KJLive

I live in PA. Needless to say, it is cold now! I never drive my Vette after October. However, I needed to drive it to take some photos for a magazine article. Anyway, my tachometer needle goes crazy when it is cold. This time, the needle actually snapped and broke. I assume it is a difficult job to remove the tach for a repair? any opinions or thoughts?

Gordonm

Its not easy as you have to remove the tach head from the dash. SO the right side dash panel needs to come out. The bouncing needle when cold is probably the tach cable grease being very old and binding up. The other issue may be the gears inside the distributor. All of this can cause bouncing. Even so you need to remove the tach and fix the needle. You can get replacement needles though. Not hard just time consuming. While it is apart clean the old cable or replace it and check the gears inside the distributor.

Should say left side dash panel.

KJLive

I appreciate the advice! Thank you. Any on line recommendation to walk me thru the process?

Gordonm

Yes. Google is your friend. Many videos and online instructions. Wilcox has a good step by step procedure.

0Willcox Corvette

Here is a step by step instruction sheet on how to remove the left hand dash pad. It is the easiest way to do this job and will also prevent the common issue of damage to the left pad if the column is left in place.

http://repairs.willcoxcorvette.com/w...ad-removal.pdf

The issue as Gordonm stated could be the cable, but it's probably in the speedometer/tach head and unlikely (but possible) the drive gears. Drive gear failure usually results in complete failure of the tach head. If the cable has had regular grease put on it the grease will work it's way into the first worm and magnet bushing. (the cable is reverse wound and that's a no no). When this happens it will eat out the first worm bushing over time. You can read the original delco lubrication sheet below.



About the only thing that can slam the speedometer/tach needle to where it would break off is if the first worm magnet has come in contact with the speed cup. Again this is caused by a first worm and magnet bushing failure which allows the first worm magnet to **** to the side. Normally a speedo/tach will start to show signs of this by making a tinging or a slight scraping noise and erratic behavior. Once this starts happening and once the magnet actually catches the speed cup and then needle and possibly the speed cup are destroyed. You'll know if the speed cup is destroyed when you remove the tachometer from the dash. if you look at the needle and part of the speed cup shaft is broken off inside the needle you'll know.

To help you understand what I'm talking about.. The only difference between the speedo and tach would be the second, third and fourth worm gears which drive the odometer.

KJLive

This is great information and very helpful! Thanks to both of you! I haven't experienced any issues with the tach not functioning unless it is very cold. Then I encounter the tinging or a slight scraping noise and erratic behavior you mentioned. During the warmer months it works fine. I never drive the car in the cold weather. Unfortunately I needed to get a few photos. I learned my lesson! Thanks again!!! I really appreciate all the help. Obviously, I need to get the tach out to assess whether or not it is still OK.