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Old 10-14-2013, 01:51 PM   #1
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Default Another 6 speed bites the dust.

Ok after doing a replacement of my 6 speed earlier this year in the paddock at Laguna Seca putting in a Mazdaspeed version. I stripped out 4th gear again. This time on the back straight of Portland International, full throttle at peak torque in forth and bang strip. I wasnít even running the motor at full tilt. I have it tuned to do 20psi but Iím running 14-15 psi making 324 HP and I think it was 280 ft-lbs to fit into NASA TT2. I have recently set overall Miata lap records with it on 3 northwest tracks winning NASA and SCCA time trials and also won a couple national events in Solo as well as the Canadian Solo National championship so it has been driven hard.

Trying to decide what to do next. 6 speeds are expensive when you go through 2 a year!
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Old 10-14-2013, 01:59 PM   #2
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Any gearbox alternative would cost at least four 6speeds (including the quife gears ready to go), but if it would work for at least two years it would be worth it (less lost days etc).

How many general US race boxes have been modded into Miatas (non-PPF of course)?
Anyone used these (with a useful road race box etc etc)?
http://www.jegs.com/i/Quick-Time-Bel...-4097/10002/-1

Sorry, I have missed this one (no answers but a lot of the usual speculations)
4 Spd Jerico w/ '99 Motor

Last edited by NiklasFalk; 10-14-2013 at 02:18 PM.
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Old 10-14-2013, 02:25 PM   #3
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To continue to verify my ability to spit out nonsense:

Would a lower final gear help anything, putting the long high torque loads into fifth (i.e. no gears to strip if I have understood gearboxes at all)?
This would of course make 1st a loading gear and 6th maybe a bit short (thinking 4.44 or so).
Cheaper test than a custom gearbox, if there is any possibility that it could work.
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Old 10-14-2013, 02:59 PM   #4
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It is time to find a better solution. Jerico 4 speed would be great for track duty but you need to be geared in a way that it would not be fun on the street. OTS cheep solutions maybe a T5 or T56?
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Old 10-14-2013, 03:04 PM   #5
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Why not RX-7 5-speed?

An RX7 gearbox seems to be the next logical step, before going full out crazy on a Jerico box or on a Quaife gear-set.

Luckily, the rx7 gearboxes are pretty cheap. Heck, the bellhousing adapter plate is 2-3x the cost of the gearbox itself. You only have to buy the adapter plate once, and you can probably pick up 3 rx7 gearboxes for the price of one six speed...
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Old 10-14-2013, 03:09 PM   #6
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Quote:
Originally Posted by NiklasFalk View Post
Sorry, I have missed this one (no answers but a lot of the usual speculations)
4 Spd Jerico w/ '99 Motor
The answer to using a Jerico is simple.

1. buy that quicktime bellhousing
2. use factory flywheel with a clutch disk that matches a Jerico input shaft
-or-
2. use fancy flywheel/clutch like twindisk jobbies that already have splines that match a jerico

*Jerico has many different length and spline count input shafts. They will work with you on figuring out what you need.

3. Make a trans cross member, pretty simple.
4. Custom driveshaft, pretty simple. Jerico can supply you the front yolk if you want something baller.
5. Custom diff mount/ppf solution, can be simple or not depending on your preference.

possibly 6. Rig up some sort of clutch mechanism depending on how "OE Mazda Miata" that Quicktime bellhousing is in reality.

OH, edit: 7. Shifter. That may require some tinkering.

Most difficult part for most people would be earning the money to do the above.
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Old 10-14-2013, 03:11 PM   #7
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Sorry to hear that 6-speed has tendency to do the same thing as my 4 previous five speeds, break under torque. I am down to 3 working ones so I should be set for couple of hillclimbs

In for gearbox info.
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Old 10-14-2013, 04:12 PM   #8
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Old 10-14-2013, 04:13 PM   #9
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How about using a AVCR boost controller to tone down peak torque a bit? If 4th is the only problem you can detune peak torque only in that gear. Kinda simple solution that will allow you to stick with the 6 speed.

The AVCR allows control of boost by RPM and boost by gear.
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Old 10-14-2013, 04:25 PM   #10
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I'd be interested in finding out WHY you keep stripping 4th. Is the gear not strong enough, case flex, something else entirely? I have no idea how you would go about finding that out without a boatload of money though.
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Old 10-14-2013, 04:30 PM   #11
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150whp crew...
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Old 10-14-2013, 04:37 PM   #12
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Quote:
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I'd be interested in finding out WHY you keep stripping 4th. Is the gear not strong enough, case flex, something else entirely? I have no idea how you would go about finding that out without a boatload of money though.
I am suspecting bearing issues start the problem allowing shafts to spread apart a bit and tip load the teeth. Evedence of repeated failures by me and other High hp Torque users sugest 4th is the weak point in the 6 speed.
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Old 10-14-2013, 05:08 PM   #13
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In five speeds I have broken twice on third gear and once on fifth on track. There has been one time where the gearbox broke on second gear at autocross. Every time the secondary shaft has been used.
Leaves 1 st and fourth, 1st sees torque so short time that it will not break and fourth is straight gear.
Based on tooth angle on quaife set, I suspect also secondary shaft axial loading on stock box has something to do with breaking gearboxes.
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Old 10-14-2013, 05:16 PM   #14
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Bob contact Ron at Barrington Performance

He seems to be on top of custom work for Miata gear boxes. I bet he has a reasonably priced solution to your problem.
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Old 10-14-2013, 05:26 PM   #15
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Earlier there was a thread about the even heavier duty tranny. IIT or ITT or forgot what it was called... if you're going to do an adapter plate might as well do that.
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Old 10-14-2013, 05:27 PM   #16
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Old 10-14-2013, 05:52 PM   #17
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Quote:
Originally Posted by k24madness View Post
Bob contact Ron at Barrington Performance

He seems to be on top of custom work for Miata gear boxes. I bet he has a reasonably priced solution to your problem.
Otherwise good, but is about 10 junkyard 6-speeds and 30 -60 five speeds.
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Old 10-14-2013, 05:57 PM   #18
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Quote:
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Otherwise good, but is about 10 junkyard 6-speeds
Sure but look at the other options that are being thrown out. Keeping the factory case will be lighter and easier. Cost will be around the same as the other ideas being thrown around.
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Old 10-14-2013, 06:37 PM   #19
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Well the main debate is, is replacing transmissions again and again cheaper vs paying the higher cost of a stronger transmission off the bat. Odds are if you've broken 3 transmissions you'll brake another one.
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Old 10-14-2013, 06:56 PM   #20
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Hell, $5500 buys you 10 running beater Miatas to steal transmissions from...

The only reasonable solutions are Shadowconspiracy's T2 adapter plates and the Quicktime bell housing.
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