Hank

Hi everyone,

on my 66 roadster the tach has stopped working. I checked the cable and spinning with a drill (counterclockwise) the gauge in the dash does spin... so i'm thinking it's the distributor end.

I have an MSD 8572 distributor with a tach drive built into it. Is there a way for the distributor end cable drive to break?

How to I test that or what repair parts do I buy?

I looked on the MSD website and only found guidance to the little brass connector they sell... I already have one of those connectors, and (a) the tach used to work, with this distributor and no connector, and (b) I can't make the connector fit into the tach drive anyway.


Thanks,
Gerry

landshark 454

Inspect the tach gear in the distributor. This is what always went bad in the factory distributors.

wmf62

mechanical tachs usually don't fail suddenly, they start to bounce before quitting

is the dist end of your tach cable square? is it still square? does the dist tach drive shaft have a square hole in the end? is the hole still square?

start the engine, with the tach cable disconnected from the dist and feel to see if the tach drive shaft is turning. if it's not, then the gear inside the dist is stripped. it is possible that it will turn without the tach cable being inserted as there is no load from the tach/cable.

it would be nice to have something square of the size and length on the inserted length on the cable end to stick into the end of the dist shaft and try to turn. you can make something by getting a nail of the right diameter and filing it square. bend it L-shaped and stick it into the shaft end to various depths and try to turn it; this will tell you if the hole is square to the right depth or whether the shaft gear is stripped.

if, as you have said, the tach works when you spin it with a drill and the dist end of the cable is good, then the problem is with the dist tach drive.
Bill

Hank

Closing the loop here on what happened, in case it helps some future desperate corvette owner:

1. I removed the distr from engine. when spinning the distr drive gear that rides on the cam, the tach drive spun too, so distr tach drive internal gear is not the problem. And we know the tach itself is not the problem. So... the cable is not engaging with the tach.

2. I tried fitting the MSD brass part again, between the cable and the distr. MSD brass part fit into the distr and appeared to "hook" well but now the cable itself was 3/8" too long and the cable housing would not seat against the tach, nor would the threaded cap that holds cable to tach engage.

3. Cringing, and with bubba forever tattooed on my forehead, I cut 3/8" off the square tach cable end and fitted the brass MSD part over the amputated cable.

4. Reassembled things

5. The tach now works fine.

What is REALLY ODD about all this is that for 9 years this distributor and this tach cable lived together in harmony and worked. Then, one day, they didn't. And adding this new MSD part, including required chop chop to the cable, then got them to work again. That goes down in my book as "it works in practice but not in theory".

Getting stumped is half the fun...

Gerry