Jumping Speedometer C3 1977

[jim34671]

What would be associated with a jumping speedometer needle.
Bounces until steady state speed reached..then OK
It even does so over bumps.
Drive cables?..Speedo unit itself??

[Steve Junkersfeld]

Re: Jumping Speedometer C3 1977

Jim, You didn't indicate if your car has cruise - but my 77 speedometer acted up prior to my cruise transducer going bad. The cruise transducer interupts the cable between the transmission and the speedometer. In the absence of a cruise control, I'd suspect a dragging speedo cable. Good Luck Steve

[jim34671]

Re: Jumping Speedometer C3 1977

Yes,It's got cruise control but inoperative.
Both upper/lower cables in place.
Jim

[Steve Junkersfeld]

Re: Jumping Speedometer C3 1977

Jim, There are a couple of metal disks in the transducer that transfer the rotation of the cables. My speedometer problems went away when I replaced the transducer. The transducers run $65 - $85 rebuilt. Steve

[Rich Beauchamp]

Re: Jumping Speedometer C3 1977

For what it's worth, my 82, 24,000 miles, had a similar problem. The cruise control transducer was going bad. Cleaned it up, and it ran about 100 miles, then failed again. Replaced it with a rebuilt one from Volunteer Vette, and it works fine. Also had to replace the little gears in the tranny. Well... actually, the mechanic did all the work, I just paid for it! The transducer was about $85.00, then a couple of cables as well.

Hope this helps!