Distributor / tach drive on '72 small block

As with many Corvettes of this vintage, my tach stopped working many years ago. About 3 years ago I purchased from M A Motorworks the cross gear and coupling and had it installed by my mechanic.  It lasted about 162 miles. Tach stopped working.  I called M A Motorworks and they said that I should have also have installed a new distributor shaft and brass button. ( they didn't tell me that when I ordered the parts)  This past Sept. at Funfest in Effingham, I purchased the kit which includes the  cross gear & coupling, dist. shaft , and thrust washer. I also bought the brass button. My mechanic installed the parts this past week, and the tach worked for about 10 minutes.
Now he tells me that I need a new distributor.  How can that be??? Does any one have a suggestion or recommendation?  How about a HEI Dist? I would like to keep the original ignition shielding.

This a '72 350 200 hp Auto all original with 70,000 miles.

Dean

I would definitely check the cable...it causes more problems than the hardware in the dist. Seems like every time you remove and reinstall the cable for other repairs, it works for a while. Perhaps the end of the cable has rounded, and is no longer square enough to fit into the drive gear properly? A cable is a lot cheaper than a new dist...

It's also possible that the cable is loose on the back of the tach itself, but disconnecting the other end moves it enough to make contact for a while. I'd be checking both ends of the tach cable, before going another route.

Is this thing actually eating the dist gears, or is that just what is being replaced?Adams' Apple2007-10-22 18:49:12

I had the same problem, the cable was rounded off on the distributor end, making it work some of the time.

I agree that the cable end is probably rounded slightly.  As for switching to an HEI, you would need the later style ignition shield but it is worth the change over.  I did see an slight increase in HP and a big increase in fuel economy.  I bought the Summit HEI with Tach Drive.  It has an adjustable  vacuum advance canister. 

You will find that the best course with most of the work you do to these things is to start at one end and replace/repair everything along the line. The tach is no different. If you replace just one component in a string of components that make it work, you may be asing for trouble. If you are going to do it, do it all, do it right. Think about it, when you replace a clutch, you just don't replace the disk, you also do the pressure plate, through-out bearing, and pilot bushing. You car only has 70,000 miles, but it is 35 years old. MikeMc712007-10-23 06:00:03

Thank you all for a quick response to my tach/dist. problem.  I will check the cable to see if it is rounded.  Thanks again.

Dean

Again, thank you for your responses the problem with the tach/dist. in my '72 350.  To answer some of your questions, the cable end at the dist. is square and appears to be free wheeling. It also appears to be attached firmly to the tach gage in the dash.  Yes, to Adams' Apple, this thing is eating up the dist. gears.  The common thread among the responses, and other people I have talked to, is that it makes a lot of sense to upgrade to a HEI dist., therefore, I have ordered from M A Motorworks the HEI dist. with tach drive. I also understand that I need a new set of spark plug wires. (What's another $400.) The other question I have is will the '75-'77 top shield fit in my '72?

Thanks again for all your help.

Dean  

[QUOTE=blu72]I had the same problem, the cable was rounded off on the distributor end, making it work some of the time. [/QUOTE]

The shield will fit the car, but it may not clear the air cleaner...

The only other reason I could think of that would be chewing up the dist/tach gear repeatedly would be a lack of lubrication, if the cable is not bound up, and you said it seemed to spin freely...