Gearbox woes...looking for advise & suggestions from the brains trust
 

Now that I have finally fallen in to the INTENSE peer pressure of "MiataTurbo.net - 1800 or u suck" crowd......first race meeting....Gearbox failed race 1 lap 2.

So screw you guys i'm going home!

:)

Jokes aside, pretty bummed to have it fail with a purposely lower tune for that very reason....273 ft lbs and only 293 WHP AND a 1/4 missing impeller on the hot side (turns out we swallowed a piece of our manifold in the recent past...or something).

Not to mention the points lost for the class and years series.

I've put this in the race section because the focus is purely race, not road.....and im more interested in actual experience and race mindset than guesswork and road knowledge....please correct me if i'm wrong and i'll repost in the drive train section.

Initial sign of trouble was shifting from 5th to 6th...not going in to 6th, a few fumbles later it did. Later in the lap wouldn't go 3 / 4th cleanly than 2nd lap 3/4 and 5/6th started becoming worse eventually same lap lost 3/4th completely....

Anyway, I have a few questions 3 days of pouring over threads hasn't resolved.....I have a spare 6 speed but don't know whether to just fit and continue treating the first failure as an anomaly or go back to 1600cc 200 ft lbs and 260 whp (and valuable 6 speed) while we work out a suitable solution (BMW ZF, Mazda FD or whatever).

- At those power levels, and in a very vague way....shouldn't I be under the often "quoted" 6 speed threshold of 300 ft /bs, 350 whp?
-I raise this as the gearbox I was using was 3 seasons old and was rumbling in 5th when cruising on the motorway. Perhaps it was just tired.....?

- BMW ZF would be ideal but it is VERY expensive with $ conversion, Freight AND import duty. Also, looks like it requires a 3.3 or maybe a 3.6 Final Drive....at initial glance (matching top speeds the 3.3 seems the best candidate) are 3.3's available?...I see Miata Roadster tried to do a group buy but didn't take off.....

- A common "trick" down here (Aus and NZ) for Toyota, Mazda Gearboxes (and I think posibly Nissan too) is to improve the strength of the 4th gear cir-clip. Is this actually a potential improvement for these 6 speeds or a waste of time/money?


Any other thoughts or suggestions to consider?

https://cimg2.ibsrv.net/gimg/www.mia...1c1f32e4be.jpg

I've been down a similar path, having blown up two Quaife gearset-equipped 5-speeds on the track. I now longer track that car and have an FMII-equipped MSM for track duties. Before I took the plunge with a second car, I was holding out for a T5 swap, as heavy-duty gear ratios are available from the aftermarket that result in very similar gearing to the Quaife option (which is excellent for high-torque cars). Since then, the KMiata option has become available. I saw the prototype parts at Miatas at MRLS and they look really nice, if a little pricey:


https://cimg0.ibsrv.net/gimg/www.mia...07532c8ba6.jpg

https://cimg1.ibsrv.net/gimg/www.mia...72f781cec2.jpg

https://cimg3.ibsrv.net/gimg/www.mia...2c9466b01d.jpg

https://cimg6.ibsrv.net/gimg/www.mia...eb852bfacd.jpg

https://cimg4.ibsrv.net/gimg/www.mia...af0baaab8c.jpg


That being said, it is a fairly involved kit, with lots of little bits 'n pieces, and it does look to be very well-engineered. In the grand scheme of things, it's not a particularly excessive price for a bulletproof solution.

As for the 3.3 R&P, the initial group buy was for old inventory that turned out to have many failings. Purportedly the manufacturer, which has a good reputation in the aftermarket, is doing a new run that should put things right.

After 3 seasons it did not owe you anything. Pop a new 6 speed in and call it a day.

Pretty much. It's just worn out. No transmission is going to last 3 full seasons if you are actually using it hard - even at stock power I would go through a 5-speed every 12-18mos. You can do the circlip thing, it supposedly helps, but keep in mind that you didn't break your box from power output. You just wore out the shift forks.

When you actually break one due to torque, you'll know pretty quickly. It's not subtle. :)

Why would anyone with big power want to run this transmission? you'd have to run some crazy rear end ratio for ideal gearing. See below:
https://cimg5.ibsrv.net/gimg/www.mia...3beb04a622.png


With a 3.0 final drive(Dont even know where you'd find a ratio that low) it still will only go 1 mph faster in first gear that the Miata 5 speed and with big power(350+) I personally would want to be going 45-50 in first not even looking at the other gears but they should be spread further than a 120hp car. I just dont see the point here. Am I missing sometihng?

Stock 5 speed gearing:
https://cimg3.ibsrv.net/gimg/www.mia...d8e0932a96.png

Yes you are. On a race track 1st and 2nd don't matter. Read the original post.

1st and 2nd are for the pits. And for the love of all that is good in this world, don't quote photos.

Also I believe you can get a 2.73 or lower ratio with the ford 8.8

To the OP - just emailed you a shipping quote per your email.

Sure, we'd love to have a longer first and second gear, but as stated earlier, those gears are for getting out of the pits. 3-4-5 on the ZF trans is near identical to the Miata 6 speed. If you want longer ratios for a street car, that's where the Getrag 260 box comes in (longer top gear than any Miata trans), or the soon-to-be released E46 6 speed parts.

So far everyone that's ordered our kit has opted for a driveshaft for the Getrag rear end, which opens up your available ratios to 3.23, 3.42, 3.73, and 3.91 and gives you a lot more strength. I'm running a ZF 5 speed and 3.91 in my car and it works quite well. Our soon-to-be turbo K20 car has a 3.42.

Yes, a lot of little components are needed to make this all bolt directly into a Miata, and we didn't skimp on quality. Since we did product photos yesterday, here's a picture of a picture being taken just to give you an idea of the quantity and quality of parts that are included:

https://cimg2.ibsrv.net/gimg/www.mia...8e0837e276.png

Thanks David.

I think per Savingtons and K24's advice we will swap in our spare 6 speed and work towards this solution in the new year. Which gets the next 4 race meetings out the way (and xmas).

I don't like having the thought it could go at anytime (not to mention want to push things up to around 350+ whp) so will be doing something for a long term solution and at this point, yours is by far the best option. With the best support :)

I appreciate all your time and effort in the emails and the people who posted here, thank you.

the countdown to ban beings...

Say what?

Not you.

They do when you want a transmission that can do it all(Street, road course, strip, half mile)

My bad but I have more plans than just road racing.

with that low of a ratio I'm not sure how long a 8.8 would last with big power, launches and slicks. Pretty sure that rear end is for the salt flats. Not ideal

For a K-swap this would be ok as you can rev to 9-10k RPMs but a BP cant. I don't doubt the quality it's just the shortest geared 5 speed I think I've ever seen.

OP of this thread is a road racer. Thus the discussion regarding ratios appropriate for a road race car. If you want to talk about your car and your setup, do it in your thread.

^That. There are general gearbox threads. And you have a build thread. No need to clutter someone's question thread with useless information.

This is the race prep section.

Fair enough, I can see the draw for strictly road race. Thanks and sorry for the clutter.

OP - I think that's a good move. If/when you have issues with that 6 speed just let me know and we can put something together for you.

Hairdresser - the ZF 5 speed with a stock Miata rear end isn't really meant for a street car. The Getrag 260 is geared much longer so if you're not wanting to swap the diff, that's the winner (or an E46 6 speed). If you are swapping diffs, just pick the ratio that's most desirable for your application (probably 3.23 or 3.42).

I run the 6 speed with a stock 5 speed rear end ratio.. what is it 4.1? I Know everyone goes with a taller rear but for a track car that just shifts load to the shorter gear which adds stress right? the shorter rear is not ideal but seems to work pretty well for my modest power car . does it suck on the street going to the track? heck yes but at 70-75 it is not so bad. I drive right about the speed limit on the street which is perfect in car that might attract some unwanted attention. the car theoretically runs out of gear at around 125-130 mph @ 7500. totally fine because I'm not seeing those speeds anyway. the down side was a problematic 4 to 5 shift however that issue nearly disappeared once I went to the Ford trans fluid. the 4-5 and 5-6 gets a little muddy late session so I believe heat is the issue and better heat shields on the exhaust will help going forward. not sure this really helps anyone except those with lower power but if you've blown the 6 and are on a budget perhaps reconsider the short rear. for track days. If mine pops, I'll replace and revisit in 3 years.

Okay, gearbox apart and it appears that it did fail from power in the standard manner, broke cir-clip on 4th gear ....see pic. Apart from some collateral damage all the gears look to have been in pretty good shape prior. Gearbox unusable now though.

A company here (as mentioned in 1st post) does the cir-clip mod. They say the cir-clip mod, heavy duty bearings, deglaze of gears and blueprint the synchro's will cost $1400.00. they reckon that will go a long way to fixing the issue.

So we are going to try this route first as it is by far the cheapest option at this stage.

They also strongly recommend REM treatment of the gears....anyone have any thoughts about that process and the suitability of it for our cause? another $500.00.



https://cimg6.ibsrv.net/gimg/www.mia...c69ffede8d.jpg