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NA vs. NB Transmissions

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#1
bmarshall1

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Time for my monthly "This is probably a stupid question but I don't know the answer";  I have always thought that NB transmissions were stronger than the NA - maybe just the housing due to the additional webbing on the exterior.

 

My friend recently bought a trans for his 99 from the race shop and they sold him an NA stating it's basically the same but shifts smoother.

 

Any information anyone can share regarding the NA vs NB?



#2
Ron Alan

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"Strength" I believe may not be an accurate term. I think over time certain minor aspects were changed at the original source to improve functionality and eliminate certain things from happening(reverse at speed?). But I do not think the actual gears and main shaft have changed? And when a "rebuilder" has the unit apart they are changing wear items...Syncros, syncro springs, shift forks, roll pins, all seals, etc. All gears and probably shift hubs remain? The time and expense to replace all isn't practical. 

 

All that said...I think we are definitely beginning to reach life expectancy of 3rd gear which seems to blow up/fail at the highest rate. One of our local guys will replace 3rd gear for an additional rebuild cost but apparently Mazda is not able to keep stock of these. He said he bought every piece Mazda had awhile back and hasn't been able to get more(this was a conversation 2 months ago). I had 10 junkyard trannies 1 year ago and have none now. Getting harder to find easily. I wont hesitate to use either NA or NB. In the end It is a crap shoot on its life expectancy...and if you are a shitty shifter and running a Unsprung clutch disc good luck. Jim has always advocated a stock PP as well I believe. Eliminating the "shock" on these units is always a good thing!

 

I will gladly be corrected if anything here is not accurate...always learning!

 

For those trying to diagnose problems...if you suddenly begin missing shifts and/or grinding...check the easy things 1st! Pull the shifter and make sure the plastic bushing on the ball hasn't broken...also make sure your clutch slave cylinder has a good throw...barely disengaging the clutch will make it harder to shift(maybe air in line?)


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#3
LarryKing

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Better call Saul.

 

I've always heard that NA and NB are essentially the same and that the NB supersedes the NA part no. I think I read that new gearboxes from Mazda are on back order.

 

My understanding is that the synchro snap rings are the weak link. Gearbox guru Mark Bennett first diagnosed this issue and had hardened snap rings manufactured to use in his "blueprinted" Miata transmissions. I believe Planet Miata and East Street subcontracted this technique (I may be wrong about that).


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#4
bmarshall1

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Good points All.  maybe 'better' or 'reliable' is a better descriptor.  I have heard of the minor changes throughout the years as well as the snap ring issue.  I am pretty easy on shifts, on the other hand my race buddy does not rev match and will go through one every few years (at 4 races a year).  

 

Good to know NA or NB will get the job done.



#5
Steve Scheifler

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Don’t take this as verified fact, but I believe there are one or more internal parts no longe available for the NA transmission, but those and certain related parts can be replaced together as a set. Sorry to be so vague but the point is that if certain parts need replacing in an NA box the rebuild will be more expensive than the same issue in the NB. Hopefully someone can supply the details.
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#6
EMatoy

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This link below should answer some of your questions from 1.6 to 1.8 NA transmissions. Then from NA to NB there are more changes. A few are: NB shifter has 2 pins to locate it in the shift turret, NA has one. I do believe the synco setup from NA8 to NB is the same (NA6 had a single cone synchro for 2nd, later parts had a dual cone). Shafts are the same, gear size in 1.8 to NB is the same.

You can interchange single cone to dual cone parts but if swapping a single cone synchro to a double you have to swap the gear and synchro together.

I have had good luck with all generations of transmissions. It’s all in how you shift and the clutch disk of choice.

https://walter-motor...ion-differences
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