Problem with Tach Drive Distributor

[Steve V.]

Anyone else find or solve this problem??

[Michael G.]

Re: Problem with Tach Drive Distributor

Steve, Are you sure the small, hardened washer is in place between the tach drive gear and the coupling? Also check the nylon button in the housing for the tach drive. If OK, you should try to determine the contact point of the two gears. This binding should be leaving some telltale markings on the brass which will give you an idea of where the two are mating. An over-abundance of shims at the main driven gear, or scratches on the bottom of the breaker plate will indicate the main shaft is being drawn down into the housing too far. This too could affect the contact point of the tach drive gears. Good luck, Mike

[Steven G.]

Re: Problem with Tach Drive Distributor

The distributor must turn freely as I'm sure you know, even if it means shimming. You may try marking gear like setting up a ring gear and pinion to locate where/how the gears are mating to avoid future wear and damage. Steve

[Jim T.]

Re: Problem with Tach Drive Distributor

I don't know how many threads of the tack gear coupling you are screwing into the distributor, but it does not take a lot. Do you have the thrust washer on the tack gear? The distributor shaft also needs to be shimmed. You mentioned reading great articles on disturbutor rebuilding, did you read this one?

http://www.tispecialty.com/articles/article6.htm

[Ken A.]

Re: Problem with Tach Drive Distributor

Your problem could be with the new shaft. Reinstall the old shaft and see if the problem resolves itself. If so, you can reuse the old shaft by rebushing the lower shaft. In addition, the top bushing must be installed with a correct amount of bushing above the housing (.500 inch, I think). If too deep or too high, then the problem you describe occurs. Most top bushings do not need replacement.

[Steve V.]

Re: Problem with Tach Drive Distributor

Many thanks to all for the suggestions. I will try the gear marking grease today. The harden washer between the tach gear and coupling is in place and I have made a custom nylon insert to keep the tach gear shaft in close to original position and maintain about .010 axial end play. The upper bearing was replaced because the main shaft was riding too low which would have required over 0.150" shiming on main gear, so I pressed in the new upper bearing a little higher to raise the main shaft and reduce the shimming on the main drive gear. Main drive gear shims are currently at .055 to give .005 axial end play on main shaft. Do you think this small upward positioning of the shaft to cause this problem, or that current shimming is excessive? The article that provided the most help to me was the referenced Dave Fielder's restoration article.

I continue to think the issue is with the seating of the tach gear coupling since things rotate freely until the last 1/8 turn of the coupling. It seems the coupling moves to increase gear interference when seated. I tried teflon tape around threads of coupling to help hold it in center when tightened, this provided some reduction in friction but not sufficient.

Thanks again for the great ideas, I will continue to struggle with this till I get it right.

[Timothy B.]

Re: Problem with Tach Drive Distributor

Steve,

There is center to center mis-alignment between the two gears, it could be caused by the new bushings. I am told that it's necessary to ream the bushings in a jig to make sure everything is straight top to bottom and your new bushings may have moved the main shaft slightly off center..

Try to re-index the tach gear to the main shaft gear by walking it around to different positions as you may find a sweet spot where it turns freely when the brass coupler is snug. I had this same problem with a stock original distributor and that did the trick..

If the old gears don't correct the problem then the solution is to have the distributor bushings reamed. I can't remember who does this, that's why most people stay away from replacing distributor bushings.