The 1987 Porsche 944 uses a small drive gear to run the odometer, which keeps track of the vehicle's mileage. Over time, this gear can warp from heat or several of the gear teeth can chip away, causing the odometer to stop running. You can save time and money by replacing the drive gear in your own home, avoiding a trip to the mechanic's shop, where the whole speedometer is likely to be replaced. You can repair the odometer yourself in two hours.
Park your Porsche, shut off the engine and open the bonnet. Disconnect the negative battery cable from the terminal with a socket wrench. Use a flathead screwdriver (cover the end of the screwdriver with a rag) to pry the speedometer out from the instrument bezel. Insert the end of the screwdriver underneath the plastic rim that surrounds the speedometer in the bezel. Apply force until the speedometer pops out from the bezel. Pull the speedometer out and then disconnect the instrument bezel connector wire from its back.
Use a screwdriver to remove the four screws found on the back of the speedometer and then remove the plastic rim from the rim of the speedometer -- use the flathead screwdriver to pop the plastic rim off the speedometer. Turn the speedometer over and use your hands to pull the long plastic button that activates the trip meter reset.
Remove the speedometer needle by turning it all the way to the right and lifting up gently. The needle will detach from the speedometer. Make sure not to apply too much pressure when lifting the needle up, as this could break it. Remove the two screws that hold the faceplate onto the speedometer and remove the faceplate, exposing the speedometer's circuit board. Lift the motor out of the speedometer (leave the wires attached to the back of the motor) and use your fingers to remove the drive gear -- the drive gear is located directly in the middle of the motor. Install the new drive gear in place of the old one and then push the motor back into the speedometer.
Replace the faceplate over the speedometer and secure it in place with the two screws that you removed previously. Reinstall the speedometer needle by placing it onto the faceplate (turned all the way to the right) and then pushing down until it clicks back into place.
Replace the trip reset button on the front of the faceplate by pushing the button back into place (it will click when it's secure) and then press the plastic rim back onto the rim of the speedometer. Reattach the four screws to the back of the speedometer and reconnect the instrument bezel connector wire to the back of the speedometer.
Push the speedometer back into the instrument bezel and reconnect the negative battery cable. Close the bonnet.
You can purchase a new odometer drive gear at an auto parts store.