Just got this done tonight. I find it hard to believe that there's no one on the Internet anywhere who seems to have done this (or at least written about it). Here's the text, that will make it into the book:
One of the most popular and easiest upgrades for your car is the addition of an aftermarket shift knob. Let’s face it, the steering wheel, gauges, and shift knob are the three main items on the car that you have a personal interaction with. Why not spruce them up a bit – I personally find the Boxster OEM shift knob in particular to be quite boring. The shift knob chosen for this article was the MOMO Shadow carbon fiber, available for about $90 from PelicanParts.com. I also used a black MOMO Endurance shift boot, and the Endurance finishing knob that attaches to the bottom of the shifter. Installation takes about 2 hours, as you need to remove the shifter from the car (unless you have the short shift kit installed). Some slight modifications are needed to the shifter handle to make the aftermarket knobs fit, but this is relatively easy to do.
Begin by removing the existing shift knob off of your shifter (see Project XShort Shift Kit for instructions). If you have the factory short shift kit installed, then all you need to do is unbolt the shifter handle from the inside of the shifter (see the inset of photo 3). If you have the standard shifter in your car, then you will have to remove it (see instructions in Project XShort shift). With the shifter removed, grind down the edges of the shift handle, as detailed in Photo 1. Measure and test fit the knob to make sure it fits on the shaft, and then install the shifter and console back into the car. You also might be able to use sandpaper and/or files to modify the shifter in the car, but that seems like it would be a lot of work and would create a bit of a mess in your interior.
Attach the boot to the retaining frame as detailed in Photo 2. Install the boot, place the finishing ring on the shaft, and then install and tighten the knob using the three set screws at the bottom of the knob. Finally, screw on the finishing ring, and then attach the top of the boot to the finishing ring by stretching the top of the boot over the bottom of the ring. The final result is very professional looking, and looks better than stock!
Picture 1: The factory shaft is just a little too wide to accommodate most of the aftermarket shift knobs. Using a common bench grinder, simply grind a bit of the handle down on each side until the width is about 13.75 mm. Bevel the edges of the handle so that it will easily fit inside of the shift knob, and test fit the knob on the end of the handle (short shift kit shown in the inset photo). Wear gloves while grinding the handle down – it will easily become hot to the touch.
Picture 2: A- Remove the shift boot retaining frame from the existing shifter. B- If you don’t want to destroy your existing shifter, then you can simply order the retaining frame, PN: 996-552-655-01 (cost about $8). C- Wrap the new boot around the frame and test fit it in on top of your shifter. Move the shifter into all of the gear positions 1-2-3-4-5-R and make sure you have enough slack in the boot. D- Poke holes in the boot for the tabs on the back of the retaining frame. E- Carefully cut the excess material on the boot using a pair of scissors. F- Finally, using some 3M or Permatex Super Weatherstrip adhesive, glue the edges of the leather to the retaining frame.
Picture 3: Here’s the finished product. The shift boot finisher shown in the photo is chrome, but it’s also available in black and silver as well. The final installation looks very professional – as good or better than stock! The inset photo shows a short cut that you can use if you have the short shift kit installed. Simply unbolt the center shifter from the metal housing and remove it so that you can easily modify it on your workbench.