What is the main shaft speed sensor?

Answer 1

The Main Shaft Speed Sensor is also known as a NM speed sensor. This sensor is mounted on the front passenger side of the transmission facing the radiator. It is basically a magnet that helps control how soft or firm the transmission shifts. If your transmission shifts hard or with a jerk, then chances are you NM sensor is either dirty or has gone bad. Remove the NM (main shaft) speed sensor by unplugging the wiring connector and loosening the 10mm bolt on the transmission. Twist the actual sensor back and forth while sliding it out of the transmission. Once out, take a rag and see if it is dirty--it is a magnet and sometimes metal or other debris can get in the way and make it not work. Clean the NM sensor, blot it back in, plug in the connector. Take the negative terminal off the battery, remove the radio (backup) fuse from the under hood fuse panel. Let it sit for 15-20 minutes, then reinstall fuses and connect battery. Start it up. If there is still a hard jerk when shifting, it's time for a new NM speed sensor.