Anybody know what all the differences are between an SA and FB gearbox, because I'm hitting something in the conversion of a FB to SA gearbox.

* shifter position + tail housing
* shifter is moved up to the outside more in the fb version
* wall of the rear drive switch is less thick in the fb version

 

Well there is no single "FB" version as such because there were further changes introduced in 1984 with different gearboxes for 12A and 13B. In effect, you have 5 major variations: series 1, series 2 and series 3 12A, series 3 12AT and series 3 13B type gearboxes. The series 3 type are very similar to the series 4 NA and Miata (smooth case) gearboxes.

This is what makes the "FB" nomenclature misleading. There is no such thing as an "FB". 81-85 were just designated that in some markets - but importantly not Japan where all 1st gens are SA22C. It is better to refer to the cars by model year or early/middle/late (to use the Japanese naming system) or series 1/2/3 (as we call them in Australia).

The main differences with the series 3 type is that it features different diameter flywheel and clutch, softer cut gears, larger output shaft, plus notably different gear ratios as follows:

Series 1/2:

1st 3.674
2nd 2.217
3rd 1.432
4th 1.000
5th 0.825 / N/A (some series 1 cars only had 4 speed transmissions)
R: 3.542

Series 3:

1st 3.622
2nd 2.186
3rd 1.419
4th 1.000
5th 0.807 (12A); 0.758 (13B)
R: 3.493

There's lots of great info here: AusRotary.com ? View topic - Everything you would ever want to know about Mazda gearboxes

Depending on which series gearbox you have you may need to change the flywheel and clutch to suit.

 

Let's start with the tail:
SA

FB


Forks:
SA

FB


Gear lever thingie:
FB/SA


Ow and they changed the shifter rod also of the 5/R gears

 

PJ and I (among others, info is in the parts catalog), have discovered that the gearbox is NOT SA or FB, its more complex than that.

there is an early SA box, that is unique.
there is a late SA box, which is an FB box, but with an SA tail housing.
there is an early FB box, which is the late FB box and FB tail housing.

all three of these use the same gearset, but the shift linkage is early SA or late SA/FB

there then is a middle FB box

and then the 84-85 FB boxes. (then the 86-87.5, then 87.5-88, 89-91, 89-93 miata, 93-05 miata, 06-15 miata, plus the 78-93 trucks, rwd 626, etc)

 

Why can't they keep it simple

Maybe I can swap the gearbox for an electric motor so I got a direct drive :clownface:

 

its actually not too bad, its just that the transmission change points don't match the year/model change points all the time.

Ford actually does this a lot, in fact most of the time they will introduce a new body style, and carry over the old engines for a year or two. or the reverse, the old body gets the new engine for a year. its one of the few things they do that actually makes some sense. Mazda always has a clean sheet of paper new car, and then a bunch of teething problems. Fords approach lets them sort the engine separate from the chassis/body, although they don't seem to care much if it works or not