The readings on my speedometer make no sense.

Dear Car Talk

Dear Car Talk | Apr 01, 1993

Dear Tom and Ray:

I have a 1980 Mazda 626 with 202,000 miles on it. My speedometer works fine from 0-40, then there's a dead spot from 40-50--that is, I know I'm going 40, but the speedometer says 50. It works fine from 50-65, then, if I go over 65, it shoots right up to 85. Also, when I stop, it stays on 10mph. Is this a bad cable or are the interior magnets bad? Please answer. I can't find two people who can agree on the cause of the problem.

RAY: It's absolutely the speedometer head, Mike.

TOM: Oh, no. It's clearly the cable.

RAY: Well, you still haven't found two people who agree on an answer, huh Mike?

TOM: Actually, it could be both. You definitely have a bad speedometer head. There's no way a bad cable could cause it to read 10 mph when you come to a stop. So there's no question that the head itself will have to replaced.

RAY: But if it jumps around from 65 to 85, that could caused by a bad cable. And since the cable costs about $20, you might as well replace it when you put in the new speedometer.

TOM: On the other hand, you might want to wait on the cable. It will be easier to run the new cable at the same time you put in the new engine. And with 202,000 miles, that ought to be momentarily.

Get the Car Talk Newsletter

Got a question about your car?

Ask Someone Who Owns One