Mechanical Tach Question

[racingundertaker]

I am trying to get my mechanical tach to work again. My 73 Vette has a Mallory Distributor w/Tach Drive. I disconnected the tach cable at the distributor and turned the plastic end piece of the cable by hand. When I do this, the tach needle moves....so.....I am assuming the cable itself is ok. What should I look for next? When I disconnected the cable at the tach, I noticed that the plastic end piece just goes into the hole. Am I maybe missiing a piece, because it looks like the plastic end piece is square shaped and should "seat" into another square shaped piece in the distributor.....otherwise it would just spin around. Any help that anyone could give me would be greatly appreciated. Thanks......this forum is great!

 

[Alan76]

Tach Drive

I had the same problem on my 1973 convertible, mine has a stock distributor
so all I did was change the tach drive assembly. They have have a kit in
$70.00 to $80.00 range. Yours being a Mallory I don"t know if the stock replacement will work. Call Volunteer Vette in Knoxville Tenn and ask they
are good with getting you the right parts call 1-865-521-9100

Alan

 

[racingundertaker]

Thanks Alan........I will give them a call and see what they suggest. Is this a very difficult job? Can the kit be installed w/o removing the distributor?
Thanks again!
Mike

 

[Jack]

Disconnect cable at dist ... run the motor ... look closely into tach hole in dist ... you should see some clockwise rotation when motor running. If not, something's broken or missing in dist.

Conversely, lightly chuck the tach cable into a REVERSIBLE drill motor ... spin drill in reverse ... if drill runs at 600 rpm then the tach should read 1200 rpm. Cam, Distributor, Tach Drive and Cable operate at half-speed of engine (crankshaft) rpm.
JACK:gap

 

[racingundertaker]

Thanks for the suggestion Jack. I will try your diagnosis and report back with the results. Thanks!