A possible Australian option for a stronger 6 speed

[ManiacLachy]

I'm taking this conversation from MiataTurbo and bringing it here, but see the original post if you haven't yet.
https://www.miataturbo.net/suspension-brakes-drivetrain-49/500nm-torque-nb-6-speed-transmission-105065/

The topic discusses something near and dear to the heart of anyone wanting to push their power level, the strength of the gearbox! A known issue with the NB 6 speed is that in high torque applications (~300ft/lbs is what I hear thrown about), 4th gear breaks! Options to avoid this are a replacement gearbox, such as the BMW boxes, or T5s, but they get expensive fast, and alter the ratios, and basically open up a whole new can of worms.

The MT thread discusses a possible fix as performed on other versions of our 6 speed found in other cars, but describe the same issue. So the solution could likely work for us too! And the best part is, Neat Gearboxes who do the fix are Australian!

https://neatgearboxes.wordpress.com/2014/04/16/nissan-silvia-s15-6-speed-gearbox-circlip-mod/
http://www.neatgearboxes.com.au/

I note the blog was written in 2014, and I'm not sure why its flown under our radar for so long, they even mention the MX-5 as a shared gearbox platform. It might be worth investigating further at least.

[The American]

It’s definitely something to look at. I’ve been quoted about $900 plus parts to assemble a six speed, and if you add this to the mix it gets close to 2k for a rebuild that fixes only that specific weakness. If you have an unbroken 6speed (~$1200 value) which you could sell, the ‘comparable cost solution kitty’ gets close to $3k.

I can see why people would rather spend that much to switch to either a stronger overall gearbox or at least a solution that allows them to be more cheaply consumed (T5 for example).

The PAR gearset includes the same/similar fix for 4th.

For a medium duty solution, the Neat GB arrangement could be a good way to go for some peace of mind.

[greenMachine]

I saw that thread, but didn't twig the local connection.

There is another thread which discusses this failure mode. It suggests a tack weld or two to prevent movement . In that thread someone questions the need for the mod, as Mazda (Aisan I guess) modded the box sometime over the 98-05 production run to better retain the bits in question.

I agree, not cheap, but 6-speeds are getting scarcer/more expensive, and by the time you replace a box a couple of times the cost and effort would have to be worth putting out for the mod in the first one.

The other issue is the extent of parts interchangeability, that should help keep confidence in the box, as long as you can salvage your front case from the wreckage ...

Of course, this just means that the HP/TQ limit has been pushed up to 500nms, crank up the boost and use it all bro

[project.r.racing]

Plenty of RX8s and 86s in wreckers. While this isnt a new concept. Maybe the lack of modified NAs and NBs in the past decade has made the info redundent.

[ManiacLachy]

Seems someone reached out to Neat and they have done a few MX-5s locally.
https://www.miataturbo.net/suspension-brakes-drivetrain-49/500nm-torque-nb-6-speed-transmission-105065/#post1598196

Confirmed! They are the same gearboxes. I have sent an email to the guys at Neat Gearboxes and they have confirmed that the modification can be made in the 6-speed transmissions because the counter shaft is exactly the same as in the Nissan Silvia S15, Z33, Lexus, Toyota etc. I reproduce the answer below:

Hi Ramos,
Yes, the clip modification works for the Miata / MX5 6-speed transmission, we have done at least 5 or 6 Miatas.
While I don’t have any lab testing or anything, we do have over 60 of these in the real world being used since 2015. I have seen one break in a BRZ with 303kw@wheels. And in fact, it was not the clip that broke but 4th gear itself. Other than that, I don’t think I’ve heard of any breaking with our modification.
I have a Lexus IS200 with a turbo charged BEAMS motor. it is on run-in tune but will be easily capable of 300wkw. I have done the C-clip modification to that gearbox too, so it will be a good test.
The difficulty is that the shafts must be sent to us in order to machine them correctly to suit our larger, stronger C-clips. It does make logistics a little harder and more expensive.

Kind regards,
Sam Charlick
Owner/manager
Neat Gearboxes

It is a really economical option compared to other solutions such as Kmiata and its conversion kit to BMW transmission.

As poject.r.racing is saying, I think until recently there really weren't too many high HP MX-5s and not locally. Remember when Charlie hit 300whp, that was a big deal! Now 300whp is pretty easy with modern turbos, E85 and the current aftermarket ECUs. I feel like when Neat discovered this issue we weren't really knocking on the door of 6-speed failures like we are now, so the information fell into a blind spot.

For a medium duty solution, the Neat GB arrangement could be a good way to go for some peace of mind.

This describes me, and others like me (aka Lokiel). I want peace of mind to one day run my EFR6258 at full tilt on 98 (maybe E85), but mostly on the street. This gearbox with a re-enforced diff housing should see me satisfied, and for far less than a K-Miata BMW solution and Getrag diff, and all the issues that brings (paging Daffy, paging The Problem Child ). But I think for your use-case, it might not be enough. You'll abuse it far harder than I ever will.

[greenMachine]

He is saying essentially that it is good up to 300RWKw, not 300rwhp, that's 400rwhp. OK one broke at just over that, but it sounds like he is going to torture-test at around 300RWKw on his own car, which suggests he thinks it will hold at that level.

That's a LOT of grunt. It is what, 60RWkw above the nominal limit for a stock 6-speed, a useful boost for those for whom 240 is simply not enough ...

[Lokiel]

Definitely interested in this but wary of throwing money at what is a shitty gearbox to start with.

I've got the MR tall-angled SSK which helps prevent missed gear shifts and allows me to find reverse every time but it's not even close to how a good 5-speeed gearbox feels.
My 1982 Mitsubishi JA Starion's gearbox was flawless (other than being geared wrong for a steady 60km/h, 3rd was too high and 4th was too low so I
drove it at 70km/h in 4th in 60 zones).
I love the NA's 5-speed gearbox.
I even like my 2x Mazda 3 5-speeds (one of the reasons I chose the older BK both times over the BL for a DD).

Depending on cost, I'd likely pay double for a BMW 6-speed conversion and get a gearbox that I love.

If we could organise a "Group Buy" deal, I'd consider it more (everyone loves a deal).

[ManiacLachy]

I only had a brief and sedate drive in Daffy's car, but I really didn't like the feel of the BMW 'box, which is another reason I'm not very interested in going down that path. I would love another go for re-evaluation, with maybe a little more driving aggression, Tony's been threatening to visit me for nearly a year now but he's yet to darken my driveway

I've read too many stories of rabbit hole like issues with the BMW conversions, a long list of find and fix issues. If it was just the cost of parts and labour for an excellent shifter, that handles all the power you could reasonably expect, and just worked - then yeah great, I'd bite the bullet and get it done. But that's not what I'm hearing.

I'd rather keep the ratio and shifter I know, just with a higher capacity. I certainly don't think the 6 speed is a bad shifting gearbox, and I actually prefer my SE's with the MR kit to the 5-speed I had in the NA.

[Lokiel]

Some Aisin 6-speeds are worse than others bit you must have a bloody good one to consider it better than an NA's 5-speed (or a really crappy 5-speed).
I'm hearing you though on going down a potential rabbit-hole with the bmw gearbox and would want to test-drive one before pursuing that option.

[greenMachine]

I've read too many stories of rabbit hole like issues with the BMW conversions, a long list of find and fix issues. If it was just the cost of parts and labour for an excellent shifter, that handles all the power you could reasonably expect, and just worked - then yeah great, I'd bite the bullet and get it done. But that's not what I'm hearing.

Where are you reading this? MT.net? I read that regularly, but don't recall anything along those lines but perhaps I am not looking in the right place.

I'd rather keep the ratio and shifter I know, just with a higher capacity. I certainly don't think the 6 speed is a bad shifting gearbox, and I actually prefer my SE's with the MR kit to the 5-speed I had in the NA.

I am not unhappy with my 6-speed+MR tall angled, but it seems like a long time ago that I drove a 5-speeder. Regardless, I can't claim to have great memories of my 5-speeder.

[ManiacLachy]

Where are you reading this? MT.net? I read that regularly, but don't recall anything along those lines but perhaps I am not looking in the right place.

I'm probably reading a little too much into it and extrapolating from only a couple of cases now that you mention it. The 2 that stick in my mind are Greg Peters (carpassionchannel) and Daffy. Maybe most people have no issues? But I haven't read any stories saying celebrating it either. I just have a feeling its a bit Emperor's New Clothes I could be completely wrong of course.

I really wish I got the tall angled instead of stock height MR SSK.

[Lokiel]

:
I really wish I got the tall angled instead of stock height MR SSK.

Buy it, sell the stock-height MR SSK to cover some of the cost and both you and the buyer are better off!

[RS2000]

I straightened the angle on my MR tall angled by about 50%, because I couldn't get used to the knob being that far off centre.
Also, of course, the longer the lever the less of a short shifter it becomes.