squares are all air core meter movements. I believe 88-91 RV were still air core.

[Telecasterjoey]

Hey, I just repaired my factory tach using the info in this post. It was surprisingly easy I just added a variable resistor and it works perfect now. I just ran an autometer tach inline with the factory one and tuned the factory tach to match. I think this mod should be in the FAQ section it was very helpful

Link to the thread:
http://67-72chevytrucks.com/vboard/s...d.php?t=503733

Here's the site that shows you how:
http://www.howtoalmanac.com/kevin/pr...ve/tachfix.htm

[joe231]

Originally Posted by Telecasterjoey

Hey, I just repaired my factory tach using the info in this post. It was surprisingly easy I just added a variable resistor and it works perfect now. I just ran an autometer tach inline with the factory one and tuned the factory tach to match. I think this mod should be in the FAQ section it was very helpful

Link to the thread:
http://67-72chevytrucks.com/vboard/s...d.php?t=503733

Here's the site that shows you how:
http://www.howtoalmanac.com/kevin/pr...ve/tachfix.htm

the link I posted is for the truck tach specifically...
I didn't find it until yesterday.
I actually found a camaro message board with the how to when I did mine, same basic info...

[bilfman]

You guys are awesome! Hopefully I'll be spinning properly soon.-

[bilfman]

Originally Posted by joe231

My factory tach was acting similarly.

What year is the tach?

If it has a sealed resistor pack on the back I don't know how to fix it...
If it has a circuit board with a multi pin black and white "chip" on it it is fixable by replacing part of the chip with a small resistor. It is a very small and tedious repair. If you have ever done circuit board lever repairs before you will know what I'm talking about....

Read this:
http://howtoalmanac.com/kevin/projec...chfixtruck.htm
Posted via Mobile Device

Thanx so much for the link, got the part for $2.55, little solder action and I'm spinning properly. Love this site!!!