Being a man more interested in cars from the 1970s on back, I’m accustomed to pulling a speedometer cable out in minutes for a quick cleaning and greasing; however, the job isn’t quite so straightforward for “new” cars from the 1980s. The noisy speedometer in my dad’s 1988 Mustang GT convertible had long been an annoyance, and the most common repair is to replace the entire cable assembly. While a complete new cable is a bargain at right around $25, replacing it takes up more of your day than you might expect.
My parents live nearby, so I drove down to their house and picked up the Mustang to bring it back to my garage where all my tools live (and where my parents couldn’t hear my cursing at their car). Pulling a speedometer cable out for greasing isn’t a practical task on a Mustang of this vintage, which is why I learned that it’s a smart play to install a new one, but that requires disassembly of the gauge cluster (and more).
There were a few points in the job where I was too engrossed, or too alone, to take pictures, so I’ve substituted photos from Late Model Restoration’s website.
Fortunately, the Fox Body Mustang is so popular that this is one of those rare times when a YouTube video could help me out. Late Model Restoration, the online store where I bought the cable itself, posted a succinct six-minute video that taught me the basics without getting into too many details that I could figure out on my own. First, I removed the collar around the steering column, which involves three screws that engage in plastic. It’s not the best system because 38-year-old plastic is brittle.
Then, I removed the underdash plastic to reveal some of the screws that hold on the gauge cluster fascia.
Before removing all the fascia’s screws, I used a flat-blade screwdriver to gently unclip the switches for headlights, fog light, four-way flashers, and the convertible top. It’s all made of plastic, folks.
Once the switches and the fascia were removed, this is what remained, the instrument cluster itself.
The speedometer cable isn’t held to the head by the old-fashioned screw-on barrel, but rather a plastic clip that requires a squeeze to remove.
Then, there are two wiring harnesses that connect to the printed circuit behind the cluster that also require removal. The wires weren’t quite as long as I would have liked, so I couldn’t get a really good look at them; working by feel was the only way to do it.
Once the cluster was out, there was that momentary sinking feeling that I’d taken the car apart more than I had bargained for.
The cable itself is attached to the firewall with a big grommet. The new cable came with the grommet for a manual-transmission car, which passes through a different hole in the firewall than it does on an automatic-equipped car like my father’s. On stick cars, the clutch cable passes through this hole, so I had to buy the grommet for AOD cars, which costs about six dollars.
The cable is held to the front subframe with a clip and a sheetmetal screw, and to the floor with this spring clip.
Finally, the speed sensor enters the back of the transmission and is held down by a clip that’s attached to the transmission with a small bolt.
After all that, I was able to extract the greasy old cable from underneath the car and go about swapping little bits over.
A funny little clip holds the speed sensor and speedometer gear to the cable, so I removed them to transfer them to the new cable.
I also had to slip the new grommet over the new cable before attaching the speed sensor, and I also swapped over the subframe clip. I cleaned up the speed sensor and wrapped the job up; installation, as they say, was the reverse of removal, so there were no big surprises.
This is a greasier-than-he-expected-to-be backyard mechanic who is happy that he got the job done.
I took the Mustang out for a trip up the highway to make sure the speedometer was quiet, and thank goodness it was, because the only other culprit would be the speedometer head itself. The needle still has a little bounce at low speeds, but it’s accompanied by silence, at least from that corner of the car. Now about some of that other deferred maintenance…maybe next year.
Related Reading
CC Tech: 1988 Ford Mustang GT – Plastic, A Better Idea In Quarter Windows (by me)
Curbside Capsule: 1991 & 1988 Ford Mustangs – Home For The Holidays (by Joseph Dennis)
Exactly. At which point you’re happy that you didn’t decide to just squeeze in this task on an otherwise busy day. Unless of course you did.
Great write up, Aaron. Coming from a person who is frequently challenged by performing procedures in the correct order of operations, the part that sticks with me is the necessity of assembling all of the clips and grommets correctly on the cable before starting to reattach it to the car. I just know that I’d forget putting something on beforehand and then have to take it down and start over again, thereby lengthening the job.
Thanks Jeff…you’d have probably been OK in this situation. You could always slice the grommet vertically with no ill effects, and the subframe bracket can be opened up to get around the cable. No sweat!
Thank you for this public service announcement. I have recently been musing about the wisdom of finding something from the 80s or 90s to serve as a combo daily driver and hobby car/truck. You have slapped me back to sanity with this reminder that there are approximately 600 hard to access plastic components that are 35+ years old and are just waiting to fail.
Something I did forget to mention is that the two plastic tabs on the speed sensor broke (they are under the car and subjected to heat and weather, so no surprise). You can get the wiring harness end fairly inexpensively, but I didn’t have it at the time, and the car doesn’t get driven much, so…I wrapped the connection in electrical tape. Worst case is that the cruise control probably won’t work if it comes undone.
There seems some irony in the fact that there’s a speed sensor which presumably sends some electrical signal that could be used instead of a mechanical cable. I presume on modern cars it’s all “speed by wire” … or is it even wireless?
I don’t have a ton of experience working on new cars, but I can’t imagine anything still uses a mechanical cable. They were well on their way in 1988, I guess, even if the Mustang only used it for the cruise control. Actually, I wonder how cars such as my ’87 Thunderbird, which had a digital speedometer, made that all work. I’ve never really thought about it.
Modern cars use a speed sensor that transmits data to the ECU. On S550/650 Mustangs it is my understanding that dashboard speed is calculated from the rear wheel speed sensors (used also by ABS/TCS/ESC). Indeed if the wheel size is changed significantly from stock, the ECU needs to be re-calibrated, otherwise the speedometer will be off.
Unfortunately too late to help but for others who may come across this no need to remove the speed sensor from the transmission. Just undo the clip and slide the cable out, leaving the sensor in place and wires connected.
I think I still might have removed it; that clip isn’t very intuitive (at least to me), and it was a lot easier to figure out once the whole assembly was outside of the car. I’m sure once you’ve done it once or twice it would be a snap.
Reminds me of an article by a car journalist restoring his 1970s Mk3 Ford Cortina and having an awful time replacing the ventilation fan that was installed within the car’s dashboard. He came to the conclusion that ‘The blower unit was hung on a piece of string at the factory and the car then assembled around it’.
Same with the heater blower in 240 Volvos
My Jaguar XJ8 was similar -$1200 to replace the wiper motor, mostly labor.
I figured I would swap out the factory radio with a better unit on my ’69 Datsun 510 only to find it was installed from behind. This meant removing the glove box, and one of the dashboard braces. At least this saved it getting stolen when the car got broken into.
I’m reliably informed that the Rover 200 (P6) was built around the ignition switch…..
It was mounted behind the glove box, but on my pre-update Mark 3 you accessed it from under the bonnet – from memory it was just a matter of four (?) screws and a wire connector, then it lifted off.
What a beautiful old Mustang .
I did the same job (dash binnacle out) in my 2001 Ford Ranger, the total amount of little sheet metal screws was daunting but after making sure every one went back in there’s still no rattles / squeaks in the entire dash .
Any time I take a binnacle out on my own vehicles I take the time to ever so carefully / gently remove the clear plastic “glass”, clean and polish it inside and out then I clean the dust out of the gauge faces and replace all the light bulbs just because they’re 20 + years old and I don’t want to do the job twice .
For those who love to tinker and fix things, holding the end of the speedo cable _up_ and dribbling graphite oil down it will usually do the trick .
If you have a really old one you can withdraw the center out of, clean it well then work graphite grease into it before re assembling .
-Nate
We will need to compare soon, maybe. I did the cable on my 91 Mazda 626 which is extremely similar but with one twist. Now Nate mentions dribbling graphite in but that can’t fix a cable that turns out to be snapped internally.