Your car’s speedometer is a crucial component. It’s responsible for telling you how fast you’re traveling. If you have a newer car, your speedometer is electronic, even if the readout is analog. In an older car, it’s mechanical, which means you have a speedometer cable that attaches to the back of the housing and runs down to the transmission and driveshaft.
The speedometer cable spins in time with the transmission and driveshaft. This motion creates an electromagnetic current that is used by the magnet, hair spring and needle in the speedometer housing to display the speed of your car. Because the speedometer is in use at all times when you’re moving, the cable (and other components in the housing) is subject to a lot of wear and tear.
There are many other things besides age that can affect a speedometer cable. These include kinks and bends in the cable, gearbox oil getting onto the cable, incorrect routing and many more. The housing itself is pretty durable and should last for the life of the vehicle, but the inner workings of the speedometer are another story.
Some cars have speedometer assemblies that can be repaired when something goes wrong. Others have to be replaced entirely (the entire housing, including the cable, the magnet, the pointer and hair spring must be replaced). There is no definitive use life for the cable or the speedometer itself, though. Age, use, and damage all play significant roles here.
Given the fact that a problem with the speedometer cable could render the readout inaccurate at best or inoperative at worst, it’s smart to know a few of the signs and symptoms that point to a problem with the system. These include:
- The speedometer needle moves back and forth, without indicating a particular speed
- The needle bounces
- A loud noise is heard from the speedometer housing at higher speeds
- At lower speeds, the needle drops to 0 and then back frequently
- The Check Engine Light is on
- The speedometer needle vibrates
- The speedometer doesn’t work at all
If you’re experiencing any of these symptoms, the professionals at YourMechanic can help. One of our mobile mechanics can come to your home or office, inspect the system and replace the speedometer cable and housing if needed.