Finishing the 3D printed TPU Shift Knob

After using the TPU shift knob for over a year, I decided it was time to finish it, including bonding the knob to the threaded steel tube that attaches it to the shift lever in the truck.
I had tried several adhesives to fasten the knob to the tube, but I couldn't find anything that didn't eventually break free. I also wanted to sink the tube farther up into the shift knob than the built-in hole allowed. Seeing as the material melts for 3D printing, I figured heating up the tube would allow it to melt it's way deeper into the knob. Also, the melted TPU material would likely bond to the knurled finish I has applied to the outside of the tube.
This all worked as expected, after first clocking the knob on the shift lever and making alignment marks. This way, when the knob is screwed down firm onto the shift lever, the shift pattern on the top of the knob is oriented properly.
I finally settled on using a clear shellac finish over the filed and sanded TPU surface. I applied a total of 3 coats of shellac and that left a semi-gloss finish that felt good in the hand. I like the TPU material for a shift knob. If doesn't get too hot to touch if the sun shines directly on it. Likewise, on a cold winter morning, it almost instantly warms to the touch. It also has just enough internal vibration damping to silence any vibrations that come up the solid steel shift lever that I run in the truck.
I have a B&M short throw shifter, that I installed in the truck over 20 years ago. That shift lever is solid steel, so is prone to transmit vibrations from the transmission. This is different than the factory shift lever that has a vibration damping center section:
www.4crawler.c...
I never liked the included knob as it's solid metal and in the winter, it's very cold. Plus it has no shift pattern on it.
Now I realize the reason for the evolution in the Toyota shifters over time. The early (pre-83) shifters were plain steel rods. Then they went to the 2-piece design with the rubber bonding in the middle:
photos.app.goo...
Not sure if all the shift knobs were made out of a rubber material, but those two features worked in tandem to dampen out noise and vibrations from the transmission from coming up into the cab.
I re-printed the same 3D model as before:
www.thingivers...
but this time in TPU filament. At 90% infill, it seems to make a decent feeling part. It has a similar feel to the factory knob and also dampens out all the noise. I heated up the internally threaded steel tube and pressed that deeper into the knob for a final installation. I did try using a butane torch to smooth out the surface but that didn't seem to have any beneficial effect.
Nice simple design, has the proper shift pattern and I think this one can be adapted to be a replacement. I added one of our shift lever extensions to be able to thread it onto the Toyota shift lever. This is an internally threaded steel tube:
www.4crawler.c...
Subscribe for more content like this
Comment, rate, share & click the bell icon
And as always, thanks for watching

[@The4Crawler]

I find the TPU material is an excellent replacement for the OEM rubber shift knob. It helps to dampen out any noise or vibration that comes up the shift lever while driving. I never appreciated that aspect of the original knob. In the Toyota W56 and other transmissions, the stick comes right out of the gear box where the end is in contact with the various shift gates.

[@cbh148]

For some reason, the factory rubber shift knob in my '88 Xtracab DLX 4x4 (22RE) turned sticky in the last year, but the one in my '87 4Runner DLX (22RE) didn't. It's like the rubber suddenly reached some critical point where it's sweating out stickiness or breaking down or something.

[@The4Crawler]

My old '85 knob never turned sticky. Instead, it started cracking and after a few repair attempts, it cracked into two pieces. But I have seen other rubber parts get that sticky surface.
I'm sure there's a technical explanation of what's going on. I like to think of it as the plasticizers in the material working up to the surface to produce the sticky feeling. Or that material dries out and leaves the rubber hard and brittle.
I've seen this with rubber body mount bushings. Some are dried out and cracked throughout while others are almost like jelly beans, soft and squishy inside with a harder surface. And then there will be some that look and feel like new.