alright guys and girls. I got a 88 se 5spd and my 3rd gear syncro is already scratching and just a couple of days ago tis been popping outta second when i leave it in there without holding it. what i need to know is why is it throwing it outta 2cnd gear. and also will a 12a tranny work in my car?? i have heard about putting my 13b bellhousing or some crap on the 12a and using that tail housing and everything will bolt up. cause i can get one of those for like free. and i heard it actually is shorter gears or something. gimme your inputs. this tranny is a B**** to drive!!1

 

come on someone this is important!!

 

13B bellhousings do not "unbolt"...well some do, but only on S3 cars, that I know of. You'll have to find an S3 13B bellhousing and then swipe a 12A tranny...but if you pull the S3 bell housing why not stick with the S3 tranny? All the FB trannies are geared about the same aren't they?

 

I swapped an '84 12A FB tranny into my FC last fall. Just put it back on the road a couple weeks ago after winter storage. I'm really happy with the swap so far. It pulls beter first through third, especially in second!

You don't have to pull gears off shafts, the center section of the N/A RX-7 tranny family are the same, as is the length from input to output shaft. The differences are in the ratios, bellhousing, extension / shifter housing, and internal refinements (like synchros). The '84-'85 are the best candidates for swapping, as the earlier models are weaker and have even shorter gearing.

Here's the ratios:

1984-85 12A/13B 1986 - 1990
1st 3.62 3.48
2nd 2.19 2.00
3rd 1.42 1.36
4th 1 1
5th .807 / .758 .697 (gxl) or .711

Felix Miata has lots of good info here:
http://members.ij.net/mrmazda/interc...html#TRANUSAGE

also check out:http://miata.net/garage/tranny_rebuild.html

And of course read the FSM. The '89 FSM has better pictures & descriptions concerning transmission rebuilding.

Basically, what you'll do is split apart the tranny into the three main sections, then put it back together with the FB center and FC tail & (if desired) bellhousing. You have to swap over the 2nd gen extension housing to get the crossmember mount and shifter turret. Also, swap the 2nd gen speedo drive gear onto the output shaft. The bellhousing swap is optional - but the 12A housing is not vented, while the 13B is (extra heat in the clutch from the bigger motor). Make sure you re-seal ALL the seams between the cases on re-assembly or it will leak. Replace seals & gaskets, too. Use the FC switches (5th gear / neutral) so the plugs match your harness. Oh yeah, when you're re-installing the extension housing onto the center case, leave the switches out - it's easier to mate the pieces without them 'hanging up' on the control rod.

 

thanks man for all of this. so to sum it up is. i cant use my stock crappy fc tranny and a 12 fb tranny to make one good tranny? i have to have a gsl-se 13b tranny to make it work?

 

bumpity

 

hey slvr7 what about my slave cylinder and starter?? do those have to be replaced by 12a ones?

 

I *think* the FC starter and slave are fine with the 12A bellhousing, but I went with the FC bellhousing.
The 12A and 13B bellhousings have the same bolt pattern, either will bolt up to your motor.
The point I was trying to make, is that you have to use the FC extension/tail housing. To swap it onto the FB center section, you remove the long tension bolts holding the casing together. Once you remove them, you should split all the sections apart to reseal them, or it will leak. And so, if you have to pull off the bellhousing, might as well use the 13B version with the vented case. But you can start with a 12A or 13B FB tranny, doesn't matter.

 

alright man thanks. ill know how it goes in a few days

 

I put a 85 GslSE tran in my 83GS and it's perfect. 5th is noticeably taller.

B