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Transmission replacement in an ITA Miata (1.6l)

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#1
riderosa

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Hello,

 

I have been racing an  ITA Miata.  The tranny is not shifting correctly in 5th or reverse (sometimes not at all).  Since I bought the car used and don't know how many miles are on the tranny, what would you recommend I do?  Is there a transmission more reliable that would fit say from a 99 Miata? Does  Improved Touring allow that?

 

Rich

 



#2
Jeff Wasilko

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Improved Touring doesn't have a VIN rule, and transmissions are interchangeable from all NA and NB.

 

5th/reverse failure is a common failure.



#3
riderosa

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Is there a preferred year(s) for improved reliability/robustness



#4
FTodaro

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People like the NB transmissions, it has a different and improved shifter, and a better interlock mechanism, as well as an better second gear design.

Your problem on your current trans is likely the syncros, if it shifts fine when the moter is not running.

It is a good practice to go through the box once a year if you are hard on transmission and every 2 or three years if you are gentle.

Frank
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#5
riderosa

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If I change over to the NB transmission what else is needed to use in the NA Miata. Just a new shifter?



#6
Bench Racer

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Part of the improvement of the NB transmission is the shift lever has two pins pressed in the aluminum housing and two slots in the ball on the shifter lever. If by chance you can't find a NB shift lever you can press one of the pins in the aluminum housing out of the way and use the NA shifter. It might be a good idea to replace the parts/bushings that the shift lever moves about in. Half way through this video the replacement parts are talked about.

https://www.bing.com...FC&FORM=VRDGAR 


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#7
FTodaro

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If I change over to the NB transmission what else is needed to use in the NA Miata. Just a new shifter?

Yes all you would need is an NB shifter, there are lots of used ones out there laying around. Otherwise the case is the same, the connections for the rev lights may be different but you can keep your old sensors and swap them over to the new transmission, the locations are a little different but they will plug right in and your good to go.


Frank
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#8
Jim Creighton

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Are the gear ratios the same for a 1.6 and a NB?  Also, just curious as to whether you can upgrade the rear end from a 1.6 to a 1.8 in ITA. I remember sometime last year at one race in SEDiv all the ITA Miatas had to waive points at one race for something. Anyone remember the reason/specifics? No dog in hunt, just curious.



#9
FTodaro

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Are the gear ratios the same for a 1.6 and a NB?  Also, just curious as to whether you can upgrade the rear end from a 1.6 to a 1.8 in ITA. I remember sometime last year at one race in SEDiv all the ITA Miatas had to waive points at one race for something. Anyone remember the reason/specifics? No dog in hunt, just curious.

The transmission gear ratio's for a standard 5 speed are the same for all years, the diff's can be different, In SM you can upgrade the diff's to torsen and cusco(for NA16)  but the 4/11 ratio has to be maintained. Cannot comment  on the ITA issue.


Frank
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#10
steveracer

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4:30 gear ratio


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#11
Bench Racer

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 Also, just curious as to whether you can upgrade the rear end from a 1.6 to a 1.8 in ITA. I remember sometime last year at one race in SEDiv all the ITA Miatas had to waive points at one race for something.  No dog in hunt, just curious.

Presume stock means, OEM diff. which came in specific car. 1.6 has a 6 inch ring and pinion and the 1.8 has a 7 inch ring and pinion. The diff. housings are different.

 

4. Transmission/Final Drive

a. Any final drive ratio is permitted provided it fits the stock differential/transaxle housing without modification to the housing.

b. Any limited-slip or locked differential is permitted. In AWD cars, the center differential must remain stock.

c. No alteration to the stock transmission gear ratios for the make, model, type and engine size of automobile is allowed.

d. Hardware items (nuts, bolts, etc.) may be replaced by similar items performing the same fastening function(s).

e. Shift lever may be bent or cut above tunnel or floor. The use of a Short Shift Kit is permitted. f. Traction control, if available, must be disabled by disconnecting or removing a minimum of three wheel speed sensors.


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#12
callumhay

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Are the gear ratios the same for a 1.6 and a NB?  Also, just curious as to whether you can upgrade the rear end from a 1.6 to a 1.8 in ITA. I remember sometime last year at one race in SEDiv all the ITA Miatas had to waive points at one race for something. Anyone remember the reason/specifics? No dog in hunt, just curious.

Was that the Daytona race with the NB spec miatas having to waive points for ITS? Due to power steering delete and now racing STL instead?

 

I guess the fastest 1.6's look at the mazdaspeed or cusco diff? I even heard welding the VLSD? Flame on if I'm incorrect but just repeating what I have heard,,,so you know how that goes. I guess a hard core ITA 1.6er could look at changing different diffs and diff ratios for different tracks...as if there wasn't enough work already for that $5 plastic trophy.!



#13
FTodaro

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4:30 gear ratio

whoops

That is correct not 4:11


Frank
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#14
joe varble

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 What Bench said,



#15
SaulSpeedwell

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Was that the Daytona race with the NB spec miatas having to waive points for ITS? Due to power steering delete and now racing STL instead?

 

I guess the fastest 1.6's look at the mazdaspeed or cusco diff? I even heard welding the VLSD? Flame on if I'm incorrect but just repeating what I have heard,,,so you know how that goes. I guess a hard core ITA 1.6er could look at changing different diffs and diff ratios for different tracks...as if there wasn't enough work already for that $5 plastic trophy.!

 

Welding an open or VLSD is not a great option, although it is cheaper/faster than a pure open unit.

 

The MazdaComp was a pretty great LSD despite being only available as a 2-way diff and with no tuning options offered other than "rebuild kits" (long since NLA), but 80% of the ones I see these days are approaching the end of their useful life.  They can be refurbished, but we are having to remachine the cases. If you can find a good one with a gentleman's warranty for <$600 for the LSD itself, it is still a good deal, in my mind.

 

I think the Cusco is the best bang for the buck of the aftermarket Miata options, primarily because it comes configurable 2 of 3 ways versus the pricier "Cadillac" OS Giken unit, and because (thanks to Spec Miata) there are many more Cuscos being used than OSGs, when it comes to low-powered, over-tired, 11/10ths-driven Miatas.  How KAAZ sells their near-Harbor-Freight-quality minimum-parts-count unit with a straight face for only a ~$100 discount, I have no idea.  What I will say now that I didn't say in the video below is that the KAAZ housing is STEEL, not aluminum, and it appears to be bare steel with no treatment at all, which is probably why it came straight out of the KAAZ box with orange pebbly rust in the crevices of the case internals.  

 

There are enough Cuscos in the field that we are starting to get real confidence in how to set them up from SM to STL+ power levels.  It would be great to have a massive A-B-A test of Cuscos and Gikens, but in the meantime, we have a lot more real-world data on setting up the Cusco. I'm not a dealer or distributor for any of the aftermarket LSDs, and have no relationship with any of those manufacturers, for what it is worth.

 

The worst thing about the 1.6 differential is that the 6" ring and pinion are anything but bulletproof.  If they are set up for max durability, properly cared/fed on fluid changes, and inspected/readjusted every "X" hours, they can still last long enough to not outpace your tires/brakes/transmission/engine refresh/steak/margarita/tow vehicle maintenance/front hub budget. :) :) :)

 

I make some mistakes in the narrative here, so read the video description if you are interested in KAAZ/Cusco/Giken stuff.


 


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#16
callumhay

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Thanks Mark, really helpful information

#17
luvin_the_rings

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which transmission is lighter? NA or NB? 



#18
FTodaro

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which transmission is lighter? NA or NB? 

I have never weighed them but they are virtually identical the only difference for the most part is the tail shaft assembly (shifter housing) . what ever the weight difference it would not show up in any data.


Frank
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