Speed limits are there to help provide better safety on the road. They’re not set arbitrarily. You need to know how fast you’re traveling in order to ensure that you’re both safe, and in compliance with the law. The speedometer shows you the information you need.
Older style speedometers use a cable that runs from the back of the speedometer assembly to the transmission. Newer styles don't use a mechanical cable – they’re electronic. The shift from mechanical to electronic was largely done because of the propensity for mechanical speedometer cables to stretch and eventually break, which would render the speedometer itself useless.
In a mechanical speedometer setup, the cable is in use every time your car is in motion. If the wheels are turning, the speedometer cable is working, transmitting motion from the transmission mount to the needle so you know how fast you’re traveling.
There is no particular lifespan for a speedometer cable, and yours could theoretically last the life of the car, particularly if you don’t drive very often. However, if you drive frequently, you’ll put additional wear and tear on the cable and it will eventually stretch, and possibly break.
Of course, if your speedometer is acting up, it could be another component in the system. Mechanical speedometers also include a magnet, springs, pointers and other components that can experience wear and tear related failures.
Given the importance of the speedometer and the chance that it will eventually fail on you, it’s wise to know a few of the most common symptoms to watch for. These include:
- Speedometer needle bounces
- Speedometer makes a loud noise, particularly at higher speeds
- Speedometer doesn’t work at all (most likely a broken cable, but it could be other issues)
- Speedometer wavers between different speeds (different from bouncing)
- Speedometer routinely displays speeds higher or lower than true
If you suspect that your speedometer cable is stretched or broken, YourMechanic can help. One of our mobile mechanics can come to your home or office, inspect the speedometer, and make any repairs to the speedometer cable if needed.
This article originally appeared on YourMechanic.com as How Long Does a Speedometer Cable Last?.
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