How to Repair a Speedometer
If the odometer or the speedometer systems in your vehicle break down for one reason or another, you'll need to repair the speedometer before you can continue to safely operate the vehicle. A broken speedometer makes driving safely very difficult, as you have no idea exactly how quickly you're going. It also makes you more prone to driving too fast, which can result in expensive accidents and traffic tickets. Before you consult with a mechanic and investigate purchasing a new electric speedometer gauge for your vehicle, consider whether or not you'll be able to repair the speedometer instead. This option is typically easy and almost always quite a bit cheaper than the alternative.
Diagnose the Problem
The first thing you'll need to do in order to accurately repair your speedometer system, is to identify what the problem is exactly. The odometer and the speedometer are connected by a system called the speedometer gauge, which exists underneath the dash of the car. In order to access this, you'll have to first disconnect the negative end of the car's battery cable from the battery to short circuit the electrical systems in the vehicle. Next, use a screwdriver with a flat head to pry the cover gasket off of the speedometer gauge. Be careful so as not to break the gasket or the covering. Remove the gasket and set it aside.
Remove the Gauge
Next, you'll need to remove the gauge that holds the speedometer section in place to the speedometer and odometer gauge system. This connects behind the face of the odometer in most cars. Reach around behind the odometer and feel for the wire connection, then gently remove the wires from the back face of the odometer. It should come out cleanly in your hand.
Examine the speedometer for signs of broken gears. The most common cause of a damaged speedometer is a broken gear mechanism in the rear of the face. If this is the case, you'll need to replace it with a matching gear mechanism. These are available at the dealership that specializes in your car or at a variety of different auto body shops. Or, you can purchase one off of the Internet as well.
If there is another component that's damaged, you may have to replace that one instead. Alternately, if you don't see anything the matter with the speedometer, take the system to a specialist to get a second opinion. In the worst case scenario, you'll have to purchase an entirely new speedometer face and system, which you can then reconnect to the odometer gauge and reinstall in the car. This is less expensive, however, than buying an entirely new speedometer gauge from the outset.
If you have any additional questions about the process of repairing a speedometer, consult with a mechanic who is familiar with your particular vehicle in your area.