REMOVAL & INSTALLATION
See Figures 1 and 2
The speedometer cable connects a rotating gear within the transmission to the dashboard speedometer/odometer assembly. The dashboard unit interprets the number of turns the made by the cable and displays the information as miles per hour and total mileage.
Assuming that the transmission contains the correct gear for the vehicle, the accuracy of the speedometer depends primarily on tire condition and tire diameter. Badly worn tires (too small in diameter) or over-inflation (too large in diameter) can affect the speedometer reading. Replacement tires of the incorrect overall diameter (such as oversize snow tires) can also affect the readings.
Generally, manufacturers state that speedometer/odometer error of plus or minus 10% is considered normal due to wear and other variables. Stated another way, if you drove the truck over a measured 1 mile course and the odometer showed anything between 0.9 and 1.1 miles, the error is considered normal. If you plan to do any checking, always use a measured course such as mileposts on an Interstate highway or turnpike. Never use another truck for comparison; the other trucks inherent error may further cloud your readings.
The speedometer cable can become dry or develop a kink within its case. As it turns, the ticking or light knocking noise it makes can easily lead an owner to chase engine related problems in error. If such a noise is heard, carefully watch the speedometer needle during the speed range in which the noise is heard. Generally, the needle will jump or deflect each time the cable binds. The needle motion may be very small and hard to notice; a helper in the back seat should look over the drivers shoulder at the speedometer while the driver concentrates on driving.
The slightest bind in the speedometer cable can cause unpredictable behavior in the cruise control system. If the cruise control exhibits intermittent surging or loss of set speed symptoms, check the speedometer cable first.
Some cables do not attach directly to the speedometer assembly but rather to an electrical pulse generator. These pulses may be used for the meter and mileage signal. Additionally, the electric signals representing the speed of the truck can be used by the fuel injection control unit, the cruise control unit and other components.
- Remove the instrument cluster and disconnect the cable at the speedometer. On some models it may be possible to disconnect the cable by reaching under the dash. Some connectors screw onto the back of the speedometer; others are held by plastic clips.
- Disconnect the other end of the speedometer cable at the transmission extension housing and pull the cable from its jacket at the transmission end. If you are replacing the cable because it is broken, don't forget to remove both pieces of broken cable.
- Lubricate the new cable with graphite speedometer cable lubricant, and feed it into the cable jacket from the lower end.
- Connect the cable to the transmission, then to the speedometer. Note that both ends of the cable are square; the ends must fit properly in the fittings.
- Plug the electrical connector into the instrument cluster, and replace the cluster if it was removed.