Speedometer 3x too fast?!

[trscott]

My 1991 FJ80 with 335k miles now is still running like a top, but the speedometer has become intermittent. Sometimes it works fine, but increasingly it reads about 3x too fast. By the time I get up to 35 or so it is pinned at the end of the scale. Oddly, the odometer continues to work correctly even when the speedometer is registering too fast. It is pretty weird to pull out from a traffic signal and see the speedometer register about 60 mph about the time you get across the intersection.

I am assuming this is some sort of electrical issue, since I cannot see how a mecahnical speedometer could have this sort of failure (3x too fast). Perhaps a loose electrical connection that seems to be getting about three times as many pulses as it should be.

I am not sure the failure is precisely 3x. It may vary a bit, but pretty close to 3x.

Any thoughts about what I should be looking at?

I can probably fix it if it is at all repairable, but I have put off researching it because I don't look forward to digging into the dash that far.

If I am going to be in there working on the dash I would probably like to replace all the dash indicators with LEDs.

This truck has been driven on a lot of hard washboard gravel roads, so it has gotten a lot of shake and shock.

Thanks!

 

[jlg32281]

I would check the grounds first.

 

[Michael Hanson]

Go down under the cruiser,follow the speedo cable into the trans.-transfer case. Unscrew the cable pull it out, clean it with a light oil and reinstall. This should help. Mike

 

[thestunts]

It is pretty weird to pull out from a traffic signal and see the speedometer register about 60 mph about the time you get across the intersection.
Thanks!

Slow down turbo !

Subscribed, similar problem for me. Except mine is intermittent and either reads or doesnt read and is at 0, or it bounces around even while maintaining speed.

Keep us posted on what you find ...

P.S. 335k ? NICE !