vetteguy22

My trani is a t56 magnum and am using the stock speedo in my 1970 Vette. I've been running this combo for a few years and it's always been acurate. Just recently it started reading considerably higher than it should.
I've pulled the cable, inspected, lubed and reinstalled it with no luck.
I also inspected the speedo gear in the trani and it looks ok.
Not sure where to go from here.
Any ideas.
Thanks

Rescue Rogers

Did you replace your tires? Other than that the only thing it could be is internal to the speedo itself. If its like the tach, it uses a magnet to move the needle so it could be sticking in that area getting a higher reading.......maybe

vetteguy22

No, same tires. Really haven't changed anything since I built the car several years ago.
It reads high at any speed.
I can be crawling out my gravel road and it reads 20mph when I'm only doing 15rpm in first gear or its reading 90mph on the freeway when I'm only doing 65-70mph.
I was afraid it might be the speedo itself but am hoping there's some way to make sure.

cagotzmann

If it read slower then you would be looking at a possible cable issue or cruise control module if you have one.

Being fast it would point to the speedo unit itself.

vetteguy22

I was afraid of that but is there any way to test for sure?

BEJ

Curious to see responses to this. I have what seems like the same/similar issue. I was on the highway the other day. Speedo said I was doing 90, but I became skeptical when I looked up and saw the Toyota minivan in front of me pulling away.

JimT

Use a variable speed drill on the tranny end of the speedo cable and note any erratic behavior - jumping or excessively high readings,,,,

vetteguy22

Not sure what that will determine. I know the cable is in good condition and know that the speedo is reading fast. Unless there is some way to determine the speed of the drill in mph.