Tach Problem

[Larry B.]

The tach on my '61 FI is reading low. When at idle it shows 500 RPM when it actually is 1000 RPM. At 3000 RPM it should be 4000 RPM. Any idea's or anyone had this problem. I don't want to tear the dash out if I don't have to!
The problem has been going on for a year or so and I am finally getting caught up to deal with it. I know aside from the tach it could be the cable or dist cross shaft gear, but not sure how to go about it. Thanks

[Terry B.]

Re: Tach Problem

Have you tried removing the cable and lubricating it and the connection point into the meter itself? There is an old article that you can search for that describes making a lubricant mix from penetrating oil and vaseline. My tach was fluctuating and I tried the described lubricant and it solved my problem.

[Larry B.]

Re: Tach Problem

Terry,

I know the cable was lubed a couple years ago with vaseline. There is no actual fluctuation. The tach stays constant all the time, it is just reading low.

[Jack H.]

Re: Tach Problem

Sorry to disappoint you, but the input drive is turning at a given rate based on the FI distributor rotation. So, for the tach to display a different/lower speed, it's NOT a drive cable binding/slip problem... Non-FI cars whose tach is fed from the generator CAN exhibit this kind of mis-match IF Bubba has installed the wrong drive pulley. But, you say the car is FI and I'm assuming the setup is stock.

That means the 'fix' is to pull the tach and send it out to a shop that's equipped to adjust the internal air gap and re-calibrate the magnetic drive/follower. Our United Delco shop here in Denver has the Delco calibration equipment certified for these tasks and it's roughly a $60 bench job.

[Larry B.]

Re: Tach Problem

Jack,

I believe the tach currently in the car was a non FI tach with the cable originally fed by the generator. The tach is now fed by the dist gear for the FI. Would that mean that the tach is not calibrated for the FI driven gear? If so, is the fix as you described? Regards, Larry

[Larry B.]

Re: Tach Problem

Anyone here on the forum able to fix this if I pull the tach out of the dash? Thanks

[John H.]

Re: Tach Problem

Anyone here on the forum able to fix this if I pull the tach out of the dash? Thanks

D&M Restoration in South Carolina can take care of it.

www.dandmrestoration.com