Help, my tach needle has gone nuts!

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Jan 29, 2010 | 06:16 AM

C3smallblock

Thread Starter

Racer

Joined: Dec 2009

Posts: 382

Likes: 8

From: Wellington

Help, my tach needle has gone nuts!

Just tonight my tach needle has started flicking down rapidly then correcting itself before flicking down again. It has pretty much gone mental! Any ideas on where to look for the problem? I guess it is a problem in the tach mechanism which means pulling half the car apart, but if there is anything easier to check first I would appreciate any advice.

Cheers
Kev

Jan 29, 2010 | 09:31 AM

Easy Mike

Team Owner

Joined: Jun 2000

Posts: 38,923

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From: Southbound

Cruise-In II Veteran

Probably a bad tach board.

Jan 29, 2010 | 02:59 PM

C3smallblock

Thread Starter

Racer

Joined: Dec 2009

Posts: 382

Likes: 8

From: Wellington

Where is that located? I am guessing on the back of the gauge?

Kev

Jan 29, 2010 | 07:32 PM

70ZZ3 96LT4

Burning Brakes

Joined: Oct 2001

Posts: 911

Likes: 5

From: TN

tack board

yep, 75 was the first year for the electronic tack. Another component is the filter for the electronic tack.

Jan 29, 2010 | 07:49 PM

Golden

Pro

Joined: May 2003

Posts: 593

Likes: 0

From: London England

You might want to check the top of the coil and the coil lead.

An ignition short across the top of the coil can cause electronic rev counters to go mad

Jan 30, 2010 | 12:02 AM

C3smallblock

Thread Starter

Racer

Joined: Dec 2009

Posts: 382

Likes: 8

From: Wellington

Well the plot thickens!

I just went to take the car out today and the main drive belt was screaming a bit (and the needle was still freaking out). So I shifted the alternator to take up the slack on the belt and now the tach is working fine again???

Coincidence or related?

I also hit a bump and bottomed out today and cracked my manafold in half, but that is another issue

Kev

Jan 30, 2010 | 03:36 PM

0Willcox Corvette

Former Vendor

Joined: Aug 2006

Posts: 76,656

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From: Jeffersonville Indiana 812-288-7103

St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15

Check the tach filter! It is common for the wire to break or come loose at this filter. Your bump may have jarred it enough to make good contact. If this is the problem sometimes a drop of solder in the end will be enough to make good contact again. It is pictured below and shown in gray.

If this is the problem and solder won't work, we have them in stock. http://willcoxcorvette.com/advanced_...=tach%20filter

Willcox