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Old 05-17-2020, 12:53 AM   #1
clsmooth
Scooby Specialist
 
Member#: 86394
Join Date: May 2005
Chapter/Region: VIC
Location: Vancouver
Vehicle:
2000 RS Coupe
Blue Ridge Pearl

Default How to fix / save your STI titanium piston shift knob

I couldn’t find any posts or information on anyone else fixing this, so I thought I’d share what worked for me.

Short answer: 18(ish)x1.5mm to 12x1.25mm thread adapter

Long answer: If you’ve owned, or still own, one of these shift knobs, you’ll know that there’s nothing wrong with the knob itself - it’s a nice quality of titanium. It’s the plastic adapter that’s crap.

I don’t complete get why Subaru used a 7¢ adapter for their $125 - $150 knob. My best guess is the shoulder at the bottom, to snap the factory shift boot onto it without hassle.

The problem with them is clocking. You go to put this knob on, get it tight, and notice the STI logo on the top isn’t straight. You don’t wanna turn it back, cause it’ll just be loose, so you instinctively keep turning tighter to line it up. Unfortunately the treads either on the outside or inside of the adapter are now permanently wrecked just doing this. And I’ve never found a part number for just the adapter.

I got mine used in ’07 I wanna say from a former friend’s roommate who had just sold his WRX a few months prior and had some leftover parts. I snatched up this $125/$150 shift knob (depending who and when was selling it) for $40 at the time.
I noticed the threads on my plastic adapter showed only a bit of wear. It went on OK at first, but not 100% really. I got away with using a bit of silicone, but over time I would have to take the knob off and on, vibration and I think from just usage, the treads would slowly get wrecked. Before I got my daily, the last few years I was not shifting aggressively or it’d come off in my hand.

I re-did the interior a bit this past winter and looked into a permanent fix for this. I know the shift’s thread size (12x1.25mm) but I couldn’t quite tell what the thread in the knob is. I understand what thread numbers mean, but not 100% sure how to measure it, and hard to gauge what’s inside the knob. The outer threads on my original, plastic adapter were gone by this point, nothing to measure as it was smooth.

I enjoy the look & feel of this shift knob and wanted to try and salvage it. I set out to find a thread adapter and ordered a few for a few bucks each. The tricky part is I found these things are known by several names depending who you’re talking to: thread adapter, shift knob adapter, thread reducer, reducer, thread busing, bushing and a few more I can’t remember know. It was a few weeks of searching to find ones in the sizes I wanted. Here are the ones I found:

16x1.25mm | 20X1.5mm | 18x1.5mm | Original plastic crap | Knob

(Yes, I coloured in the rings on the logo blue. A personal touch I always wanted to do. Those fill up with a surprising amount of crud over time).
The 16mm one was way too small. The 20mm is just barely too big. The 18mm one threaded in, but was loose the whole way through til it bottomed out. I looked for about a week for a 19x1.5mm one, but couldn’t find anything locally or online. Either the knob’s a 19x1.5mm that’s no one makes anymore, or I’d start going down the rabbit hole of standard or NPT adapters. If someone’s found what it actually is, I’d love to know.

I proceeded with the 18mm adapter. It had a hex-head at one end cause it was advertised as technically meant as an oxygen sensor adapter. I took advantage of this and it helped me clock the knob so the logo would stay straight while sitting in the car.



Can’t really tell in this photo, but I coated both thread surfaces with JB Weld. The 2 are permanently together now.



The negative part about the hex-head was I didn’t want to implant the suggestion in anyone’s head that the knob can be taken off with a wrench, so I rounded the points smooth. More or less matches the knob.



Threaded it on and it sinched into place with the logo straight. I zip-tied my aftermarket shift boot to the remaining exposed threads on the shifter.




It’s been a very long time since I’ve had such solid shifting.
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Old 05-20-2020, 01:28 AM   #2
Zmanwrx23
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Member#: 438620
Join Date: Jan 2016
Chapter/Region: MWSOC
Location: Des Moines, IA
Vehicle:
2006 WRX Sedan
CGM

Default

this shift knob rocks! IMO the best OEM option knob that Subaru offered. I had mine converted to work with a 6 speed. Nice write-up on the rethread process. If you had access, could you press in perhaps a delrin or other like plastic core into the knob and then machine out new threads into that? Could also allow you to machine a boot retainer back into it as well.
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Old 05-20-2020, 10:59 PM   #3
clsmooth
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Member#: 86394
Join Date: May 2005
Chapter/Region: VIC
Location: Vancouver
Vehicle:
2000 RS Coupe
Blue Ridge Pearl

Default

Quote:
Originally Posted by Zmanwrx23 View Post
If you had access, could you press in perhaps a delrin or other like plastic core into the knob and then machine out new threads into that? Could also allow you to machine a boot retainer back into it as well.
Thanks!
I thought about pouring some sort of melted plastic into the knob, but... uhhh, got turned off from plastic. I didn't mind JB welding the adapter into the knob. Most other aftermarket knobs would most likely have a single, 12x1.25mm threaded input anyway.
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Old 05-21-2020, 10:09 PM   #4
DrD
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Member#: 22412
Join Date: Aug 2002
Chapter/Region: SWIC
Location: Albuquerque, NM
Vehicle:
2024 Legacy Sport

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A while back I fixed mine using JB Weld - held the insert in there just fine.
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Old 05-28-2020, 12:43 PM   #5
GoFrogs
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Member#: 507317
Join Date: Oct 2019
Chapter/Region: MAIC
Location: SW Ohio
Vehicle:
2019 WRX
Pure Red

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Awesome. Nice save.
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