I put a 145mph cluster in my car a while back and I had to take the speedo needle off to swap the odometers. When I first tried putting the needle back on, I turned the key to the on position (where all the needles move) and put the needle pointing at 0mph. As soon as I stuck the needle on there it moved itself up to 5mph. So I pulled the needle again and I put the car in gear and idled down a flat street and stuck the needle on pointing at 5mph and it seemed to work. But recently I checked it with a GPS, and my speedo seems to show the correct speed until 40-45mph, then it gets about 5mph off (and I've had the car up to 85mph).

So, did I put the needle on wrong?

When I get some time, I'm going to figure out some way to see if the odometer is right.

 

Do you have stock size tires, original rear end gears, and original transmission? Changing any of those things can make the speedo inaccurate.

 

I have 275/40/17 tires, which should be .3" smaller than stock. The tire size calculator says they will put the speedometer 1.3% fast (speedo shows 60 when I'm really going 59.2). My car came with 3.23 gears, and it has 3.73 gears now, but I put in a 43 tooth driven gear that should have corrected that.