chevyfiesta

Hi i'm looking for some help troubleshooting a overactive speedometer on my 89 Chevy Van. It reads about 35mph to fast, so when i'm driving about 35mph the needle floats at about 70mph. Also when parked with the motor shut off, the needle sits at about the 35mph mark instead of 0 where it should be.

It was working how it should be about a week ago and this happened while I was out on a drive, it actually seemed to occur right after I was doing some reverse maneuvering in the van trying to back out of a place, if that helps figure out anything. If anyone has had any experience with this type of thing I would sure like to hear from you and what i'm looking at to fix it, i'm hoping to be able to fix it without having to take it to the shop. Thanks!

by the way, odometer works fine.

P20stepvan

my spedo does the same thing, when im going 40, the spedo reads about 65.....
i am almost positive my issue is an incorrect mechanical gear ratio on the trans....

my trans dipstick tube has a "fabrique en canada" sticker on it, so im thinking it might even be a mph-vs-kilo issue with the gear. my van was made in detroit in '77, im not sure if GM was sourcing parts from canada at that time so it may actually mean nothing, but the trans does look like a replacement/rebuild.... its a lot cleaner then rest of drive train....

long story short, is your trans a replacement?.....have you checked the speed gear on the side of trans?... you can get replacement gears in several different ratios to correct problems like this from GM and several different vendors...
a change in tire size can have an effect also...... and lastly, have you done a measured mile to verify the odometer is correct ?

chevyfiesta

Thanks for the reply. I found out that it was the actual speedometer unit. When disconnected from the cable the needle should fall back down to zero on a working speedometer, if the needle doesn't fall back down then thats a sign its the speedometer and nothing beyond it.

So pretty easy fix even for a non mechanical guy like me... took about 20 minutes to replace after I found a used speedo from a Pick and Pull yard. You don't have to replace all the entire cluster unit with all the other gauges. Once you find a match, just take the speedo cluster and swap it with your old one.

Good luck.