71 Tachometer going bouncy-bouncy

[Norman S.]

What are fix instructions for this apparently typical problem? Tach works when cold for a while then stops.
What part(s) need replacing?
Thanks.
Norm

[Terry M.]

Re: 71 Tachometer going bouncy-bouncy

Norm,

You (because you have the car and we don't) will have to do some troubleshooting.

1) remove the tachometer drive fitting from the distributor -- it just unscrews and should be not much more than finger tight.

1A) Examine the end of the drive cable to be sure it is square and not chewed up. If it is chewed up you will have to replace the drive cable -- see your copy of the FSM (Factory Service Manual).

1B) remove the tachometer drive gear from the side fo the distributor. THere is a slot int he drive gear housing that will accept a large common screwdriver. Unscrew it and clean and examine the drive gear. If the teeth are chewed up you will have to replace BOTH the drive gear and the distributor main shaft. That job is a whole other post, so don't go there unless you need to.

2) if the above checks good visually the issue could be in the tachometer head. Remove per the FSM and send/take it to your favorite tach/speedo shop.

[Joe L.]

Re: 71 Tachometer going bouncy-bouncy

What are fix instructions for this apparently typical problem? Tach works when cold for a while then stops.
What part(s) need replacing?
Thanks.
Norm

Norm-----


Most likely, the problem is in the tachometer head but it's a good idea to check out the things that Terry mentioned first.

Corvette mechanical tachometers are not a direct drive type of unit such as those once used in race cars. The mechanism is "dampened" and as the mechanism gets old and worn, the "dampening" deteriorates. Then, you get a "bouncy" needle.

[Norman S.]

Re: 71 Tachometer going bouncy-bouncy

Thanks to you and Terry for your valued help.