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Ultimate Guide to Subaru Shift Knobs + Test Results!

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48K views 39 replies 18 participants last post by  AK06WRX 
#1 · (Edited)
This thread is going to be a collection of all the shift knob information I have gathered over the past few years. I want others to add to it also, pics, dimensions, weight, reviews, etc.




THE TEST:
To test 2 types of threads on Polymer (Copolymer/Delrin) shift knobs. See which one is the strongest.

THE PROBLEM:

Simply put, metal shift knobs get hot in the summer, cold in the winter. Although I have many solutions for this, from knob protector booties to wrapped knobs, one good solution is to use a different material. I have been producing the Copolymer shift knobs for some 2 years now. Here is a brief description of the material:

ACETAL COPOLYMER is very similar to ACETAL HOMOPOLYMER (trade name: Delrin, by the DuPont company). Both of these materials have physical properties within 10% of eachother. For example, Copolymer has a compressive strength of 15K psi, while Delrin is 16K psi. Copolymer has a better chemical resistance than Delrin, and slightly less porosity, meaning it has a more consistent appearance. Overall, there is not much of a difference here, especially when considering the use of a shift knob, so we can consider the two materials equal.

The main problem with Polymers is that they are basically strong plastics. Plastic threads tend to get messed up easily compared to metal threads. Cross-threading during installation or stripping during hard use are two common issues myself and my early customers faced when I make copolymer knobs with threads cut directly into the polymer.

In my desire to produce the best all-around shift knob available, I decided to find the best solution to fix the weak polymer thread issue. I began using a brass thread insert that I custom-machined for each knob. I first tried using epoxy, superglue, and loctite to secure the inserts in. The inserts kept coming loose during regular use. I then tried making the hole smaller than the brass piece and pressing them together with glue. This did not help as the insert still came loose.

Over time, I developed the unique brass insert attachment method I call "WC-Lock". The specific technical details of this attachment method will not be discussed, but I will show proof that it is extremely strong compared to polymer threads with no metal threads.


THE TEST

This testing was conducted two outside sources:
  • Dr. Clemow, PhD.
  • Ms Roth, Mech.Engineer

I made 4 samples for this test.
  • 2 samples - copolymer cylinders with standard polymer threads (no inserts)
  • 2 samples - copolymer cylinders with "WC-LOCK" Brass Thread Inserts


Each sample was tested using an identical stainless steel M12x1.25 threaded rod with a pin hole. The samples were all threaded with the Subaru M12x1.25 internal thread into the polymer/brass.

The steel rods were screwed into each sample 0.250 (1/4) inch deep and the pin was attached to the head of an MTS Mini-Bionix servo-hydraulic closed-loop testing machine with data logging software. This machine is capable of pulling approximately 4500 pounds vertically via hydraulics.




The sample was then lowered so it contacted the table of the machine. Heavy-duty steel machining clamps were then used to hold the sample down at 4 locations.




The machine was then programmed to pull upwards at a slow rate. The results of the test showed that the polymer-thread sample (no metal insert) failed relatively early. The 1/4" of threads pulled right out of the knob as shown below:





In contrast, the sample with the WC-LOCK brass thread insert was tested under the same parameters and maxed-out the machine pulling force without failing. This force was 4 times the failure force of the first sample without failing. Here are the pictures:





Data image of the second test:



Here is the graph of the results:




This shows that using a brass thread insert with the WC-LOCK attachment yields a tensile strength MORE THAN four times that of solid polymer threads. You can see in the black line how the polymer thread first failed at about 50mm, and then the second thread failed around 65mm with the third thread breaking around 72mm. The brass continued to increase in load without a failure. An important note is that the brass threads were not damaged by the test and still worked smoothly.

I think it is impressive that they could not even break one of my shift knobs using the machine.

To convert the 17,800N load that the brass thread was subjected to, that is about 4,000 pounds!

You can hang a fully loaded Subaru off of one of my shift knobs without it breaking!



Sure, these values are more than you can inflict with your hand, but you can still easily cross-thread a polymer knob and damage the threads permanently. This test is a good example of the amount of force needed to really damage a good-quality knob, specifically with my WC-Lock insert.
 
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#2 · (Edited)
General Shift Knob Thread Fitments:

  • Subaru manual = M12x1.25
  • Subaru Automatic = M10x1.25
  • Toyota manuals = M12x1.25
  • Toyota automatics = M8x1.25
  • Honda manuals= M10x1.5
  • Mitsubishi, Nissan, Mazda manuals= M10x1.25
  • Mazda automatics = M8x1.25


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Subaru Shift Knob Car Fitments:



  • 5-speed (WRX, RS, Forested, Legacy, etc): The shift knob must have the M12x1.25 thread inside. The shift knob can be for the STi and it will still work. The best type to get is one specifically designed to fit the WRX by having a boot lip on the bottom. The boot lip allows the shift boot to clip onto the knob so it doesn't dangle in the air.

  • 6-speed (STi & LGT Spec-B): The knob must be M12x1.25 threaded inside. The shift knob MUST have a counterbore on the bottom to allow for the Reverse Ring to slide into the knob. If the knob is just drilled out and threaded (without a counterbore), it may interfere with the reverse ring, not allowing it to pull up all the way. Or, the knob will just sit atop the shift lever, adding unnecessary height to the shifter. Also, many WRX knobs have a deep clearance hole drilled in them, so they won't even screw onto the STi shift lever.

  • Automatic 4EAT (Impreza, Forester, Legacy, etc): All auto knobs that are unscrewable must have an M10x1.25 internal thread. The lever is just a plain threaded rod, so basically any knob with this thread should fit onto it. Clearance must be designed into the knob so it doesn't touch the console (only if it is very tall).

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Stock Subaru Shift Knob Info:

2002-2007 Impreza RS & WRX 5-speed:

Material: Black leather, plastic threading
Height: 3.0" (not including boot lip)
Hole depth: 2.65"
Diameter: Oval of 1.8"x2.0"
Weight: 94 grams
Imprinted shift pattern

2002-2007 Impreza 2.5i 4EAT:

Material: Black leather, plastic silver cap on bottom
Height: 5.2"
Hole Depth: 4.75"
Weight: ~100 grams?


2004 Impreza STi 6-speed:
Material: Black leather, red stitching, plastic threading, all black
Height: 2.3" ?
Hole Depth: 1.6"
Reverse ring recess: Yes
Weight: 69 grams


2005 Impreza STi 6-speed:

Material: Black leather, red stitching, plastic threading, clear plastic cap, colored shift pattern
Height: 2.5"
Hole Depth: 1.6"
Reverse ring recess: Yes
Weight: 69 grams

2006-2007 Impreza STi 6-speed:

Material: Black leather, red stitching, plastic threading, clear plastic cap, colored shift pattern
Height: 2.5"
Hole Depth: 1.6"
Reverse ring recess: Yes
Weight: ~180 grams??


2006-2007 Impreza S203 6-speed:

Material: Black leather, red stitching, plastic threading, clear plastic cap, RED colored shift pattern
All other dimensions same as 06-07 STi

2008 Impreza STi 6-speed:

Material: Black leather, no stitching, plastic threading, clear plastic cap, silver shift pattern
Height: 2.5"
Hole Depth: 1.6"
Reverse ring recess: Yes
Weight: ~180 grams??

2004-2007 Legacy 2.5GT 5-speed:

Material: Black leather, plastic cap with silver shift pattern


2004-2007 Legacy 2.5i 5-speed:

Material: Black leather, imprinted shift pattern


2004-2007 Legacy GT 4EAT:

Material: Black leather, brown wood grain center, silver cap on bottom


2004-2007 Legacy 2.5GT Spec-B 6-speed:
(identical to 2005+ STi shift knob)


2004-2007 Forester 4EAT:

Material: Black leather, plastic silver cap on bottom
Height: 5.2"
Hole Depth: 4.75"
Weight: ~100 grams?



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SHIFT KNOB MATERIAL SELECTION

Shift knobs come in a variety of materials, and each has its own advantages. I'll discuss them below.

ALUMINUM:
Aluminum knobs are generally middle-weight knobs, much ligher than steel, a little lighter than titanium, but heavier than plastic. Aluminum knobs are sometimes anodized in a variety of colors, but most come in the pure silver finish. Some are even wrapped partially in other materials (like half-leather on the Momo). Aluminum is a metal, so it is strong enough to have threads cut directly into the material without risk of easy thread damage. Many large production companies with shift patterns on the knobs put plastic threads in them. (Same is true on some mass-produced Titanium and Steel knobs). This allows you to turn the knob until it faces the proper direction so the shift numbers are facing you. The plastic allows you to manually force the thread deeper because it is soft. This does make cross-threading more of a risk though. Aluminum (like all metals) gets hot in the summer, and cold in the winter. This leads to discomfort when you touch it, but I have some solutions for this (discussed later).

Titanium:
Titanium knobs weigh a bit more than aluminum, but are lighter than steel by about 50%. Titanium is an extremely expensive material, so it normally is priced much higher than other similar knobs of different materials. Titanium has the ability to form colors on the surface when heated, so you'll sometimes see them with blue, bronze, and purple colors. Titanium is also a metal, so it gets hot and cold like aluminum.

Stainless Steel:
Steel is a much heavier metal than the others. It normally weighs 3 times more than Aluminum, and 2x more than Titanium. It makes the heaviest shift knobs available for most applications (true for Subarus). Steel can also form colors on the surface by heating. I found that I can control the color change to get bronze, purple, blue, and a gunmetal gray in a variety of combinations. The weight of steel results in a very smooth shifting feel, reducing the notchiness of the shifter compared to lighter knobs. The steel often can make shifting "feel" faster, but unless your arm moves faster, that isn't true. It does help get solid shifts during competitive driving though. Steel also gets hot and cold like the other metals.

Solutions to the Hot/Cold of metal knobs:
I have found several ways to protect your hand from a hot or cold shift knob:
  • A par of driving gloves: must be the right material to provide grip and comfort
  • A leather or alcantara-wrapped shift knob: provides a comfortable area to hold the knob from
  • A shift knob protector 'bootie': slips over the knob to protect it from scratches and protect your hand from temperature


Polymer Knobs (Copolymer / Delrin):
The polymers known as Acetal Copolymer and Acetal Homopolymer (trade name Delrin) are very similar. Derived from the same bonds, they have phyiscal strength and chemical resistance properties within 10% of eachother. These materials are basically high-tech hard plastics that retain their shape and are suited well for use as a shift knob. The material has a very low thermal conductivity, so it will not feel as hot or cold in extreme temperatures. This is because it doesn't transfer as much heat into or out of your hand like metals.

This material is avialable in black & white for delrin, and a rainbow of colors for Copolymer. The material has a smooth finish to it and a very comfortable feel. It basically eliminates the discomfort with hot and cold temperatures.

The major downside to polymer knobs are the weak plastic threads. As shown in my tests above, the polymer is a fairly low strength in tension, and I have personally found it to cross-thread many times in my own use and with customers. To prevent these thread issues, I offer the WC-Lock Brass Thread Inserts on all the Copolymer shift knobs I produce. In addition to making the threads more than 4 times stronger, it also increases the weight of the knob by 20-60% ! The cost is a bit more for these inserts because they are all custom-machined, but its definetely worth it for a much better overall product.



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SHIFT KNOB SHAPES:

There are many shapes that shift knobs come in, especially when considering custom designs. I am going to group them into only a couple categories based on overall geometry:

SPHERE:
The Sphere shift knob is usually considered the most comfortable and more ergonimic. Its possible that many people also think it just looks better. I sell more sphere shapes than any other shape of knob, so it proves to be a fan favorite. The sphere knobs can be shaped as just a ball, or some have a collar below it (specific use on the Subaru 5-speed is a collar to hold up the shift boot). The sphere shape allows your hand to be positioned vertically, horizontally, or angled to hold the knob so it is open for any driving style.

PISTON / CYLINDER:
The piston shape is one that provides mainly a vertical hand position. The vertical nature also helps with feedback to tell the driver which angle the shift lever is pointed (something that a sphere shape does not convey).
Not as many people get this shape, but I find it the best to use in my own car.

CONICAL / TAPERED:
The cone shape is a cross between the sphere and piston, where it has a comfortable rounded surface on top, but a vertical cone section below to hold it vertically.
 
#18 ·
2004 Impreza STi 6-speed:
Material: Black leather, red stitching, plastic threading, all black
Height: 2.3" ?
Hole Depth: 1.6"
Reverse ring recess: Yes
Weight: 69 grams
What, no picture of the 04 knob? I swapped my 05 knob with a buddy with an 04. I can get u a pic, but I dont have the scale to confirm weight. I never liked the plastic top on the 05, and the 04 had a black pastic piece on top. Looks much better in my opinion.

BY the way, love the testing info. Reminds me of the materials testing class I took during my undergrad work.
 
#7 ·
Wow..great testing info!

Guess now I know where I'll be ordering my shiftknob from!! ;)
 
#8 ·
Chris,

Great test and great results. Are you able to do a a test on the knobs with brass insert to determine what sort of strength the insert has when twisted - how much torque you can put through the knob before the insert moves inside the copolymer?

I love my custom knob you did for me (and wouldn't have anything else) but when installing it I wondered how tight I should do it as I was nervous of separating the bond between copolymer and metal.

Chris.
 
#9 ·
You'll never separate the brass from the polymer with one of my knobs. But I can ONLY promise this for a knob I have made with the "WC-Lock" brass insert attachment. This includes pulling, pushing, and twisting, it will never come loose or come out. You'd have to use a saw or some other destructive method to remove it.

Applying high amounts of torque will not make the brass insert loose unless you put thousands of lb/ft onto it, enough to completely shear a pretty significant amount of polymer. I can design a test for this too.
 
#11 ·
Nice write up. Good to see people putting in their time to make a good descriptive and much informative thread. :tup:

Do you happen to do custom knobs? If so, I'd like to talk...


Custom knobs is my whole business! I make all the knobs individually on my manual lathe, no CNC is used like all my competitors. CNC requires a new program to be written to make 1 small change. This costs a ton of time and increases the price on any item, not to mention tying up the machine for a few extra hours or days. Most of the other shift knob manufacturers will not offer ANY customiztion ability besides an engraving or maybe a selection of colors that are pre-made.

I can easily change a knob in basically any dimension to suit exactly what you want because I am not locked into pre-programmed machines. Plus, you get the satisfaction of having THE ONLY ONE IN THE WORLD like it with custom designs. Also, if you have a group of friends willing to get a similar design, you even get the opportunity to get price discounts on bulk orders (I mean only 5 or more so its not that many). If you sell to strangers, you can even make money off the sales.

Click on my homepage to see what I provide:
Lathewerks.com - WC Lathe Werks - Home of the customizable, hand-crafted shift knob!

Send me a PM with your requests. I'm going to write some more knob info below about materials and shapes.
 
#16 ·
I never cut one apart, but what I would assume is that the 04 STi knob is a plastic shell, wrapped in leather with plastic threads. The 05+ knob that is heavier is probably a steel shell, wrapped in leather, but with a plastic thread insert so you can align the shift pattern by twisting it tight (cutting the plastic threads manually)
 
#15 ·
Way impressive article and test set for a shift knob. I used to work for a major shock absorber / strut manufacturer and we ran lots of serious testing on the MTS machines. Excellent work my friend!
 
#23 ·
Give me a sec and I'll go take one right now.
 
#24 ·
Forgive the horrible pic, not plastic, embossed leather.

 
#25 ·
Poor testing is the case here.

How about you actually screw it into the knob all the way down instead of only using one or two threads? You can clearly see the one with no insert wasn't screwed all the way in while the one with the fitting was.

If it was screwed all the way in then the damage would be all the way down not just on the very end.
 
#34 ·
Poor testing is the case here.

How about you actually screw it into the knob all the way down instead of only using one or two threads? You can clearly see the one with no insert wasn't screwed all the way in while the one with the fitting was.

If it was screwed all the way in then the damage would be all the way down not just on the very end.
added

the insert knob doesn't need the bolt threaded in all the way since its metal to metal contact. the insert is farther into the knob making it basically a extension to the bolt throwing the test results off. so no you can't have both threaded into them one or two threads in. How about you take the insert and thread it in or install it into the knob only one or two threads in and then test it.

I don't want to sound rude, but your comments are completely incorrect. All the samples had the steel rod screwed into the knob exactly 0.25" inches during the pull test. The machine is not strong enough to pull them out with a full inch of engagement. Pulling both samples with equal engagement shows the comparison of strength. If they were threaded in 1 inch fully on both, and pulled using a stronger machine, the graph would appear very similar in shape, just with higher loads.

Referring to the picture in terms of thread engagement for the brass does not make sense. The brass threads were not damaged AT ALL during the test, so you can't tell if the piece was in there .25" or 1 inch because it was perfectly reusable after the full load application. The plastic threads were in .25" also, and were torn out. A pure comparison between material strengths.

You can't say the brass piece is flawing the results because it acts as an extension of the steel rod. That is the WHOLE POINT of using brass. It is an extremely better attachment method that is multiple times stronger than not using it.



I frequent this site daily, I just don't check up on all my old threads, so sorry for the late reply A-man. I got your email a minute ago.
 
#26 ·
added

the insert knob doesn't need the bolt threaded in all the way since its metal to metal contact. the insert is farther into the knob making it basically a extension to the bolt throwing the test results off. so no you can't have both threaded into them one or two threads in. How about you take the insert and thread it in or install it into the knob only one or two threads in and then test it.
 
#28 ·
It would because it uses just one itty bitty set screw to hold te whole thing on. If you're driving hard and pull up on he shifter at all, it'll most likely come off in your hand.
 
#29 ·
I've had a bunch of different cars with shift knobs made of nearly every material available. I only like leather. That said, there's nothing leather on your site for the STi (I have an 07).

My DD is a Honda Fit for which I bought this shift knob

which fits my hand perfect (its Honda Part# 08U92-TK6-100B). Can you replicate this for the STi tranny with the reverse lockout ring? I'd want the Subaru "STi" logo in pink instead of a 6-speed shift pattern on top and a different color other than blue stitching holding the leather together (to be decided later if you can do it).

Post it up here or PM if you prefer. Thanks.
 
#31 ·
Can you replicate this for the STi tranny with the reverse lockout ring? I'd want the Subaru "STi" logo in pink instead of a 6-speed shift pattern on top and a different color other than blue stitching holding the leather together (to be decided later if you can do it).

Post it up here or PM if you prefer. Thanks.
I'm guessing this is not something you can do for me then?
 
#35 ·
This thread is wonderful! So many choices. I currently have a deposit with TIC's Kartboy Super Shift Set. Once I get this installed i'm certainly going to pick up one of your knobs and possibly some extensions if my arm keeps hitting the center console on 2 and 4 shifts. Is lighter plastic or heavy stainless more ideal for positive shifts found similar in a Honda S2000? Also, why do some shifters have a buzz under decelaration? Is that weight or material related?
 
#37 ·
Heavy knobs provide a solid, smoothed out shifting feel.
Lighter knobs provide a crisp, direct shifting feel as they don't damp out the shifter vibrations as much. It's all a personal preference. I use a weighted copolymer knob in my car and never wanted to change it in over a year.

The buzzing in the shifter is not a knob issue, it is something within the transmission linkage, maybe the reverse cable inside the lever is loose. The knobs I make will never buzz if installed snugly because they are solid by design. Some knobs like the stock STi one might buzz where the plastic shift pattern cap may be loose.

Did you get my email from your site? Can you help me out with the custom job?
I have replied to all recent emails :)
 
#38 ·
Lots of good info, didn't read all of it, but I'm bumping because I have a custom asian-hand friendly piston with custom thumble dimple indentation that Chris did for me earlier this year. Great products and very knowledgeable machinist.
 
#39 ·
Hey, great writeup!

So my friend gave me an sti boot with the cool trim ring. I put into my wrx and am trying to come up with some ideas on how to get the lip of the boot to attach to the knob. I'm planning on getting one of your sphere knobs sometime in the future, but just have my 07 stock one for now.

Any ideas?
 
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