How To Install A Speedometer Cable

Today we’re going to show you how to install a speedometer cable. The speedometer in my 1968 Mustang has been loud and incorrect since I bought the car. It was annoying enough that the needle bounced and read 15-20 mph too fast, but after a nine hour trip in the car a few weeks ago the maddening noise of the cable at a sustained 80 mph for hours on end pushed me over the edge. Shortly after arriving at my mother’s house on Long Island I bought a tube of white lithium grease, borrowed a screwdriver, pulled the gauge cluster out, zipped the speedo cable out of its sheath, and lubed the hell out of it. Then, when I attempted to feed the cable back down it bound up about two thirds of the way down, and would not go in.

It always bothered me the way whoever installed the cable last routed it so close to the steering shaft that it touched the rag joint, but that was only part of the half-assery. When I got under the car assuming I’d find a too-tight bend in the cable I instead found it laying on the exhaust, which had burned a hole in the sheath. I put the gauge cluster back in, sans speedometer cable, and used a speedometer app on my iPhone to avoid a speeding ticket on my way back to Virginia.

Now, my car clearly needs a whole new speedometer cable, but yours may not. If your speedometer makes a lot of noise, or the needle bounces you can likely get away with lubricating your existing cable with white lithium grease and transmission fluid. If your speedometer reads incorrectly due to a rear end gear swap and/or non-stock wheels and tires, as mine does, you can fix it by changing your speedometer’s driven gear. We’ll address both of those scenarios during this speedometer cable installation. This is obviously the process for a classic Mustang, but the procedure is similar for many older vehicles with a mechanical speedometer drive.

If your speedometer is noisy or the needle jumps, a simple cable lube might do the trick. Whatever remedy your car ends up needing, the reward is well worth the modest investment of time. A long drive is always nicer when everything is working well.

 

  1. Release the gauge cluster from the dash and pull it out enough to access the back of the speedometer. The 1968 Mustang cluster is held in with a handful of phillips head screws. Be careful you don’t pull wires, plugs, or bulbs out when you move the cluster.
  2. Disconnect the cable from the back of the speedometer. The Mustang cable is threaded on and is easily removed with a 3/4 inch wrench.
  3. Remove the bolt from the cable retaining clip on the transmission end of the cable and pull it out.
  4. Follow the cable from the transmission to the firewall and remove any retention clips.
  5. Unplug the grommet from the firewall and carefully pull the cable through the firewall from the engine side.
  6. Remove the clip from the driven gear and set it aside to be used on the new cable.
  7. Run the new cable through the firewall from the engine side and plug the new grommet into the firewall hole.
  8. Even if you’re starting with a new speedometer cable, it’s a good idea to lubricate it. Soak the cable in clean transmission fluid then liberally apply white lithium grease to the cable. Now, fish the cable back down the sheath as far as it will go.
  9. Screw the new cable back into the speedometer, first ensuring the square cable end is properly set into the speedometer drive. The nut should be snug, but be careful not to overtighten it.
  10. Route the cable from the firewall to the transmission, being careful to keep it away from heat, exhaust, and moving parts. If necessary install a few cable clips to secure the cable.
  11. Install the driven gear on the end of the cable and secure it with the retaining clip.
  12. Push the end of the cable into the transmission as far as it will go. Gently turn it until the gear engages, if necessary. Bolt the retaining clip back in.
  13. Turn the radio down and go for a ride to ensure all is working properly.

 

If your speedometer is reading incorrectly you probably just need to swap the driven gear on the cable. If your gauge is reading faster than you’re going you need to switch to a gear with more teeth. In my case I went from 18 teeth to 20 teeth, which brought the indicated speed closer to actual, but it’s still off about 5mph. I’ve just ordered a 21 tooth gear and will see where that gets me when it arrives. If you have a smartphone there are tons of free speedometer apps available that will allow you to check actual speed via gps to compare to your indicated speed.

If your speedometer is noisy or the needle jumps, a simple cable lube might do the trick. Whatever remedy your car ends up needing, the reward is well worth the modest investment of time. A long drive is always nicer when everything is working well.

 

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By | 2017-09-12T19:01:37+00:00 August 4th, 2015|Auto Projects|4 Comments

About the Author:

I’m a lifetime car guy with a broad interest in just about any type of self-propelled machinery, and racing. I have a soft spot for under-appreciated marques, which often gets me in trouble with oddball projects.

4 Comments

  1. Dan Hankin August 24, 2015 at 2:05 am

    Update: The 21 tooth speedometer driven gear brought the indicated speed to within 2mph of actual speed as checked with GPS. For reference, if anyone with a similar car is trying to correct their speedo I’m running 235/60R15 tires and 3.50 gears.

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  3. Keith January 21, 2017 at 9:10 pm

    This is good information. But my problem actually removing the driven gear. I’m replacing the speedometer due to fire damage on a 70 mach1 4 speed. I have the old cable out, and trying to reuse the driven gear but cannot remove it. I have the retaining clip off but the gear will not come off. What is the trick? Should I just order a new one? I figure if it can be put on it should be able to be taken off.
    Thanks for any help with this.

    • Dan Hankin January 22, 2017 at 6:52 pm

      Hey Keith, thanks for the comment. If it’s original, or even just been on there for a few decades you’ll probably have to put your back into it. There really isn’t much of a trick to it once the clip is out. It should just twist off…but sometimes the old ones are sticky. FWIW though, those gears are cheap and as long as everything is apart it’s not a bad idea, in my opinion, to swap it for a new one. The plastic gets brittle over time.

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