I have a FB with the common 2nd gear syncro problem.....will only another FB 5 speed tranny fit??

 

Try a B2000/2200 truck.

 

really?????.....no sh*t!!

I wouldn't have thought that!!

 

Any NA RX-7 transmission from 81(those are non-SA, right?) to 92 will fit, provided you swap the front and rear housings from your transmission on to it (a ~30 minute job).

The internets are not 100% on the piston transmission/rotary transmission compatability. Some people say they're fine (once you swap bellhousing/shift tower as above), others say input shaft lengths are different.

Easiest would likely be to find an NA FC trans, though the gearing may be a little taller/wider.

 

This is a good article on this topic


https://www.rx7club.com/1st-gen-archive-71/transmission-transmission-interchange-information-783499/

 

You only need to swap the tail housing and shift rod to bolt any 81-92 NA trans on. The GSL-SE trans has a taller 5th gear so it's great for cruising on the highway. I just put one on my FB and it went from cruising at 80MPH @ 3500RPM to the same speed at 3100 RPM. Can you say gas savings. 1st through 4th gear are the same ratio so acceleration won't suffer.

 

the earily miata tranny works the same also except you change the front and the tail shaft housing and just keep the main center section. these have the best gears.. closest ratio.

 

you have to mill the input shaft From what I hear.

 

We did the MX-7 swap and it is a much better ratio than any of the RX7 boxes. Its not a lot of work and well worth it! I would use a gear box from a 1999-2005 Miata.

 

Could you comment more on what made it better ratios? Closer, wider, taller, shorter? Myself, I could go for a taller top gear, less gap between 3-4. Is this a 6spd swap (or am I mis-remembering 99-05 Miatas having a 6spd option?).

 

man, a miata 6spd into an FB would rock.