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Tach gear drive replace


K Leitzel

Hello all. I recently replaced the tach drive gear side cross (purchased from Corvette Central) in my 1972 stock 350 engine distributor. I found this to be a very simple process to complete. When I started the car, I heard a loud buzzing sound at the tach drive gear area of the distributor and the tach needle in the dash was bouncing.
I unscrewed the coupler unit and realized that I forgot to install the tach drive gear bronze button first !! Had a heck of a time installing this button! Looks like the pointed end of the button goes in first, but the dang thing flipped around backwards and the pointed end was facing out at me! Then I couldn't remove the button! @#((#@((#$& Finally used my wife's tweezers (shhhhhhh) to remove the button. Anyhow, I reassembled everything (minus the bronze button) and now I'm back to where I started. Loud buzzing sound and the tach needle is bouncing?? HELP! Any suggestions?
Main Shaft?

Have you checked the gear teeth on the distributor mainshaft (mate to the cross gear)? They're hard to see without a good strong light and they may be gooped up with grease. Often, they're toast too! Hope this helps; let us know.
still buzzing?

Also, pull the coupler and gear back out again...leave them out...then run the car and see if it still buzzes. Also, when you reassemble, you'll probably need that button for proper gear alignment. If either gear is bad it will soon destroy it's mate. Check your new gear to see if it's been damaged / flat-spotted.
No buzzing?

If, after you've pulled the coupler and cross gear, and the buzzing stops with motor running...then try this too. With engine off, gently chuck the distributor end of tach cable in a reversible drill motor. Remember, facing the cable end, the cable turns CCW. You'll need long arms / a helper to do this and read the tach. Spin it up with the drill and see if the tach is bouncing or there's further buzzing. This helps pinpoint where the problem may be...there could be more than a single failure.

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