Rotary Car Club - miata 5sp internals in fc 5sp

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miata 5sp internals in fc 5sp

I've read a couple of threads that say that they are a direct swap, is this true? Racing Beat says that the input shaft can be swaped(with the proper maching). Can you swap the internals from a miata trans in an fc trans? The reason I'm wondering is, my trans is grinding and I'm looking for an alternative to a rebuild. Thanks. Bryan

From rx7club.com and user RXgirl7

Quote:

for those of you who know me, i have been thinking about putting a miata transmission into my 89 GTU. i know this swap is common on race cars, but i have never heared of it being done on a daily driven car before(i serched, but i may have missed something). my car has a bone stock S5 motor(22k miles, running strong)and a stock exhaust system. i chose the miatabox because the gears are closer.
i picked up the transmission for $125, used from japan in excelent condition. no gears or synchros had to be replaced.
i decided to go with a racingbeat race pressure plate, and a racingbeat aluminium flywheel. i also installed a competition tranny mount at the same time. i am also running NEO synthetic 75w-90 in the new transmission. installation was done by John at Mazdatrix(thank you!)and the transmission was done by Brian Fields(thanks!)located right behind Mazdatrix.
in order to install the miatabox in an FC, the imput shaft has to be modified by a machinist, and the miata gears need to be inserted into an FC case.
the miata transmission has a very tall first gear, and it was assumed that driving the car on the street in stop and go traffic would be tricky. as soon as i drove the car around the block, all my apprehensions dissapeared. it is extreamly easy to drive the car, starts and hills feel about the same as they did with the stock setup. driving the car around town is a blast. it revs up quickly due to the flywheel, and i can ACCELERATE in 5th gear!
i took the car to Streets of Willow on saturday, and it was absoloutly a blast to drive. i have driven on that track before with my stock transmission, and the difference was quite noticable. 2nd and 3rd gear are much closer, and the car feels more spirited, zippy, and responsive than ever before.
top end in 5th gear is somewhat reduced(155mph @7500rpm)but 5th gear feels much stronger and more responsive. i would say it feels sort of like a 4th gear.
i had a Mazdatrix short shifter installed on my stock tranny, and it was quiet as a mouse. after we installed it on the new tranny, it rattles like a mofo, which has lead us to conclude that shifter rattle is specific to each transmission. more on this topic can be found on the Mazdatrix website.
everyone who has driven the car has given me positive feedback, and the car is an absoloute BLAST to drive. the results completly exceeded my expectations. in my opinion, there is absoloutly no downside to this swap. i would definatly reccomend this swap to almost anyone with an FC. the transmission has completly woken up my motor.

It has been my understanding that Miata 5spd internals are a direct swap into a FB/FC N/A trans case, other than the minor machining required for the input shaft.
Mazda Motorsports sells a custom gearset for both the Miata and RX7 trans. They list the input shafts seperately, but the rest of the gearset is the same for either application.

why not just buy another used transmission? i'm sure you would still come out cheaper.

In talking with Dave @ KDR, certain miata trans can be installed in the FC by simply swapping the bellhousings and sometimes modifiing the input shaft slightly. Give him a call, he may have the parts inhand to build you a trans and get it shipped right to you.

AFAIK it's any of the 5 speeds, but the 1.8 transmissions had better synchros than the 1.6 ones. The input shaft needs to be shortened.
http://www.mazdatrix.com/FAQ/MIATAINPUTSHAFT.HTM

Quote:

Originally Posted by TitaniumTT (Post 95978)

not sure how you swap the bellhousing on the smooth case transmissions.

Apparently it can be done with certain models. Otherwise its the internals that need to be swapped

I was looking at this, do you think that the Miata stuff will handle any drifting? or stupid driving for that matter? N/A transmissions are known for being a bit weak even in good condition, or so I heard...

It's not so much swapping bellhousings or anything like that, but more like swapping the Miata guts (contained in the center section), into an FC transmission case. The Miata gearbox is basically the same as the FC NA unit, I wouldn't expect it to be much, if any more durable. They are a known weak point on turbo Miatas (they're lighter, so can take more power to break them).

One trick to aid grinding synchros, which we have had quite a bit of success with, is to use a 50/50 mix of gear lube and ATF. The ATF has plenty of lube, but also has a butt load of detergents which really clean the synchros up and usually gets them working again. This might be worth a shot before seeking a new tranny...

.

ATF is way thinner, that doesn't seem like such a good idea. Redline MT-90 or MTL would probably be a better way to go. I use MT-90 and it's been good to me.

Don't use Royal Purple with an old tranny. The synthetic base that they use messes with the sync's.

Redline's doesn't. At least this is what I've experienced. Also, I wouldn't use ATF BECUASE of the cleaning properties it has. Instead I would use a 50/50 or 70/30 mix of tranny to 10W-30. I did this in my N/A trans during the winter months MANY moons ago when I was too cheap to sport for the Redline. Now it's redline in EVERY gearbox I own. It even cured the dreaded 2nd gear grind in my Aisin AX-15 in my Jeep despite how cold it gets in the winter.

i always remember my jetta i had grinding like crazy in the winter time...Rx7 never has really.

Then again i have issues with reverse just not working. Impossible to get into. Not sure what that is about.

No reverse sync? Every so often my truck will do that and I'll have to put it into neutral, engage then release the clutch to spin the gears and it usually goes right in.

On a different note - my new 6-spd tranny got here today. Something to think about. If a company can get away with building a transmission in three sections, then mixing and matching sections to fit it into an exponential amount of cars, why wouldn't they? Example. Changing a bellhousing allows it to mount to different engines, changing a tailshaft allows different lengths. The bulk of the internal parts are all the same so it makes sense that interchangabilty would be pretty strait forward. Jeep guys have been doing it for a LONG time.