We know Miata manual transmissions and their shifters pretty well from our experience in building super high quality aluminum and bronze racing bushings.
The Miata transmissions are limited to only four types: 1990-1997 NA type 5-speed, 1999-2005 NB type 5-speed, 1999-early 2001 NB type 6-speed, mid-2001 - 2005 NB type 6-speed. The 1990-1997 will have a few changes throughout the years, but all internal and nothing you'll be able to see from the outside. It's said that Mazda improved the transmissions in 1994 for the updated NA8 drivetrain. The big change came in 1999 when the NB chassis arrived. Mazda redesigned the transmission and it is the transmission of choice for Spec Miata racers, as it shifts smoother and is stronger. In 1999 through early/mid 2001, Mazda offered a 6-speed transmission in special editions. This 6-speed was produced halfway through the 2001 model year, so things get tricky when you're looking for parts for a 2000 or 2001 6-speed Miata, as you'll need to know which version of 6-speed you have. The biggest difference to note is the use of the 5-speed shifter and shifter bushing, whereas the mid-2001+ 6-speeds use a larger diameter shifter and larger shifter bushing (which is why we make two different versions of 6-speed bushings). The 6-speeds also do not hold transmission fluid in the turrett like the 5-speed's.
Here's the easiest way to tell the 1990-1997 NA transmission apart from the 1999-2005 NB transmission. The NA will have a smaller diameter mouting base for the shifter, and more obviously it will have an exposed rod on top. The NB transmissions will not have the rod, but rather a "box" on the top where the rod is on the NA's. It also has a larger shifter mounting base. Take a look at the picture and you can clearly see the differences:
There's a surprising number of parts related to the Miata shifter, and buying parts for rebuilding these shifters can be a little confusing to those that haven't done this before. We hope to help out those uninitiated with the Miata shifter by sharing our experience and knowledge of them:
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