Will an 81 five speed bolt directly into a 79 SA 12a with a four speed?

 

No. The location of the shifter is a few inches forward on the 79-80 SA's compared to the 81-85 FB's.

I don't know if a tail-section swap could fix this, but it's not a direct swap.

 

there is a vin split, and a late SA basically has the same guts as the FB, so the tail housing swaps.
obviously we can look it up (or wait for Peejay), but if you take yours apart and it has roll pins holding stuff together you're good, if there are bolts its not a direct swap

 

Ha!

The VIN split is something like March '80, transmissions made after that have roll pins and you can swap tailhousings.

The difference between roll pins and bolts holding the shift fingers to the shift rods is because the main shift rod in the '79-80 trans and the main shift rod in the '81-15 trans are in different locations, so the shift fingers that the main shift rod engages need to be transferred along with the tailhousing. You can't mix and match bolt-type and roll pin type parts.


If you just want an overdrive transmission, the 4 speed and 5 speed are identical except the 4 speed has spacers where 5th gear is on the 5 speed. Fuel economy is pretty much the same, slightly better with the 4 speed, Mazda only put 5th gear there because at a time when most engines stopped making power around 3500rpm, it was a hard sell to have an engine that cruised at nearly 4000rpm at 55mph.

This does, however, require that you find a pre-80.5 trans to scavenge parts from, so maybe not the best option compared to just using that transmission.

 

yeah, it's too bad it won't work, I found a great deal on a low mileage 81 5spd fairly close to me, and it is nice to have 5th for long trips, so maybe a 79 will turn up at some point?

 

Any '79-80 trans will work. For that matter, so will a ribcase 5 speed from a '74-78 RX-3/4/5, but those are not exactly easy to find either.

If you manage to find a late 80 trans, even if the trans is shot, you can use its tailhousing and shift fingers on any FB or nonturbo FC trans. I forget the vin split, my '80 was 608250(*) so the vin split was probably in the 604,000 range.

* - That car got scrapped in 2001. I still remember the VIN.