Tachometer acting funny

[data89]

1st...my tach was running normal. I already had replaced most of the bulbs in the cluster with LED, but not the tach bulb yet. I had a problem with the gas gauge not registering and so took out the dash cluster and solved that problem.

While I had the cluster out I installed an LED bulb in the tach and bench tested it, so all the bulbs on the cluster and all gauges worked.

I put everything back together and started the truck ('69 Chevy C10 stepside) and there were tiny sparks showing in the tack when the lights were turned on. While revving the engine to check the tach they went away, BUT, now the tach will not go to zero either with the engine off or just idling. It stops at 2000 low end. It does indicate rpm's from 2000 to about 8000 whereas it used to go from 0 to about 6000 rpm.

What's going on with that???

[58 Special]

I had a tach once that the foam filter around it started to disintegrate.
Little bits of the foam were getting stuck in the tach causing it jump around when engine running and not going all the way to zero when engine off.

['68OrangeSunshine]

LED bulbs are diodes, so they have polarity. Incandescent bulbs don't. If your LED was put in backwards, it might have shorted out the tach.
''Little sparks'' are not a good sign.
What brand of tach was it?

[data89]

Originally Posted by '68OrangeSunshine

LED bulbs are diodes, so they have polarity. Incandescent bulbs don't. If your LED was put in backwards, it might have shorted out the tach.
''Little sparks'' are not a good sign.
What brand of tach was it?

This is an 1895 LED bulb and was bench tested in the cluster and worked. I'm thinking that if it was in wrong, then it would not have lit up. The other LED bulbs are 194's and they do have polarity to be observed or they won't light up.

I'll have to go look at the brand of tach...does it matter?

There must be a way to re-set this. It's a 4 hour job to take the cluster out again, and I'm replacing vent and window seals now.

['68OrangeSunshine]

Another question -- do you have any kind of Multiple Spark Discharge [MSD], Pertronix Ignitor III or the like?
Regular HEI and points are tach friendly. But the above type ignitions play hell with electronic tachs.

For a test, see if the tach works OK if you put the incandescent bulb back in?

[data89]

Originally Posted by '68OrangeSunshine

Another question -- do you have any kind of Multiple Spark Discharge [MSD], Pertronix Ignitor III or the like?
Regular HEI and points are tach friendly. But the above type ignitions play hell with electronic tachs.

For a test, see if the tach works OK if you put the incandescent bulb back in?

Just a standard original distributor with points. Was working fine before changing to LED. However to change bulbs I'm looking at 4-5 hours of taking the dash cluster out and apart to get at the tach. I'm going to do some testing and checking of the wires and it's been suggested I try a magnet to bring the needle back to 0.

['68OrangeSunshine]

I had a tach that was acting screwy. I was looking at replacement prices. My tach was an aftermarket AutoSun, and mounted on my steering column with a hose clamp. Anyway, I found one of the wires under the dash had been snatched by a parking brake spring and broken. After a resplice, it worked fine again.
With a built-in Factory tach, you probably won't find a gripe like that, but it could be something similar.
Hope you didn't fry your tach.
Good luck.

[data89]

Originally Posted by '68OrangeSunshine

I had a tach that was acting screwy. I was looking at replacement prices. My tach was an aftermarket AutoSun, and mounted on my steering column with a hose clamp. Anyway, I found one of the wires under the dash had been snatched by a parking brake spring and broken. After a resplice, it worked fine again.
With a built-in Factory tach, you probably won't find a gripe like that, but it could be something similar.
Hope you didn't fry your tach.
Good luck.

It still works, but now goes from 2000 to 8000 rpm when I increase speed instead of 0-6000 rpm.

['68OrangeSunshine]

Your tach needs recalibration. I think Board Member, ''T-Bone'' did that.
Maybe someone with more knowledge of tachometer repair will chime in...

[data89]

Originally Posted by '68OrangeSunshine

Your tach needs recalibration. I think Board Member, ''T-Bone'' did that.
Maybe someone with more knowledge of tachometer repair will chime in...

Hope so, otherwise I'll just have to live with it, or recalibrate my brain.