Dead Tach
Thread Starter
Intermediate
Joined: Jul 2007
Posts: 28
Likes: 0
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
Justin
Burning Brakes
Joined: Jan 2007
Posts: 1,164
Likes: 1
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. 
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,114
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.
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.
Le Mans Master
Joined: Oct 2005
Posts: 6,247
Likes: 471
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.
7th Gear
Joined: Feb 2008
Posts: 7
Likes: 0
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.
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