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> Bouncing tach and speedo, where to start
hndyhrr
post Apr 16 2026, 07:38 PM
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Last time i drove the pumpkin got almost home and had the fuel pump and master cylinder go side ways on me.

New MC is installed and brakes bled.
new fuel pump and gas tank going in this weekend.

During that drive I noticed that the tach and the speedo were bouncing alot. The speedo milage has never worked but the trip milage did.

Could this be a ground issue?

WCR is coming up and need to have it all taken care of.

Thanks guys

Renee
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barefoot
post Apr 17 2026, 06:42 AM
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Speedo is not electric, look for a twisted speedo cable back at the tranny.
My speedo angle drive on the tranny had got loose & rotated so the cable got kinked.
had to get new speedo drive gear sequently.
OR if you're just lucky just lube the cable from the speedo end. (IMG:style_emoticons/default/smile.gif)

Barefoot
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porschetub
post Apr 17 2026, 04:26 PM
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QUOTE(hndyhrr @ Apr 17 2026, 01:38 PM) *

Last time i drove the pumpkin got almost home and had the fuel pump and master cylinder go side ways on me.

New MC is installed and brakes bled.
new fuel pump and gas tank going in this weekend.

During that drive I noticed that the tach and the speedo were bouncing alot. The speedo milage has never worked but the trip milage did.

Could this be a ground issue?

WCR is coming up and need to have it all taken care of.

Thanks guys

Renee

A bouncing tacho can be wiring issue from the engine bay (coil ) to gauge ,bad earth etc or the gauge itself is failing and has lost its stability which means there is a fault in the 50yr old driverboard .
Speedo will be a bad cable or broken/misaligned drive cog/s ,cheers.
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jim_hoyland
post Apr 17 2026, 05:51 PM
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I remedied a bouncing speedo with a cable lubricant.
Disconnected the cable at the gauge and put the lubricant into the cable,
As I remember it took a fair amount and was difficult holding the cable in a suitable position; now, the gauge is super smooth above 15 mph


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Steve
post Apr 17 2026, 06:36 PM
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My bouncy tach was bad capacitors. I had North Hollywood Speedometer rebuild it.
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mjrrti
post Apr 18 2026, 11:05 PM
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QUOTE(hndyhrr @ Apr 16 2026, 06:38 PM) *

Last time i drove the pumpkin got almost home and had the fuel pump and master cylinder go side ways on me.

New MC is installed and brakes bled.
new fuel pump and gas tank going in this weekend.

During that drive I noticed that the tach and the speedo were bouncing alot. The speedo milage has never worked but the trip milage did.

Could this be a ground issue?

WCR is coming up and need to have it all taken care of.

Thanks guys

Renee


Take a look at AshLOCKTECH.com He sells a Tach adapter that cleans up the signal to your tach. It can also be used to make your tach work with all different numbers of cylinders and old and new ignition systems. I have not used one on a stock setup but I bought one to drive my tach on a Subaru conversion and it works great. Very smooth needle from idle to redline. You move dip switches for different configurations. It has been a while but I remember it being easy to hook up with good directions on how to do it for your setup. It has been working in my car now for around 10 years. I am very happy with mine. (IMG:style_emoticons/default/driving.gif)
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porschetub
post Apr 19 2026, 02:38 PM
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QUOTE(mjrrti @ Apr 19 2026, 05:05 PM) *

QUOTE(hndyhrr @ Apr 16 2026, 06:38 PM) *

Last time i drove the pumpkin got almost home and had the fuel pump and master cylinder go side ways on me.

New MC is installed and brakes bled.
new fuel pump and gas tank going in this weekend.

During that drive I noticed that the tach and the speedo were bouncing alot. The speedo milage has never worked but the trip milage did.

Could this be a ground issue?

WCR is coming up and need to have it all taken care of.

Thanks guys

Renee


Take a look at AshLOCKTECH.com He sells a Tach adapter that cleans up the signal to your tach. It can also be used to make your tach work with all different numbers of cylinders and old and new ignition systems. I have not used one on a stock setup but I bought one to drive my tach on a Subaru conversion and it works great. Very smooth needle from idle to redline. You move dip switches for different configurations. It has been a while but I remember it being easy to hook up with good directions on how to do it for your setup. It has been working in my car now for around 10 years. I am very happy with mine. (IMG:style_emoticons/default/driving.gif)

The tach-adapter will do everything you have mentioned ,however it will not "clean up the tach signal' ,it was never designed for that , he sells a modern replacement driverboard which is pretty easy to fit once the tacho is apart and comes will full instructions ,cheers.
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sholman5
post Apr 20 2026, 10:41 PM
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Clean the contacts on the rotor and distributor cap.
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