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General Category => The Interceptor Gang => Topic started by: thomy on February 05, 2014, 02:07:05 PM

Title: Bouncing Tach
Post by: thomy on February 05, 2014, 02:07:05 PM

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

Title: Re: Bouncing Tach
Post by: gixxer6 on February 05, 2014, 02:33:03 PM

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. 

Title: Re: Bouncing Tach
Post by: thomy on February 05, 2014, 03:03:57 PM

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.

Title: Re: Bouncing Tach
Post by: Dandb7 on February 05, 2014, 03:58:35 PM

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

Plenty of those for sale on the Internet !

It's snowing...  :)

Title: Re: Bouncing Tach
Post by: thomy on February 05, 2014, 06:48:59 PM

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.

Title: Re: Bouncing Tach
Post by: mswyka on February 05, 2014, 07:09:46 PM

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. 

Title: Re: Bouncing Tach
Post by: sprocket on February 15, 2014, 09:30:54 PM

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

Title: Re: Bouncing Tach
Post by: thomy on February 19, 2014, 12:41:48 PM

What does the resistor do in this case?

Title: Re: Bouncing Tach
Post by: kawhead on February 20, 2014, 08:16:22 AM

my guess is to even out voltage spikes.

Title: Re: Bouncing Tach
Post by: thomy on February 20, 2014, 01:31:43 PM

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.