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So I finally got around today to put the 5 speed miata trans next to the 6 speed, side by side.
There are some clear differences in dimensions but the most important thing it that they are interchangeable - at least on miatas.
Engine to bell housing bolt pattern is similar and so are the overall length, input / output shafts, shifter location and PPF mounting points.
They use the same clutch, slave cyl, throwout bearing etc...
The starter and shifter are unique to the 6 speed.
You can bolt a starter off a 5 speed car to the 6 speed trans using only 2 out of 3 bolts.

On a locost, if you're building with a 5 speed and you think that you may upgrade to a 6 speed in the future, you'll need to make sure to leave enough space.

The dimensions are approximate, not a blue print - just something to give one an idea.

HTH,

Moti

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Moti

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Thanks for the post Moti, that's good to know it can swap. This 6 spd. isn't the maita transmission that bolts up to the 2.0 Duratec is it?

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Thanks Moti!

In the probably useless suggestions dept., you could unbolt the bell housing from the 6 speed and connect it to the IRS diff. Then on a BEC you would get a reverse and 6 different overdrives to calm down the engine.

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Negative on that, this is the trans that first showed up in the 99 10th AE and then through 2005 in various packages (sport, LS, Mazdaspeed) and special editions.
It is possible the the mid case is shared with the early 6 speed transmissions of the NC, I have not verified it yet, however, in the later NC generation the trans was replaced with a brand new 6 speed model.
the easiest way to tell is by the location of reverse on the shifter - the NB / early NC trans is down all the way to the right while the newer NC is left and up.

BTW I suspect that the change was parallel to the RX8 which had the update to a new 6 speed as well right about the same time, it is likely that short of the bellhousing things are interchangeable.
The bellhousing is definitely different.

Marcus, I guess this could be done with Lots of quality time in a machine shop.
I bet it'll be easier to just put a transaxle in the back and be done

Moti

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It is very easy to I.D. a Duratec transmission. The bell housing bolt pattern is a perfect circle. At least to my eyeballs.

Here is shot of the Duratec pattern


Bill

After having a couple 2006 Miatas (NC) on the rack in the shop in the last couple of days I can assure you that there is nothing in common between the NB 6 speed and the NC 6 speed - they are completely different animals.
The NC always came with a 6 speed trans that had reverse on the top left corner on the shifter.

However, I also had a couple of RX8s on the rack this week, one was a 04 and one was 08.
The RX8 did have the 6 speed trans changed during the production run.
The 04 RX8 6 speed has a similar mid-case to the NB and it is likely that parts can be swapped between the early production RX8 6 speed and the NB 6 speed.
The late production is similar to the NC trans, so things should be interchangeable between these two to some extent as well.

Moti

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