How to Perform a Custom Shift Knob Conversion

How to Perform a Custom Shift Knob Conversion for a Different Car

Wouldn’t it be easier if all car makers used the same thread pitch for their shift knobs? Since this isn’t the case, we’ll talk about how to perform a custom shift knob conversion to make your favorite shifter knob fit a different car.

Custom Shifter Knob
Here’s the shift knob when it was installed in my old Scion XB.

I have this very special custom shift knob that was original designed for a Ford Mustang. It’s the typical American muscle ball shift knob, but CNC machined out of solid aluminum. I love the thing.

The neat thing about this particular manual transmission shift knob is that it’s not just a ball. There’s a small shaft at the bottom of the knob that is part of the knob itself. There are no seams or any of that cheap funny business. It’s all one piece. For this reason, this is a shift knob that feels really good in your hand as you can’t feel any seams between the ball and the stick. At only 175 grams, it’s kind of lightweight, which is a shame. It does work well on smooth shifting transmissions that don’t require heavy shift knobs to mask shifting imperfections. Ahem, Miata. See where I’m going with this?

The knob is M12 x 1.25 Toyota manual transmission shift knob thread pitch which also coincides with the 2005-2010 Ford Mustang GT 4.6 and V6 models. As it is, I modified this knob when I original bought it. I didn’t want it in a Mustang, but rather my daily driver at the time, a 2008 Scion XB Gen 2. The thread pitch was correct, but I needed it to go lower, so I drilled it deeper and threaded further using a M12 x 1.25 tap. The shift knob lived happily in my XB until I sold it prior to purchasing my NC Miata.

That alloy shift knob was then in storage for a couple of years. Because I liked it so much I always wondered if I could somehow install it in my MX-5 as an NC Miata Mod. I never did however. I liked the stock NC Miata shift knob so I never bothered changing it out.

It wasn’t until I bought the 1995 RallyWays Miata that I got the urge to swap the shift knob. I don’t like the stock shift knobs in the original NA Miatas. Sorry. I find the shape weird and not very inviting. I don’t hate it. But I don’t like it very much either.

For months I thought of ways of sticking my old alloy shift knob in the Miata but I wasn’t sure how to do it. Mazda Miata shift knob thread pitch is M10 x 1.25, which is a smaller hole than that in the M12 x 1.25 Toyota/Ford shift knob thread I had. If it had been the other way around, I could have just drilled the knob to bore out the hole and then rethread it.

I tried wrapping the shifter shaft thread with Teflon tape and forcing the shift knob on it. That worked, for 5 minutes. Then it got loose, the Teflon tape got impregnated on the shifter thread and was a pain to clean off. I stopped trying for a bit.

Then I started thinking of using an external rethreading coil to rethread the shift knob to a smaller thread pitch. I spent hours trying to find what the outer thread of a M12 x 1.25 Helicoil insert was. Finally, I got a hold of Helicoil in India, or thereabouts. I didn’t get an exact answer of the outer thread pitch for the M10 x 1.25 insert, but they did tell me that the outer diameter of the insert is 11.787mm. The M12 hole is of course 12mm. At 11.787mm, the insert would be loose in the hole. No go. I considered using JB Weld to glue it in, but Helicoils are expensive and usually only come in packets of 100,000 inserts so I decided not to do it.

CNC Machined Aluminum Shift Knob

Then a friend suggested I use a Time-Sert rethreading insert. I couldn’t find information on the outer thread pitch for the M10 x 1.25 Timesert insert. What I did find is that they are cheap and can be bought individually. So, I looked on Amazon and found a 25mm long M10 x 1.25 Time-Sert threading insert. It was cheap. Like 2 bucks or something. I figured it was worth the risk. If it didn’t work, then I could just try to JB Weld it in like I was considering earlier.

When the insert arrived I was pleasantly surprised it matched the M12 x 1.25 thread of the shift knob I wanted to convert, PERFECTLY. I didn’t have to glue it in or anything. I just threaded the Time-Sert into the knob with a finger, then put the knob on the shifter shaft and continued turning. The insert threaded onto the shaft and at the same time threaded completely into the knob. Nice, tight and secure.

I didn’t check the outer thread of the 25mm – M10 x 1.25 Time-Sert to make sure it was in fact M12 x 1.25, but I’m 99% sure it is. It just threaded in easily and smoothly.

Miata Custom Shift Knob Conversion - Toyota Thread to Mazda

I still have to do something about the shift boot, but here it is in the car. Looks lovely. Eventually, a new shift boot will fit around that bottom integrated boot retainer portion at the base of the knob.

Don’t get hung up on the numbers. I went into detail on how I converted a Toyota/Ford M12 x 1.25 shift knob to Mazda M10 x 1.25 shift knob thread pitch but the conversion you might need could be different. You might need to drill to bore a bigger hole in a shift knob and rethread. Or you might need to go down in size using a Helicoil or Time-Sert. My point is, if you have a shift knob you REALLY like and want to use in a different car, there is usually a very ingenious way to convert the shift knob. Worse case scenario, you might be able to use JB Weld to glue a threading insert in. I didn’t get the chance to try that method, but if you do and it happens to work, email me and let me know. Don’t give up, I bet you can convert your shift knob to work.

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