Bouncing Tach

[thomy]

I took the Interceptor to the track last Sunday to see what bugs I had to work out of it. There are a few.

A couple of days before this I had taken the tach off because it was spinning in the thin aluminum dash I had made. I knew that I'd hooked it up wrong when it didn't work at all after I put it back in the dash. So I changed the red wire back to where it was originally and the tach worked. One thing I noticed that I hadn't seen before was that sometimes the tach needle would suddenly bounce around and shoot up to nine grand then go back to idle rpm again. Could this be due to a bad voltage regulator or is it just a bad tach?

Is this the same tach as the Invaders and LTDs?

Thom

[gixxer6]

Bouncy Tach's are quite common.  I think something wears out inside them.  I have some that did it really bad, some that do it just a little, and installed NOS ones that don't bounce at all. 

I'm not sure if the Interceptor tach has the same p/n as the Invaders, but I know they will work. 

[thomy]

Thanks. It worked without bouncing before I hooked it up wrong. I'll try another tach.

Not knowing exactly how these tachs work I still wonder if a voltage spike from a dysfunctional voltage regulator could affect the tach or even damage it.

[Dandb7]

Interceptor and Invader tachs are the same part number...

Plenty of those for sale on the Internet !

It's snowing... 

[thomy]

Wish it would snow here too. We lost ALL of our snow over a week ago to the pineapple express. The lakes are frozen good again and the oval track is beautiful but the only snow is in the snow berms of the ice roads and driveways.

Good thing I've got a couple of Invader tachs to try. Glad to know they're the same part numbers.

[mswyka]

the tachometers just convert pulses to an analog scale.  changes in voltage should not affect the units.  like all these old parts, they can only function so long before they quit. 

[sprocket]

You need to buy a inline gold resistor from Wahl brothers or wahlracing.com you want to add this including your stock one. This helped me on my tach issue, what I also found out on the dyno that my new factory tach was reading off

[thomy]

What does the resistor do in this case?

[kawhead]

my guess is to even out voltage spikes.

[thomy]

If there are any voltage spikes then the voltage regulator isn't working properly. If I understand correctly the resistor reduces the voltage by a certain percentage based on the resistance of the resistor.