To replace a shifter knob on a truck, first turn off the engine and remove the screws holding the plastic shifter valve cover in place. Slide the cover down, and disconnect the lines to rid the shifter valve of air. Unscrew the jamb nut, remove the original shifter knob, and replace the shifter valve cover. Take the silver ID tab off the shifter knob, and remove the torx bolts under it to displace the shifter knob body.
Place the new shifter knob onto the shifter valve, and tighten the torx bolts to hold it in place. Put the new tab in the top of the knob, and reconnect the air lines. Adjust the shifter valve cover, and secure it to the shifter valve. Start the truck in order to regain air pressure in the shifter valve. Listen for leaks; the sound of an air leak means the knob is not installed correctly.
Before replacing a shifter knob, determine what kind of transmission is present. Transmissions come in 9, 10, 13, 15, 18 and Super 10. The kind of transmission determines the appropriate-size shifter knob.
After disconnecting the air lines, label them with the name of the valve to which they belong. This can be done with tape and a marker and eliminates confusion when the lines are reconnected.
If the shift cover is also being replaced, remove the old shift cover after taking off the original shifter knob. Feed the air lines through the cover, and drop it down over the shifter stick. Tighten the jamb nut to hold it in place.