gauges

[hargray2]

The needles on the tach and speedo in my car
bounce around. The needle on the speedo bounces up and down while accelerating and then settles on the correct speed while cruising. The problem is in the speedo, cause I checked it with an electric drill directly
to the back of it. The tach does basically the same. It bounces past and below the actual engine speed, and then settles at the
correct rpm if you hold the pedal steady.
Does anyone know how to remedy this problem?
I took apart the tach doing cosmetic work
and noticed what appears to be an adjusting
screw with a locknut on it. This may tighten
the bouncy spring, but also may throw it out
of calibration. If anyone has dealt with this
before, please enlighten me!

[HMeeder]

Well, The two guages operate on very different principles. It may seem like they are doing the same thing, but that would be very unlikely.

The tach operates off a signal that comes off (I think this is right) the coil. Your problem may stem from a connection or grounding problem. Double check all wiring!

The speedo/odo may need to be pulled apart. That problem sounds mechanical and if you follow the tech article you should be able to revive it. Seems like it may just be that some lubrication and clean-up is in order.

Good luck!

------------------
Herb
'72 1.7 Tangerine 'Teen
'74 2.0 Red Rustmobile

[John Rogers]

Tach bounce is usually caused by circuit deterioration inside the tach due to old age and as far as I know a repair shop has to fix it. The best suggestion would be to have a shop do both the tach and speedo as they can calibrate them, etc. Good luck.

[Dave at Pelican Parts]

The tach is run off of the points. If you still have points, check them for pitting/contamination/etc., check the point gap, the dwell, and the timing.

It may not be the worst idea to just replace the points & condensor "just because", or at least as a troubleshooting measure.

Also check all of the wiring.

If that doesn't do anything to fix the tach, then the problem is inside the gauge itself. When you see what a rebuild costs, you may decide to live with it...


The speedo is a different matter. The connection is all mechanical. Often, the bouncing speedo needle is a sign of a speedo cable that is dying. (See the thread from just a few days ago for an example.) It is possible that the problem is inside the gauge, but it is unlikely.

--DD

[campbellcj]

My tach bounce, and subsequent total failure, was simply due to the crimp connector on the coil tach signal line working loose. It looked like it was attached, but the electrical connection was poor and intermittent. Check the coil wires!