Usafstingray

I need a little help with the tach drive gear assembly. I just rebuilt the distributor and used the brass button in the backside of the tach drive hole with the shaft of the button in the hole in the back...seems to make sense, but the tach drive gear housing doesn't bottom out the way it should when you screw it all the way in. The gear won't spin freely. Is this brass button correct? I've also seen a plastic one in the Long Island catalogue. This is a '65 L76 original distributor.

tbarb

Your problem is that the brass button should be set flush into the housing, tap it out and have a machine shop face the area down approx the thickness of the bushing (.065+-).

You can also use it like it is but the thrust washer that goes between the gear and screw in bushing needs to be removed. This washer is there to protect the screw in bushing as the thrust is inward when turning.

I would have the area faced and use the washer where it's supposed to go. Cut the new bushing stem about 1/8" short of the outside housing, tap it in and finish the outside with some J&B weld. After hard, get a sharp razor and slowly scrap the excess off and paint. Looks like it was never touched and a excellent repair.

One tip, you can use the screw in bushing as a guide to center the hole for the new brass bushing. Sometimes it's hard to start the drill because the tach gear wears so nicely into the housing it almost looks like it's supposed to be there and it leaves a little tit in the middle.

redvetracr

the bronze button is too thick it moves everything out as does the aftermarket plastic button, a factory button as used in the early 70`s will probably work, if you can find one...OR send it out to CF member Lars and have him fix the housing correctly.

Usafstingray

Is it an option to just go without the brass button? If the thrust is into the cable, it seems to reason that there wont be much wear on the back side of the housing...or does that allow too much play in the gear?

tbarb

The thrust is inward in to the distributor housing that's why the gear rides into the housing. Consider installing the brass button like I mentioned above before you get into $$ for a new set or gears because misalignment will damage them.

This repair can be done at home it's easy to do, get a drill bit the size of the screw in bushing hole and use the screw in bushing as a guide to start the hole and knock the little tit that forms when the gear indents into the housing. Then remove the screw in bushing and change the drill bit to the size for the new repair brass button stem and drill through the housing. Keep it snug so it's a friction fit and either have someone face the surface down an additional 1/16" so the new button sits flush inside the distributor housing or you need to remove the thrust washer that is used on the tach gear.

I suggest having the housing milled so you can use the thrust washer as it protects the screw in bushing from the tach gear.

Usafstingray

Well, the back of the housing already has a hole all the way through it, with a friction fit, as you describe, to hold the stem of the brass button. However, the back surface of the housing has not been milled down. Thanks for the help on this...I'll take it to my favorite machine shop and have it done there.

tbarb

Just to be clear, it's the inside of the distributor housing that needs to be milled so the button sits flat/flush with the surrounding surface. This way you can use the original tach gear and thrush washer with the screw in bushing.

lars

You should seriously reconsider using the brass button: The brass is not hard enough to provide a durable thrust surface, and your crossgear will eat itself into that brass button very quickly. The metal shavings from the brass button will drop down through your lower shaft bushing, and will destroy your bushing and mainshaft. I've seen it a hundred times. Either get the right nylon thrust button, or install a steel insert as a thrust surface. Don't mill the housing down to fit the junk brass button.

Lars

MikeM

One guy told me he silver soldered a hardened steel ball bearing on the end of the set screw to stop the wear. Period!

Usafstingray

Thanks for that sound advice Lars. Interesting that nylon would be the original material. What is the correct way to lubricate the gear and distributor shaft when putting it all back together? Do you grease the shaft and the tach gear? Do the holes in the distributor housing (shaft portion) provide oil up to the top shaft bushing?

tbarb

I can't argue your point, it may be easier and faster to drill through the housing and press a steel insert flush to the inside and be done.

I did mine years ago using the brass button and never had a problem. and have never heard of anyone having problems using the brass.

Do you have any pics of the damage using a brass insert?

JohnZ

Pack the tach drive cavity with lubricant before you install the cross-gear and coupler - that's the ONLY lubrication those two sets of gear teeth are ever going to get; only the bottom bushing sees engine oil. Dave Fiedler also has an article on tach drive distributor rebuilding on his site, www.tispecialty.com.

Usafstingray

Thanks everyone for the advice. It's done...rebuilt with nylon button and didn't drill the housing. With a new thrust washer and a new gear, it had .007 inch play. Its spinning now like my head was after three rounds of good scotch!