Dead Tach

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Feb 1, 2008 | 03:15 PM

justinw2116

Thread Starter

Intermediate

Joined: Jul 2007

Posts: 28

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From: Langley AFB VA

Dead Tach

When I bought my '74 the tach was jumpy. Then the ignition died. Then I had the ignition replaced the tach line was fine. Is there any rebuild kit of fixes that you would recommend a rookie looking into to restoring function to my tach.

Justin

Feb 1, 2008 | 03:37 PM

Glass Act

Melting Slicks

Joined: Jul 2005

Posts: 2,545

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From: 406ci SB, AFR 180 Heads - 490 HP @5,600 RPM 529 lb-ft @ 4,100 RPM

Sound like you need a new tach circuit board. You can buy them from almost any Corvette vendor or e-bay, for about $50.00

Feb 1, 2008 | 04:37 PM

7T1vette

Team Owner

Joined: Jan 2006

Posts: 37,637

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From: Crossville TN

HEI distributors didn't come out until '75...that's when I thought electronic tachs were installed in C3's. Is your distributor HEI or regular mechanical with the cable connection?

Feb 1, 2008 | 04:47 PM

Jeffery73

Burning Brakes

Joined: Jan 2007

Posts: 1,164

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From: Port Clinton Ohio

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

I believe a '74 runs off a tach drive cable from the distributor. I have the same problem on my '73 right now. The last time I drove it last fall, the tach started jumping around. Then it quit. The car was running fine, but the tach showed 0 rpm. I haven't had time to look into it yet. Been too busy rebuilding trailing arms, front suspension and replacing a radiator.

Feb 1, 2008 | 05:06 PM

7T1vette

Team Owner

Joined: Jan 2006

Posts: 37,637

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From: Crossville TN

With a mechanical [cable] drive distributor, there are three possible causes for your problem: the bevel gear set in the distributor has failed and needs to be replaced {remove tach, disassemble gear set, clean-up and replace gears, reinstall}; the cable has failed {most likely possibility....buy new cable & install per instructions}; the tach head has malfunctioned {least likely}.

Unscrew the coupling on the cable at the distributor. Then pull on the cable [firmly but not a hard pull] to see if a broken cable comes out. If so, buy a new cable and replace it. If not, leave the cable loose, start the car and see if the cable drive is turning on the distributor. If it is not turning, it's the gear set in the dizzy. If both of those things are working OK, it is likely a tach head problem.

Feb 1, 2008 | 06:46 PM

Jeffery73

Burning Brakes

Joined: Jan 2007

Posts: 1,164

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From: Port Clinton Ohio

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

Thanks for the info. I'll take a look this weekend..

Feb 2, 2008 | 11:22 AM

C3 4ME

Le Mans Master

Joined: Oct 2005

Posts: 6,247

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From: Glen Allen, VA

Don't know if there's enough give to do this with a tach cable, but with a speedo cable, I always chuck it up in a drill (in this case on the dist. end) and see if the tach works ok by the drill. If it does, then the dist. is at fault, if not the problem is somewhere else.

Feb 3, 2008 | 12:20 AM

rumblefish

7th Gear

Joined: Feb 2008

Posts: 7

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From: Diamond Springs Ca

tach fix??

I had a problem with erratic tach operation, I ended up inserting a small spacer ( a piece of a match stick) inside the distributor to prevent the tach drive inside the tach cable from working out of the tachometer head, its like the drive cable was too short. It has continued to work for about 30 years since.