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PostPosted: October 11, 2010, 2:35 am 
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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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PostPosted: October 11, 2010, 5:21 pm 
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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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PostPosted: October 11, 2010, 6:25 pm 
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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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PostPosted: October 11, 2010, 10:50 pm 
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chetcpo wrote:
This 6 spd. isn't the maita transmission that bolts up to the 2.0 Duratec is it?

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 :wink:

Moti

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PostPosted: October 12, 2010, 6:27 am 
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chetcpo wrote:
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?

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
Image

Bill


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PostPosted: October 16, 2010, 1:10 am 
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Blackbird wrote:
chetcpo wrote:
This 6 spd. isn't the maita transmission that bolts up to the 2.0 Duratec is it?

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.

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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PostPosted: November 5, 2019, 4:20 pm 
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Quote:
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.


Does anyone know whether the NC 6-speed transmission is dimensionally similar to the 5-speed and NB 6-speed transmissions? In particular, is engine/bellhousing bolt pattern identical?


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PostPosted: November 7, 2019, 11:10 am 
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NB and NC do not share a bellhousing pattern. If you have a Mazda MZR or Ford Duratec engine, you want the NC 5 or 6 speed. If you have a Mazda BP engine, you want the NB 5 or 6 speed.

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PostPosted: November 7, 2019, 2:15 pm 
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Quote:
NB and NC do not share a bellhousing pattern. If you have a Mazda MZR or Ford Duratec engine, you want the NC 5 or 6 speed. If you have a Mazda BP engine, you want the NB 5 or 6 speed.


Thanks! I'm planning to use a Vitesse adapter to pair a Miata transmission to a 1.6l Ford Ecoboost engine (same block as the Sigma / Zetec SE). I was under the impression that all of the Miata transmissions were backwards/forwards compatible relative to bellhousing bolt patterns, but apparently not. So I've asked Vitesse to clarify whether their adapter is configured for the NB or NC series transmission.

The NB and NC series 6-speed gear ratios are somewhat different, but I think either will work for my application (not a Miata), and both are readily available.


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PostPosted: November 7, 2019, 4:59 pm 
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Additional question. . .

My understanding is that the Miata transmission doesn't use a conventional cross-member for mounting. Are there any plug-and-play solutions for converting a Miata transmission to a cross-member type mounting scheme? I seem to recall the RX7 Turbo 2 transmission mounts using a conventional cross-member, but it seems unlikely the parts would transfer to the Miata transmission.


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PostPosted: November 7, 2019, 10:41 pm 
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The 1995 5-sp trans has 2 threaded 10 mm threaded holes on the underside of the tail section (other year models should be similar) which work well to attach to a cross-member mount. Some adjustments may be required to adapt an off the shelf mount. On the other hand, a cross-member mount is not that difficult to fab.


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PostPosted: November 8, 2019, 12:15 am 
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waltj wrote:
The 1995 5-sp trans has 2 threaded 10 mm threaded holes on the underside of the tail section (other year models should be similar) which work well to attach to a cross-member mount.


Thanks for the info. Unfortunately, the 5-speed torque/power capacity is probably a little marginal for my application (>220hp, >210ft*lbs). Does the 6-speed have a similar feature that lends itself to conventional cross-member mounting?


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PostPosted: November 8, 2019, 4:39 am 
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The Miata 6 speed transmission has a large boss on the right side of the tranny where the front of the torque beam fastens. The photos below shows this feature. This can be used to design a cross member mount for the rear of the tranny. These photos show three examples of rear tranny mounts used with Miata drive train Locosts.


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PostPosted: November 8, 2019, 4:38 pm 
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Thanks! Super helpful.

Rear cross-members aren't particularly hard to fabricate, and that boss looks plenty stout enough to act as a mounting point.

I need to take some measurements this weekend to verify the Miata transmission will work relative to shifter location. I hope so because it is by far the best bang for the buck. If it won't work, I might have to bite the bullet and buy a custom QuickTime bellhousing to accommodate a Tremec TKO.


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