Good thread below regarding a tach that outright quit. My 71's tach usually works but sometimes bounces and then dies a few miles down the road. Is this also likely to be the drive gears or ???? Thanks, K
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Re: C3 Tach failure continued
Follow the good advice on the similar thread including the part about 'exercising' the tach using an electric drill to fault isolate between distributor drive and cable/speedo head sub-systems.
Also, look closely at the end of the cable that enters the dist drive. This has a squared off shape. If prior owners/mechanics got in a rush and failed to install the cable FULLY in the dist drive, it could show rounded corners--wear that can/does cause the 'funnies' you're seeing. This would be a cheap fix with a replacement tach cable or rebuilding the internals of your existing cable.
Last, make sure the distributor is 'clocked' properly. It's possible to R&R the distributor and come off factory spec by a tooth or two and compensate with timing adjust. In this case, the dist tach drive outlet will be mis-oriented and place excessive side loading on the tach cable. The #1 plug wire on the dist cap should be in approximately the 2:00 position (looking from the rear of the engine) with the dist vac advance nipple clearing the dist shielding support with comfortable timing adjust margin and the rear tach cable drive slightly off-center (7:00 position) pointing toward the driver side....
If the dist is NOT 'clocked' properly, make sure you re-clock it right during your fault isolation efforts. Good luck!
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