How do I perform an automatic to manual transmission swap on a Mazda RX-7 FB?

Swapping an automatic to a manual on an FB RX-7 is a great project. The factory 3-speed automatic is known to shift way too early—around 4,000 RPM—which completely bogs down the rotary engine's powerband ⁴.

Difficulty: Hard (Requires heavy lifting, potentially custom fabrication depending on the year, and dealing with a notoriously tight flywheel nut).

Before we get too deep, what specific year is your FB? This is critical because for 1979–1983 models, the transmission mount locations are identical between auto and manual. However, for 1984 and 1985 models, Mazda used different unibodies for the auto and manual cars, and the manual transmission mount sits about 5 inches further back ³.

Here is the breakdown of what you need and how the procedure works.

Parts List

Sourcing a complete donor car is usually the cheapest route, but if you are piecing it together, you will need:

• Manual transmission and crossmember
• Manual driveshaft
• Manual starter: The auto and manual starters are different; manual bolts are longer and the gear clearance differs ¹.
• Complete manual pedal box: Swapping the entire box is much easier than trying to hang individual pedals ¹.
• Clutch hydraulics: Master cylinder, slave cylinder, flexible hose, and the short hardline that mounts on the firewall ⁴.
• Clutch kit: 215mm disc, pressure plate, throwout bearing, and pilot bearing.
• Flywheel: (See notes below on counterweights).
• Interior: Manual shifter surround and boots.

Key Swap Procedures & Platform Quirks

1. Removing the Flywheel Nut Once you drop the auto transmission and flexplate, you have to remove the main eccentric shaft nut. You will need a 54mm (2 1/8") socket. This nut is notoriously tight. You can lock the flywheel in place by bolting a piece of heavy angle iron across the pressure plate bolt holes. From there, use a heavy-duty pneumatic impact or a massive breaker bar with a cheater pipe ⁵. Safety Warning: If you are doing this on jack stands, make sure the car is incredibly secure before you start hanging off a cheater pipe, as the leverage required will violently shake the car.

2. Flywheel and Counterweight Selection Manual and auto flywheels are not interchangeable. A stock manual flywheel has the engine counterweight built into it. However, if you choose to upgrade to an aftermarket lightweight steel flywheel, they typically do not have the counterweight built in. In that scenario, you must save and reuse the separate front/rear counterweight from your automatic transmission ⁵.

3. Mounting the Transmission (The 84-85 Hurdle) If you have an 81–83 FB, the manual transmission crossmember will bolt right up. If you have an 84 or 85, standard manual brackets will not align with your auto transmission tunnel. You have two main options: fabricate a custom bracket out of thick flat steel plate with side bracing to bridge the 5-inch gap, or drill out the spot welds on your automatic transmission tunnel and weld in a manual tunnel from a donor car ².

4. Vacuum Lines and Wiring Once the manual transmission is in, you must plug the old vacuum line that ran from the automatic transmission to the carburetor; leaving it open will cause a massive vacuum leak and idle hunting ⁵. You will also need to wire the reverse switch on the manual transmission into the factory reverse light circuit on your harness.

Torque Specifications

I don't have the verified torque figures for the 54mm eccentric shaft nut or the pressure plate bolts for your specific engine, so don't take a number from me on those—rotary rotating assemblies need to be dead-on. Check your factory service manual for the exact specs. The general automotive procedure here is to apply threadlocker if the manual calls for it, hand-thread all pressure plate bolts to ensure they aren't cross-threaded, and then tighten them down gradually in a criss-cross (star) pattern in two or three passes so you don't warp the pressure plate.