usmilret

My speedometer is registering 30 miles an hour too fast. Even if I changed the original rear end gearing to a 355 gear the speedometer shouldn't be this fast. The speedometer is a 42 tooth (green) and I should change that to a slower speedometer gear. Problem is there are not too many options left to do so. So why is my speedometer registering 85 MPH when I am doing 54 MPH. Can the transducer have anything to do with it? This is indeed a head scratcher.

gdm78vette

Do you maybe have a metric speedometer and your reading is 85 kilometers per hour? That would be about 54 MPH.

mikem350

OK, assuming the speedo is not METRIC, when did problem start? What is history of your mods?

usmilret

Only one mod and thats changing the gears to a lower 3.55 gear ratio. No other mods. The original rear ratio was very high, something like a 2.11 or abouts. Before I changed the gear ratio the transmission shifted very late from first to second gear. Speedometer is U.S. However anything is possible.

terry82

2.87 aluminum wheel 2.72 standard wheels. I would call a tranny shop and ask them what color trans gear do I need with the new rear end gear.

usmilret

The Transmisison gear is green, a 42 tooth I believe.

usmilret

I called TCI and they were very helpful. They recommended a 15 tooth driven gear and a 40 tooth driver gear. That should do the job.

Grumpy 427

I went from a 3.08 rear gear to a 3.55 and all i had to do was replace the driven gear to the grey 22 tooth. Speedo is bang on now with a 295/50/15 rear tire.

AttyVette

Ok I know nothing about repairing speedometers so I thought I would ask here on this thread—does anyone on this site know of a good repair shop in Jefferson County Texas area, that can work on an 82 Corvette speedometer? When driving my 82’ Vette, the speedometer needle would frequently bounce around before it settled down while I was driving the car. Now, however, the last time I drove it (after taking it to a car show), it won’t register any speed at all. I am guessing that the cable broke but I am not sure where to take it for the repair. Any suggestions of good shops ( also the best place to buy a replacement speedometer cable for my 82 ‘Vette ) would be greatly appreciated.

terry82

have you thought about fixing it your self?Its not a hard project.If you feel its best left to a pro ,then most auto shops can handle a cable replacement.i buy a lot of my parts from rock auto.Or I would call Wilcox.

TimAT

Does your car have cruise control? The cruise transducer has a bigger chance of failure than the speedometer head.

theandies

This might help you select the proper gear:

Speedo gear calculator

Big2Bird

I would only add that you want to get the correct gears to get the odometer accurate. If the speedometer is still off, the head needs to be calibrated.

Wrecked82

Agree. Same here. 2.7something to 3.55 rear end, and stock 255/60/15 but shop drove car and checked speed to ensure right gear driver.