It's hard to imagine that an item as simple as a speedometer cable is responsible for informing you just how fast your car or truck is going. Not much thought is given to them, though we all know that our speedometer isn't controlled by magic. This cable travels from the transmission all the way up to the gauge in our instrument panel. But how does it work, and how could it fail? The most common reason for speedometer cable failure is that the ravages of time and lack of lubrication have caused it to fray or break internally. Or, as happens less frequently, while driving off-road one could encounter an obstacle that rips it off the transmission. Either way, you can't drive around forever without knowing how fast you are going. It is dangerous, and at the very least you could get a speeding ticket because you don't know if your vehicle is exceeding the speed limit.
Speedometer cables have been around for over 100 years, and have operated mostly the same way until the 1980s
. They are a wound or braided metal cable inside a sheath or housing that can rotate freely inside it. A small gear inside the transmission essentially rotates at a speed relative to the vehicle's speed, and it turns the cable. The cable turns the speedometer itself... but that doesn't move the needle. At the speedometer is a magnet that spins inside an aluminum cup creating what's called an eddy current. That current generates a torque on the needle hub that pulls it against a spring. As the spins get faster, the current gets stronger and the needle goes higher. Digital speedometers use all electronic signals generated by a sensor at the transmission output shaft. The data from that sensor is then sent to the engine's ECU where it is processed into a velocity that appears on your speedometer. While these types of speedometers are new and efficient, eddy current speedometer cables are still more popular.
Replacing your speedometer cable is not a complicated procedure. Remember that if you have cruise control, automatic transmission, column shift, etc., the vehicle options will affect how long it is and how it connects to both the transmission and the gauge. As long as you buy the correct one, it will install with a breeze. The connections at each end are either threaded or press-on. Sometimes they require a clip, so be sure you don't break it when putting it on.
Please do yourself a favor and buy that speedometer cable you so desperately need. It would be a shame if you got a speeding ticket for driving 10mph over the limit, and it could have been prevented if your gauge was working. And why wasn't it working? Because you didn't get a replacement speedometer cable from CPD. Our parts are made from top name brands manufacturers; the same you'll find in the auto parts stores but for a fraction of the cost. So why wait, buy today.