speedometer dont work what could the problem be

[chevyon22s]

i have a 92 chevy and the speedometer dont work i changed the cluster and it didn't work the only time it works is when you start the truck it jumps up a little and falls back down and thatwhat could it be?????

 

[Swims350]

sounds like maybe wiring or the sensor in the trans or transfer case if it's 4x4. it's what the end of the wires plug into it's a speed sensor, maybe it's bad, if not then a wire might be unhooked or cut, broken or something. Not unless you got a bad cluster or circuit board.

 

[barebones 1500]

sounds like bad vss. i got the same problem