An erratic speedometer can be repaired by replacing the motorcycle’s speed sensor.
Harley-Davidson Sportster 883 and 1200 models use a special sensor to detect the motorcycle’s speed, providing greater accuracy than the steel cable used on earlier models. This vehicle speed sensor is attached to the engine’s crankcase, behind the rear cylinder and the starter motor. Although the sensor is fairly robust, it can go bad over time, resulting in an erratic speedometer reading. Replacing the sensor is straightforward enough for most Sportster owners to complete on their own with a basic mechanic’s tool set.
1. Grasp the top of the left side cover, located below the rider’s portion of the seat. Pull the upper edges of the cover away from the frame, then lift the cover to separate its mounting tab from the latch built into the motorcycle’s frame. Set the left side cover aside.
2. Pull the cover off of the Maxi-Fuse holder, located along the positive (+) terminal-side of the battery. Pull the Maxi-Fuse out of the fuse holder to disable the motorcycle’s electrical system.
3. Unplug the vehicle speed sensor’s electrical connector, located behind the rear engine cylinder and the starter motor. Unscrew the bolt attaching the speed sensor to the engine crankcase using an Allen wrench. Pull the speed sensor straight out of the engine crankcase by hand.
4. Push a new speed sensor into the engine crankcase. Screw the sensor retaining bolt into place and tighten it to 90 inch-pounds using a torque wrench. Plug in the speed sensor connector.
5. Push the Maxi-Fuse into the fuse holder, then reinstall the fuse holder cover.
6. Slip the left side cover’s lower tab into the frame’s latch. Push the bosses at the rear of the cover’s upper edges into the rubber grommets in the motorcycle’s frame.