The speedometer cable connects a rotating gear within the transmission or transaxle 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 or transaxle 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 10% is considered normal due to wear and other variables. Stated another way, if you drove the vehicle 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 vehicle for comparison - the other vehicle's 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 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
REMOVAL & INSTALLATION
- Follow the appropriate procedure given previously for removal of the instrument cluster. The cluster need not be fully removed, but only loosened to the point of being able to disconnect the speedometer cable.
- Disconnect the speedometer cable and check that any retaining clamps or clips between the dash and the firewall are released.
- Safely raise the vehicle and support it on jackstands.
- Disconnect the cable fitting at the transmission or transaxle and lift the cable and case away from the transmission or transaxle.
- Follow the cable back to the firewall, releasing any clips or retainers.
- From inside the vehicle, work the speedometer cable through the grommet in the firewall into the engine compartment. It may be necessary to pop the grommet out of the firewall and transfer it to the new cable.
- When reinstalling, track the new cable into position, remembering to attach the grommet to the firewall securely. Make absolutely certain that the cable is not kinked, or routed near hot or moving parts. All curves in the cable should be very gentle and not located near the ends. Note the speedometer cable inside the housing must be lubricated with the proper lubricant before installing it to the vehicle.
- Attach any retaining clips, brackets or retainers, beginning from the middle of the cable and working towards each end.
- Attach the cable to the transmission or transaxle. Remember that the cable has a formed, square end on it; this shaped end must fit into a matching hole in the transmission or transaxle mount. Don't try to force the cable collar (screw fitting) into place if the cable isn't seated properly.
- Inside the vehicle, hold the other end of the cable with your fingers or a pair of tapered-nose pliers. Gently attempt to turn the cable; if it's properly seated at the other end, the cable will NOT turn more than about 1 / 4 turn. If the cable turns freely, the other end is not correctly seated.
- Lower the vehicle to the ground.
- Attach the speedometer cable to the instrument cluster, again paying close attention to the fit of the square-cut end into the square hole. Don't force the cable retainer.
- Reinstall the instrument cluster following procedures outlined previously. Road test the vehicle for proper operation.