The Miata 6 Speed Transmission into an FB Thread...
 

I guess the title of the other thread is fooling folks, so I'm starting this one. Here's the lead up...

As can be seen, everyone is all about the 5 speed swap. Here's where I left off in that other thread which is slowly sinking to oblivion...:p:

I used "Miata transmission swap" as keywords in the archives, FAQ thread and in this 1stgen section and only six threads popped up. Of those, this is the ONLY thread (that was the old thread...) with a clear reference to what I'm contemplating now that I've power-shifted my '83 GSL tranny to death.

Does anyone have the answer? The linked sites talk about pre-'99 Miata 5 speeds, but ignores the 6 speed citing its ratios only as reference.

:cool:

I say go for it!! A stock FB always feels like it needs one more gear for the highway cruising.

there are 3 different 6 speeds, from mazda.

1. the 99-05 miata 6 speed. it has the NA input and output shafts, and is designed to interchange exactly with the miata 5 speed, and it does, except for 1 starter bolt.

2. the 04-now rx8 transmission. its got the all important rotary bellhousing, but it uses the turbo sized flywheel/clutch/output shaft. there is also no speedo gear, as the rx8 uses the abs sensors.

3. the 06+ miata 6 speed; its based off of the 5 speed truck transmission in the ford pickups...

so, the rx8 trans will bolt right up to the engine, using a turbo clutch and flywheel, but you need a turbo drive shaft too, but theres no speedo gear, so you're on your own there

the miata trans will use the na clutch and stock driveshaft, but it wont bolt to the engine. it does look like the rx8 bellhousing will swap on to the miata trans, but then you'd still need the turbo clutch.

The Ford truck transmission, known as the "Kogyo" (Toyo Kogyo = Mazda), has its roots in the old "Ribcase" unit, which was what the Turbo trans was based on.

Woah. That's about as cool as the "NSU designs an engine for Mercedesm but instead it gets appropriated by VW, from where it gets cribbed and biggiesized by Dodge, who are bought by Mercedes, but not before an update of that engine is used in the Mini which is owned by BMW, who were the reason Mercedes wanted a new engine in the late 60's in the first place" story.

Same basic engine used by VW since 1975 to the present, the basis for engines used in BMW and Mercedes products, was originally designed by NSU, who were responsible for some other weirdball engine designs... :D :D

Back to lurking.

1. the 99-05 miata 6 speed. it has the NA input and output shafts, and is designed to interchange exactly with the miata 5 speed, and it does, except for 1 starter bolt.

Will the input shaft from the six speed fit into the stock '83 clutch assembly? I know the shaft is longer, but if a plate is made that could allow for a bolt on situation, that difference (approx 1" or so?) would make an adaptor plate scenario much easier. Inside, a custom middle dash area would have to be made for a shifter that much further back, but that is not a problem either.

It's a matter of the spline and pilot still being "FB" sized. What is the spline count and size of the FB input shaft?

So far, the cheapest '99 6-speed Miata transmission is $850...but that is shipped to my door. No telling what one would cost if I legged it myself over to Mazda Heaven in Kennedale.

:cool:

I *think* the FB input shaft is 15/16 & 22 spline.

the 6 speed miata transmission is of totally different design.
The Miata 5 speeds can be swapped with the RX7 NA 5 speeds becuase they share the same gear box designs. To swap between the 2, you do some changes to the input shaft(length issue) and swap out the bell and tailshaft housings between the two.
The miata 5spd and 6spd swap between eachother when applied to the miata engine becuase they have similar bell housings.
I have no idea how the rx8 6spd trans is put together so I have no idea if they would do bell housing swaps with the miata 6spd. As is though, the rx8 gear ratios dont look very appetizing

+1, From all the info that I've gathered.

To put Miata gears into the FB, you'll need your FB tranny as a donor for housings and to grind off some of the input shaft. I have a whole thread on the stuff. Lemmie find out.

First, some links for anyone else interested:
All the gear ratios ANYONE would ever need: http://mrmazda.no-ip.com/tranchrt.txt
5th gear interchange chart: http://members.aol.com/solomiata/Mi...nterchange.html
SoloMiata drivetrain interchange guide: http://members.aol.com/solomiata/Drivetrain.html
Regearing Mazda transmissions: http://www.angelfire.com/darkside/d...ansmission.html
Miata VS RX-7 input shaft comparison: http://myweb.cableone.net/currie/tom/RX7/trans.html

These were done for my research into putting a Miata 5 speed into an FB.

I also have the same info in the FC section here:
https://www.rx7club.com/2nd-generation-specific-1986-1992-17/miata-transmission-into-na-fc-results-481920/

There have also been a few threads in the first gen section...

In order to bolt the Miata tranny to the rotary, you'll need the rotary bellhousing. Unfortunately on N/A trannies, the bellhousing and part of the rest of the tranny casing are one unit, hence you have to swap most of the case to get the belhousing. This kinda makes the 6 speed swap impossible without a custom adapter plate.

If the 5 and 6 speed boxes swap out in Miataland, then it stands to reason that the input shafts are of comparable length and of the same spline pattern and diameter. Though I can't confirm that they do indeed swap out. I haven't gone as far into the 6 speed swap to see what the spline and diameter pattern is of the input shafts and clutch discs. The idea of fabbing up custom mounts and an adapter plate kinda turned me off, as I like to use parts that I can easily find should I break anything... If I ever get a CNC milling machine or perhaps a knee mill wiht digital read outs that may change.

The 5 speed swap is more popular because it's easier to find Miata 5 speed trannies and the guts swap out with RX-7 trannies so mounting is easier.

I believe the 6 speed is made by AISIN...

According to one of your links, you're absolutely right. The link for the "Regearing mazda transmissions" tip is dead now, BTW.

Looking at the input shaft side by side shot makes me think the whole 6 speed swap could be a bolt-on affair with only four things.

• An adaptor plate.
• A reworked crossmember.
• A custom center console.
• A custom driveshaft

The big sticking point is the spline count. Both of the shafts are 15/16" in diameter, so the 6 speed input shaft will pop right into the '83 clutch assembly as long as the spline count is the same. It looks like the tip of the Miata shaft might have to be cut down, though, to match the spline-to-tip measurements of the FB shaft.

If I can find one of the trannies under $500, it's worth it to me to try the swap, but so far the cheapest one is that $850 one. A sweep through the Kennedale salvage yards today came up with no 6 speed transmissions and the sad observation that 1stgen RX-7s are now starting to become a rarity in my favorite hunting spots.:(

:cool:

Fuckin' A... The dots got copied rather than the full URL and didn't translate into the URL tag well.


Actual links:

5th gear interchange chart: http://members.aol.com/solomiata/Mia...terchange.html
Regearing Mazda Transmissions: http://www.angelfire.com/darkside/de...nsmission.html

Alternative for tranny regearing:
http://www.mazdatruckin.com/B2200/Transmission.html
And page 2:
http://www.mazdatruckin.com/B2200/Transmission2.html

With tranny selection guidelines that are redundant to the previous links:
http://www.mazdatruckin.com/TrannyInfo.html

lol...you Mazda truck guys are hard core and messed up...:rlaugh:

:cool:

The Miata 5 speed has the 15/16" input shaft and I found that it has a 22 spline count. Since the Aisin AZ6 transmission is supposed to be a bolt in affair for the 1999 Miata, is it safe to assume that the input shaft has the same specs? I googled the hell out of this and I can't get any hard dimension or specification info for the AZ6.:mad:

To the other question...what is the spline count for the 1983 RX-7 clutch assembly? We know the FB transmission also has a 15/16" diameter shaft, but I have no desire to do any more searching tonight on this problem. It's time for dinner, so I'm hoping some hardcore rotarynisti can help me out with that piece of information.:D

:cool:

:wallbash: I got this info from a parts store website. Accuracy cannot be conformed :wallbash:

I recently bought new Tilton clutch discs, they are 1" x 22 spline
Fits like a glove.(not OJ's glove ofcourse)

https://www.rx7club.com/showthread.p...ghlight=spline

The change to the 1" shaft was for turbo cars, I believe, and then across the board at some late '80s year...with a 13B PP, I imagine you're not running a 215mm disk, but then again.....

Rogue_Wulff----> Can you please use that same reference source to find out the specs for a 1999 Mazda Miata MX-5 10th Anniversary Edition 6 speed transmission input shaft? Size and spline count again, please...:)...this would be the Aisin AZ6 6 speed transmission. This is starting to look like it could be feasible even if it means going a little deeper into credit card debt...:p:

:cool:

99 Miata shows to use a 7/8 x 22 spline clutch disc. (didn't specify 5 or 6 speed, must be the same clutch) Also says it's a 215mm disc. Simple fix, miata disc, RX7 pressure plate, if the miata one wont fit.......
Ok, so the 83-88 RX7 uses a 225mm (8 7/8") disc, while the 82 and older had a 215mm (8.5"). Smaller disc can be used without a problem. Or, get a custom setup from a rebuilder.

Oh no.....it says 7/8" as opposed to 15/16"? That sixteenth would seem to be a significant difference when it comes to the drivetrain and the transfer of torque...:(

:cool:

so as I gathered....in order to fit a miata 6 speed into a FB, you'll need to bring your FB transmission, the 6 speed straight to a tranny shop. There they can swap out the casings and input shafts.

It sounds WAY to complicated to avoid the tranny shop..trying to frankenstein a miata 6 speed, 5 speed, and your FB tranny if not just the rx8 tranny..

I have no experience with the 6 speed but the 5speed's or early miata's bell housing has different bolt pattern; therefore it wont fit. However, we did a transplant on a 1st gen tranny housing and shortened the input shaft. Btw, this tranny was in my bro's RX-2.

No. 6 speeds are a completely different animal. Nothing is interchangeable between the 6-speeds and the 5-speeds.

There is a fair amount of swappability between Miata 5-speeds and N/A RX-7 5-speeds, and between Miata 6-speeds and RX-8 6-speeds. That is where you see people putting Miata *5 speed* units in RX-7s, since they have much nicer gear ratios. They're still not ideal, but Mazda never made a 2:1 1st, 1:1 5th transmission....

Which reminds me. I need to bitch-out Directfreak again for wanting a taller fifth gear. Nothing at all wrong with spinning 5,000 down the highway...

No need to. I resolved it by putting a 3.73 rear gear in. Highway crusing is nice now,
and third gear will go up to 110mph (at redline).

yeah, you suck, DF. :) you and your blasted high HP turbo forcing you to get that Ford rear, right? and i would imagine a pretty healthy choice of ratios to boot, too, eh? if you know of somewhere with a similar ratio for the stock GSL/GSL-SE rears, please spill - post or PM, whichever. all i've every seen are shorter gears. :(

Let's see you pass uphill in 5th gear... :)

Okay. Gotta find the video that Tranquil took and digitize it so I can throw it on YouTube...

I got them also from the old school RX-3's...My inventory ranges from 3.73, 3.90, 4.10, 4.44, 4.78 and 4.88. You can get the small gears from early RWD GLC's and 626's.