6 speed transmission #4 go boom.
 

This time new failure mode. Stripped second gear instead of 4th this time. Newish 275 A6 hoosiers nice 80 degree day on a super grippy lot. Car was ridiculously fast until that happened near the finish of my first autocross run.

Sure wish somebody would make a proper solution with good gearing for this weak link.

whatever happened to your s15 box project?

I still got it I just havent put in the effort yet to work out the details and Im trying to keep the car running week to week as Im racing it.

Have you torn it down yet? I'd bet 4th gear only survived because you weren't using it this weekend. If 2nd had held together, 4th would have blown for sure on the first day of the NASA TT this weekend.

How much torque do you run with the auto-x boost setting that you nuked 2nd gear?

I do run less power for NASA than I do autocross. I turn the boost down.

This transmission might have been a little suspect as I built it myself out of two damaged transmissions. The first transmission I broke actually had a thrust retainer failure and the gears were fine on one of the shafts where as a 4th gear strip out takes out the other shaft.

It's about 310 ft-lbs from 4300 rpm to 6500 rpm. graph is where I have my boost cut set so its a bit under that.

https://www.miataturbo.net/attachmen...0139_small-jpg

Just finishing up my build and found this post and the other 6 speed post. These two post have me worried and after some research I found this. Seams like a good high HP and T fix. I emailed them and I
Was informed this will fit in the Mazda box. They will even make custom hear ratios. It's a lot cheaper then the Nismo box as well.

http://www.par-engineering.com/Products/Catalog/ProdID/410/CatID/120/FS6R92A_1st5th_Synchromesh_Engagement_gearset.aspx

I believe Emmilio tried to get something out of PAR a while ago. don't knowo if that is who he has been talking to more recently. that is the 5 speed not the 6.

Bob I have some ideas on transmission stuff. You might entertain the ideas. Shoot me a message.

It is for the 6 speed AZ6 they don't include the #6 gear. For an extra charge they will. These are the hp levels they quoted me for each. Should hold up. At the bottom of the page they post the standard gear rations. I will have to call Emilio to see if this is the set he was looking at.

" Hi,
Approximate ratings for each,
Dog sets 1000hp, 800Nm
Synchro 800hp, 650Nm.
Are you using the gear set for street driving or purely track use?
Since the transmission is an Aisin the same as used in nissan and mazda certain models besides the input and output shafts the prices can be found on ur site,
http://www.par-engineering.com/Products/Catalog/CatID/120/S15_Silvia200SX.aspx "

bbundy is Bob.. ;)

I don't know much about it since I haven't had to look into this at my power level but I've heard more than one time about the RX-7 trans mounting up with an adapter plate and handling much more power. Not a good solution? Bad gearing?

-Ryan

Bad gearing and heavy was what I heard. And requires custom parts at input and output ends. A custom gearset in a factory box would be perfect in many ways.

The 6 speed aint exactly light, its like 12 pounds heavier than the 5 speed. Almost 90 pounds.

PAR does make 6 speed gearsets in either synchro or dog setups. It is 6-7K for the gearsets. So not exactly cheap. If emilio wasn't working on a cheaper set of gears I would have gone this way, but I have a couple of extra 6 speeds so I am not in a big hurry.

for that kind of money just a bit more gets you a sequential box.

6-Speed Heavy Duty In-Line RWD Sequential Gearbox with Helical Gears

Only 375hp though, and needs a bell housing.

Quaife makes a BP bellhousing, IIRC. The QBE69G box is rated for more torque as well. Bring your checkbook to the tune of $10-12k for a QBE69G + bellhousing + diff mount + driveshaft + trans controller.

Yeah it was like 12K or even more if you wanted other bells and whistles when I priced it out for the QBE60G. When I talked to Quaife in the UK they seemed to think that the QBE60G would be sufficient. The QBE69 was like 13K alone for just the transmission.
The bellhousing is not made by quaife, when I called Quaife USA they said they didnt make one but Quaife UK gave me the information, I have it written down somewhere.

And a Quaife box is never perfect the first time out. Be prepared for adjustments and improvements after 5-10 hours (a couple times).
Quaife and Elite are low end racing boxes...

PAR gears in the AZ6 is a different ballgame of complexity (but can be assembled less than perfect of course).

And a Quaife box is never perfect the first time out. Be prepared for adjustments and improvements after 5-10 hours (a couple times).
Quaife/Elite are low end racing boxes...

PAR gears in the AZ6 is a different ballgame of complexity (but can be assembled less than perfect of course).

Sorry Bob. I fixed the post.

Is it naiive of me to think it's absurd that a solution can't be found to handle 400 whp?? It's monster power to us miata guys but it's really not that much in the bigger picture. This whole $12k to get a transmission that doesn't implode from <400 ft-lbs seems ridiculous. There has to be a solution.

-Ryan

If you don't care about ratios there are several that just need fabbing (mounts, adapters/bellhouse) to get in there.
A contributing problem is that the stock ratios are really good and if you do something why make it worse.

PAR gears seems to be the cheapest/convenient "solution", currently. But no one here knows how long it will hold (it will fail for someone for some reason at some time of course).

After 3-4 6 speeds I'd have put one of those solutions in and adjusted ratio at the diff to make it work...

Gears don't work like that.

two spead rear end? :party:

Is there a reason why you track guys are against 4 speed, with the quicktime bell housing and something like this

G-Force Transmissions and Long Shifters

i would think that its a far cheaper option then custom gear sets or sequential gear boxes. I find it hard to believe you can't get ratios to work with the amount of custom ratios for 4 speeds and rear ratios for our diffs.

That's the option I was considering before I decided to build a street car. I think a T101a with some sort of powerplant adapter might be a good option, although not for a street car.

I was interested in the Richmond 5 speed road race transmission. They now make a 6 speed as well and with a fair number of ratios.

I could definitely make a box with fewer gears work for either track or autocross but not both from anything I have seen. Autocross is easy you only need two gears one low gear to launch and one that will hit right around to 70Mph with an elevated rev limit.

interesting I think you could build one with good ratios. why have I not seen that before?

http://www.richmondgear.com/pdf/RG21.pdf

That might work nicely with a 3.909.

Richmond ROD 6 speed
Gear ratio Mainshaft countershaft
Drive - 22 37
1st 3.043 38 21
2nd 1.993 32 27
3rd 1.570 28 30
4th 1.237 25 34
5th 1.000 - -
6th 0.857 26 51

looks like it might be about 50-60 lbs heavier than an AZ6 by the time you get the bellhousing and taileshaft mounting setup.

Sorry to hear about your trans problems. Subed for more info.
Is the RX-7 turbo 2 trans too much fab work to mess with? Bad gearing choices?
Any potential advantages to cryo treating if your building another 6 speed?
What are you currently using for rear end and half shafts?

-Jeff

Qnce again. RX7 turbo 2 has awful freekin gearing for track use. way too big of rpm jumps in the 70-150 MPH range. I believe id loose a second or more on several tracks not being able to match shift points with track layout.

https://www.miataturbo.net/attachmen...-rx7tii410-png

What about 2.42, 1.53, 1.23, 1, .75?

If picked right a 6 speed will have 2 useful gears for autocross and 4 useful gears for the track. A 5 or a 4 speed can be optimized for one or the other but not both. The stock gearing in the 6 speed is Ok but I think it would be improved if it were closer ratios still. Second gear needs to be slightly taller for autocross and I think slightly less rpm drop between shifts 3-4, 4-5, and 5-6 would be faster on the track. On the track you really sort of want it to where being in any of two different gears at critical points will keep you on the power curve so you can adjust shift points to match for both the track layout and speed while staying at RPM’s that have the most throttle response and power.

Pretty crummy jump between 4th and 5th. still looks bad to me with a 4.10 or 3.909. Best 5 speed gearing speed seems to be the Quafe wide but even that I think can be optimized for the track or for autocross but not both with the same rear end ratio. I just get enough speed out of second with the 6 speed 3.636 combo for autocross by turning up the rev limit to 8600 rpm Im not quite sure how much taller I can go before loosing power and throttle response for slower corners cost significantly. My guess is not much like 5mph more max. I have been over geared with the 5 speed for autocross before and it was an eye opening experiance with lower gears and a higher rev limit. Top speed is not important enough to sacrafice power and throttle response on the rest of the course but shifting to 3rd sucks.


https://www.miataturbo.net/attachmen...-mystery-5-png

Perfect, except 5th is a little deep as Bob said.

Read this thread, especially from post ~125 onwards, for a lengthy discussion of what gear ratios are ideal and why they are ideal.

https://www.miataturbo.net/suspensio...es-dust-75506/

the 'mystery transmission' is a G-Force T5 gearset
G-Force Transmissions GFT5242-93S G-Force T5 Transmission Gears And Mainshaft Upgrade Kits - Free Shipping on All Orders @ JEGS

you can also get a 0.82 fifth gear which should work better than 0.75
G-Force Transmissions GFT82 G-Force T5 Transmission Gears And Mainshaft Upgrade Kits - Free Shipping on All Orders @ JEGS

g-force also makes a ballertown T5 Ford case
G-Force Transmissions GFT5072 G-Force T5 Transmission Case Upgrade - Free Shipping on All Orders @ JEGS

https://www.miataturbo.net/attachmen...ine=1402940146

That box can also be had with 2.94, 1.94, 1.34, 1.00, .82 which I really like, lets me keep the 4.10.

for comparison.

https://www.miataturbo.net/attachmen...quafe-wide-png

Also for discussion Last night I peced together a gearset in that Richmond 6 speed. It can be made very close to what can be found in the NISMO AZ6 or it can also be made very close to the stock Miata 6 speed with a taller 1st and 2nd. first time I seen anything like that that you can get the gearing right in. cost about $3700 from summit for the box. I think you can buy the bellhousing to fit it to a BP from summit as well.

I keep forgetting that we're always talking about BPs specifically. I look at the TII gearing and say "that's not too shabby."

if you are using primarily for autocross in SSM I think you would want the 5.125 rear end with those gear ratios. selecting a second gear that is usable on the track for slow turns on the track means its way too tall for autocross unless your car has awsome power and throttle response starting at 3000 rpm or the speed range on your autocross course is between about 50 and 95 mph.

I think those ratios would work quite nicely for a high power track car.

1.94 2nd gear with the 4.10 and 275s is like a 71mph top speed with 8500rpms. I might consider the 3.9 with it.

Oh my bad I still had the 1.53 second in my spreadsheet. you would have a decent autocross box and just 3 gears for track use though.

Which takes us back to needing a 6 speed to have a good auto-x box and a good RR box. Like the Richmond Gear 6 speed with the 1.125 x 26 spline input shaft

2.77, 1.88, (1.67, 1.52, 1.46, or 1.36), 1.19, 1.0, 0.84

This is like a $3900 tranny, dry weight of 108lbs. So its a weight gainer compared to our 6 speed but you'll never have to think about it again. A a bonus, the fitment we want is the C4 vette which also has a pickup for a torque arm that was should be able to make a ppf adapter for.

yea if I was going to do an autocross only box I would go 2 or 3 speed I think.

Subscribed to this one too.

Those are the standard T5z ratios on 1-4, and a ~$200 5th gear option. Changing 5th does not require disassembling the main transmission body, just removal of the tailshaft piece. T5z is a very affordable transmission and strong enough for anyone on this site.

I'm running it with my 3.90. I'm not a track guy but it's nice on the street. The standard .63 5th is a HUGE drop in rpm. I'm at ~2700rpm at 75mph, which is nice but the .8x 5th is on my to-do list.

Tim, is the T5z supposed to be stronger than the T5WC? The T5WC would break around the same torque as the 6 speed.

T-5z is the world class trans. Technically a 330ft-lb capacity in a heavy mustang doing dragstrip yank the wheels launches with dragradials.

I know of racers running significantly more than 330ftlbs thru them on the strip.

But yeah maybe, apples/oranges application. Maybe the extra heat from road racing will cause damage in similar time to the 6 speed. That would suck.

I guess. I thought fox bodies could still lunch the world class tranny in stockish form on early 90's era street tires though, they just did it less often than the older fox bodies that came with the non-wc t5.

I keep thinking about BP to T5 adapter.
Here are my thoughts:
- Most common Ford T5 has 17mm tip of input shaft. Miata pilot bearing is 35mm OD. Fastenal has a bearing just that size
- T5 pilot bearing (at least on Ford transmissions) goes into the block while Miata pilot bearing goes into the flywheel. This gives enough offset for an adapter plate that would sit between stock T5 bellhousing and BP block.

Ideally, the adapter plate would sit between miata bellhousing and T5 because it has a simple, easy, 4 bolt flange. But miata transmissions don't have separate housings, the whole front part is one piece.

BUT!
There are also automatic miatas, right?

http://gaiazov.com/photo/mt.net/miat...ellhousing.JPG
90 93 Mazda Miata Automatic Transmission | eBay

This is a 90-93 automatic transmission and it appears to have a very nice, separate bellhousing. Now, its an auto so there is no provision for a clutch fork. But thats a much, much simpler problem than not having a bellhousing, imo.

Further research shows that only NA automatic transmissions have that bellhousing, the NB transmissions are different.

Maybe lakewood can be re-drilled for the T5 to mount to it.

Lakewood bellhousing is 20lbs and $700, fuck that shit.

also
MX-5 Miata Forum - View Single Post - A question regarding interest

https://fbcdn-sphotos-e-a.akamaihd.n...53187424_o.jpg
https://fbcdn-sphotos-h-a.akamaihd.n...62057424_o.jpg

I am also looking into this and have one of the T5 rebuilders commenting yesterday
"I was able to confirm that the Quicktime RM4097 bell housing will bolt
to the 88-92 Camaro T-5 case and would expect to have the Camaro size
input shaft! "
Yes it is $600-700 for the bellhousing and it will be steel, but it is readily available and claims that it does not require further fabrication.
G-force has apparently stopped producing dog ring gear sets for T-5, too many issues with people wearing them out and asking for warranty rebuilds.
Looking for other vendors providing straight cut dog ring gearsets for T-5...

Are you looking for straight cut gears or dog ring? I don't know if g-force ever had a straight cut gear set... they only show helical dog ring and helical synchronized. No straight cut gears...

You can get a faceplated TKO600 from Liberty's Gears. It should also bolt up to the Lakewood housing. They could faceplate any other transmission, e.g. T5 or whatever. New Page 1

As far as I understand, faceplated and dog ring is more or less the same thing.


edit: google shows that g-force did have straight cut gears circa 2008 (?)