The speedometer in my 1997 B4000, 2wd, 5 speed manual, jumps from 0 to 80 shortly after moving. It does this going forward or reverse. When I stop it will drop to 60 but as soon as I start moving back up to 80. Does not appear to go over 80 although the type of driving I do I rarely have the opportunity to exceed 80 kph.

Thee odd thing is, when it was quite cold here (-20C) for a few days the speedometer appeared to work ok. Also, the odometer appears to be accurate.

Any ideas?

 

Sounds like the speedo head but it is possibly the speed sensor on the trans though i doubt it. I would probably change both anyway so i would change the speed sensor first.

 

Yes, I was afraid it might be the head, but I was hoping that maybe it was a gunked up cable or something. The speed sensor seems to be okay, at least it doesn't throw any codes.

Thanks for the reply.