How to Fix a Speedometer Cableby Chris Stevenson
The speedometer cable translates the transmission gear speed through a cable housing and up to the speedometer gauge in the back of the instrument cluster. Connected at both ends by two small gears (or slots), the speedometer cable rotates within the housing and tabulates the speed of the vehicle. At times the speedometer needle can bounce, fluctuate and jerk wildly, or there might be no reading at all. Repairing the speedometer cable can be a simple chore if you pay attention to a few repair tips and some troubleshooting advice.
Put the vehicle in park and set the emergency brake. Open the hood. Hoist the vehicle with the floor jack high enough to place four jack stands under the frame next to each wheel. Make sure the vehicle sits level and that all the jack stands have been set at the same height.
Position yourself on the driver's side floorboard where you can look up under the dashboard. Use the shop light to illuminate the area. Where the speedometer gauge sits in the cluster, you will see a large black cable coming from it and angling downward to pass through the firewall. You'll need to use a pair of channel locks or pliers to remove the circular retaining ring on the head of the cable where it joins the speedometer gauge. Turn it counterclockwise until you can remove it with your fingers.
Remove the cable from the cable housing by trying to pull up on the cable end. If it remains fixed and immobile, you will have to move to the engine compartment. There will be a grommet on the firewall through which the cable housing passes. Detach the grommet from the hole and pull the cable housing through, being careful not to bend it at sharp angles. Detach the cable housing from any other guide clamps or wire loom fasteners that lead down to the gear box or transmission housing.
Remove the ring retaining nut from the gearbox or transmission housing. In the case of a small plate and bolt that holds the retaining nut in place, use the appropriate socket to remove it. Once you have the retaining nut off, pull the cable away and place it on the floor. Use carburetor cleaner to spray down inside the housing (either end) and shake several times. This will remove dried grease that has turned to gum.
Pull the cable gently out of the housing with the pliers. Soak the inside of the cable housing again with carburetor cleaner and let it drain. Compare the length of the new cable with the old cable. Make sure they are the same length and have identical slot ends. Lubricate the new cable with lithium grease, spreading a medium-thick coat over all sides of the cable. Insert the new cable inside the cable housing, gently twisting and pushing it until it protrudes from the other end. Wipe off excess grease.
Move to the underside of the vehicle. Align the slot end of the cable to the inside of the gearbox or transmission housing, turning the opposite end of the cable with your fingers until the slot seats. Connect the gearbox-transmission side of the cable housing, turning the retaining nut clockwise until it seats. Feed the cable up through the frame and back through the firewall, making sure that you reconnect it to the guides. Take the firewall grommet and run it onto the cable housing. Push the cable through the firewall hole and secure the grommet back in place.
Connect the retaining nut on the cable housing to the back of the speedometer gauge. Tighten gently with pliers or channel locks. Start the engine and allow it to idle or press the accelerator pedal to bring the engine speed up a little. The speedometer gauge should now register a steady rpm that goes up and down with acceleration.
Remove the jack stands and lower the vehicle to the ground. Test drive the vehicle to make sure the speedometer is working properly.
- When servicing any speedometer cable, always buy the entire kit just to make sure you have replaced all the parts. A cable housing and cable typically come together already greased and ready to install as one unit.
- Be very careful when running the engine while the vehicle sits on jack stands. Running the engine too fast can set up unwanted vibration and cause a stand to slip or the vehicle to fall.
Items you will need
- Channel locks
- Lithium grease
- Socket set, 3/8-inch drive
- Socket wrench
- Floor jack
- 4 jack stands
- Speedometer cable (new)
- Shop light
- Carburetor cleaner
- 2 Car Pros: Repair Topics: Vehicle Speedometer Questions
- "Auto Repair Shams and Scams"; Chris Stevenson; 1990
- speedometer image by Larry from Fotolia.com