Any reason my speedo in my auto truck would be "slow"

[Niki]

At 55(indicated) I'm pretty sure I'm going 70. The truck currently and always has had 3. 54 gears and stock size tires. Are there different drive gears, and which one should I have if so. I looked under the truck, and there's no cable, just 2 wires... any way that thing could be going bad? Thanks

 

[AKimmel]

Look to see if someone has removed the ratio adapter. It screws on the transfercase first then the speed sensor. It speeds the speedo up, I believe mine was a 1. 33 ratio.

 

[dpuckett]

If the adaptor is still there and intact, check the drive and driven speedo gears inside the transmission. Mine is loose on the output shaft of my transmission, and causes it to drop speed significantly when I let up on the pedal. Under load, it is accurate.



Daniel

 

[RRothenberger]

My 91 is the same way..... about 15% slow.