vette70

Haven't had a chance to look under dash or hood, but in dash mechanical tach up and quit.

What should I look for or where should I start looking. Was working when last drove as speedo is way off so I have been using tach as guage. Started up last night and no tach. Any ideas.

Vette70

the_lane

I have the same problem.

There are 2 faults that seem very common

tach Filter - this is a wire that filters out some current or something. It is in the engine bay. It can be bypassed to check too see if it is faulty

Tach printed circuit - circuit board on the back of the tach

vette70

Where would this wire be, I don't remember any spare wire in the area of the tach cable.

Gordonm

If your Vette is a 70 as in your signature you have a mechanical tach. No filter on it just a cable from the dist to the tach. Most common problem is the gear in the dist. Remove the cable from the dist and have some one else in the car. Spin the cable and see ifthe tach moves. If it does it is the dist gear. Dist removal is needed and a new gear and dist shaft is going to be needed. Not a big job but the parts are probably goingto be around 100 bucks.

vette70

Thanks Gordon I'll check that tonight.

Mike Mercury

and you also have the option of converting your tach over to electronic operation, and wash your hands of the mechanical tachometer aspects of that era. From the dash view, it still looks 100% original.

Fubba

Aren't you the one that converts them? If so, how much is it to do that?

Mike Mercury

please email me if interested:

tim-yvonne@juno.com

kdf1986

If you can spin the tach cable and the tach moves, then the problem is in your distributor like Gordonm said.

If its in the distributor, then either the cross drive gear is bad, or the main distributor shaft gear is bad....or both.

I had this same problem and the main distributor drive gear was bad which probably led to the failure of the cross gear. If you pull the distributor out you can then dismantle it to look at the main drive gear.

The tach drive cross gear will come out with out removing the distributor if you choose to do that first. It is held in place with a large slotted bushing.

kdf

Gordonm

Usually when the cross gear goes it takes the shaft with it. The usual cause for failure is the lack of any lube on the gears. If it is setup properly and lubed it will provide many miles of trouble free operation.

vette70

I checked the cable and twisted it around and indeed the tach needle moved.

If this gear is bad in the distributor would it also keep the vacum advance from working. The vette is running bad rough idil, wants to pop if you give it gas fast.

Are the two connected.

GTR1999

When the tach gears go they usually strip out the main shaft but the distributor will still function. The vacuum can has an arm that slips into the breaker plate and advances the timing when vacuum is applied. I would remove the distributor and take it apart for a good look at it.
Be aware some of the aftermarket main shafts and cross gears aren't all that good. The best source I found for them is Hi-Tech in FL, they make their own. Once you get the gears out and the housing clean,look in the bore for the cross gear to see if it's chewed up,also check the lower bushing for play.
Gary