Transmission: Plug-n-play

The Miata transmission is adapted with off-the-shelf parts to form a bolt-in solution for the FE3 engine swap.

The five speed transmission that comes in the Miata is plenty and cheap. When I started this project I had three of them so it made sense to use one with the FE3 swap given the cost: $0. Even buying one used isn’t a huge financial set-back, as they usually come up for around $150. In addition to the small price, the five speed is also a complete bolt-in solution. The biggest job is swapping out the Miata transmission’s front section with the same from a Mazda B2000. Since the Mazda truck came with an F series engine and used the same center section/case, the front section swaps out directly with the Miata piece and bolts up to the FE3.

Pulling the transmission’s front section is a matter of removing the bolts that run from the rear of the center section, and then using a puller to separate the case. There are tools made for the job, or a DIY puller can be constructed using nuts, bolts and some steel scrap.

The junction is sealed so the process does require some effort, but once the seal is broken, the sections separate quite easily.

With approximately 2,000 miles on the transmission since installation behind the FE3, it started to show signs of fatigue. There was a new noise that was growing louder which I took as a warning and swapped it out for the spare. Once out the input shaft was noticeably more difficult to spin, requiring two hands with significant effort vs. a single hand with far less oomph for the replacement transmission.

Once the front of section Miata’s transmission is removed, the small gears and shafts are exposed. Given the small size, I think it faired well for going 150,000 miles and then being put under 250+ ft.lbs. of torque for 2,000 more miles. The front section houses the bearings that support the shaft ends.