by Mark Nixon » Thu May 20, 2010 8:23 am
First of all, make sure the sensor and wiring is in place and functioning.
Sometimes the speedo sensor, or adaptor, will loosen up and lose contact, or fall off the vehicle altogether, which rips the sensor wiring off.
You also should check the wiring for chafing, or breakage, especially where it passes through wire holders, around the tranny and where it passes by the floor body seam, as it goes up to the engine.
If it's a bad speedo head, the speedometers are repairable, but the parts can be spendy and it may break again right away.
The main culprit in the speedo is usually either the plastic gear on the motor, or the motor controller board.
Sometimes it's just the motor on the controller board.
I have several speedos here that I need to bench test and they are for sale.
CHECK THE WIRING AND SPEED SENSOR FIRST!
Mark.