Another 6 speed bites the dust. - Page 14 - Miata Turbo Forum -Boost cars, acquire cats.

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Old 11-15-2013, 03:54 PM   #261
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5x6=30
That's not what I said
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Old 11-15-2013, 04:08 PM   #262
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you were also wrong
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Old 11-15-2013, 04:11 PM   #263
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Another 6 speed bites the dust.-bth_why-so-serious.jpg  
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Old 11-15-2013, 08:09 PM   #264
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That's not what I said
precisely
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Old 11-15-2013, 08:09 PM   #265
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actually you both are wrong, the correct answer is 31 forward unique gear combinations (because reverse and reverse will also yield a forward gear combination); 11 reverse combinations; and 1 neutral combination
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Old 11-15-2013, 08:11 PM   #266
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actually you both are wrong, the correct answer is 31 forward unique gear combinations (because reverse and reverse will also yield a forward gear combination); 11 reverse combinations; and 1 neutral combination
well dam, im speechless
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Old 11-15-2013, 09:28 PM   #267
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I dont know fro sure but I have broken seven of the 5-speeds and three of the 6-speeds.

In the five speeds ive broken second gear, third gear, and the primary gears. also had rapid failures like after two weekends.

the six speed I have broken 4th gear twice and screwed up a bearing on the secondary shaft once which might have been caused by a thrust washer for 4th gear breaking off the teeth on the reverse gear teeth on the secondary shaft.

I have never had any issues with Sycro's. don't even see any wear on them.
is there any visual physical difference [size, heft, cut angles, ???] between the 5-speed gears compared to the 6-speed gears?

is there any composition difference between the two sets?

what part of the gear breaks?
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Old 11-15-2013, 09:43 PM   #268
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is there any visual physical difference [size, heft, cut angles, ???] between the 5-speed gears compared to the 6-speed gears?

is there any composition difference between the two sets?

what part of the gear breaks?
The teeth strip off the gears. usually happens suddenly while accelerating when engine reaches around peak torque. it has nothing to do with making hard shifts. has allot to do with engine torque capability and stickyness of tires.

small differences can make a huge difference in life. the gears look similar between the two to me in size but things like case flex and shaft flex could have a major impact as well. The five speed has several failure modes all at around the same torque level. The six speed seems to have one weakest point in the 4th gear. this leads me to belive the RX8 gearset is stronger because that is the only gear ratio they changed.

Some say sprung hub clutch makes a difference I have broken with both sprung and unsprug. On the 1.6 l size clutch like I am using the sprung ceters are not durable I have found they spend a lot of time with the springs bottomed out and otherwize behave more like a slide hammer than a vibration or impact isolator.
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Old 11-15-2013, 11:55 PM   #269
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Dont the rx8 internals have carbon fiber synchros? If so, then eff measuring stuff, just slap that beauty in!







Though it would be nice to verify once and for all whether or not the s2000 synchros are applicable.

Last edited by glade; 11-15-2013 at 11:56 PM. Reason: brainfart
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Old 11-16-2013, 05:50 AM   #270
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Originally Posted by bbundy View Post
The teeth strip off the gears. usually happens suddenly while accelerating when engine reaches around peak torque. it has nothing to do with making hard shifts. has allot to do with engine torque capability and stickyness of tires.
It goes something like this:

https://www.youtube.com/watch?v=NINRy4u7x_g#t=0m13s

--Ian
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Old 11-16-2013, 06:07 PM   #271
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Originally Posted by glade View Post
Dont the rx8 internals have carbon fiber synchros? If so, then eff measuring stuff, just slap that beauty in!







Though it would be nice to verify once and for all whether or not the s2000 synchros are applicable.

if i could get a set of s2k synchros i could measure them while mines apart
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Old 11-16-2013, 11:43 PM   #272
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Quote:
Originally Posted by bbundy View Post
The teeth strip off the gears. usually happens suddenly while accelerating when engine reaches around peak torque. it has nothing to do with making hard shifts. has allot to do with engine torque capability and stickyness of tires.

small differences can make a huge difference in life. the gears look similar between the two to me in size but things like case flex and shaft flex could have a major impact as well. The five speed has several failure modes all at around the same torque level. The six speed seems to have one weakest point in the 4th gear. this leads me to belive the RX8 gearset is stronger because that is the only gear ratio they changed.

Some say sprung hub clutch makes a difference I have broken with both sprung and unsprug. On the 1.6 l size clutch like I am using the sprung ceters are not durable I have found they spend a lot of time with the springs bottomed out and otherwize behave more like a slide hammer than a vibration or impact isolator.
Thank you
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Old 11-17-2013, 10:51 PM   #273
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Quote:
Originally Posted by mx594m View Post
actually you both are wrong, the correct answer is 31 forward unique gear combinations (because reverse and reverse will also yield a forward gear combination); 11 reverse combinations; and 1 neutral combination
Actually, there's 3 neutral combinations.
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Old 11-18-2013, 03:30 AM   #274
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Actually, there's 3 neutral combinations.
I make it 14 non-driving combinations (6+R, 5+R combined with neutral on the other box and the dual neutral). But a normal neutral would be neutral on the first box, to not spin that much stuff.

Does anyone have view on the cost of making a one-off pair of gears (4th in this case)? Sure, whole sets cost a bunch but if "only" one pair would be needed (until the next failure point if found of course) could you imagine getting it below $1k (making 5 pairs maybe)?
Having a box that have straight gears on only one pair will sound strange of course

I assume the RX8 4th gear pair don't fit (dia, width, splines,...), since it would be done by now (and it's probably mentioned in this thread already).
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Old 11-18-2013, 08:22 AM   #275
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Before we go on making a bunch of gears. Lets get a bunch of strain gauges on the outside of the case to make sure the case isnt just flexing apart and thats whats killing the gears. If it is the case flexing, making a clamp or brace to prevent it will be a heck of a lot easier.
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Old 11-18-2013, 11:22 AM   #276
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Originally Posted by Leafy View Post
Before we go on making a bunch of gears. Lets get a bunch of strain gauges on the outside of the case to make sure the case isnt just flexing apart and thats whats killing the gears. If it is the case flexing, making a clamp or brace to prevent it will be a heck of a lot easier.
This, I have several times myself wondered if it wasn't a case flex issue. (BTW, RX-8s don't have carbon fiber syncros, or they would be in my car).

I had never given the 4th gear issue any though, but I am putting together a 6 speed with some rx8 parts where I could use the 4th gear from the RX-8. I don't track my car though, so we shall see.
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Old 11-18-2013, 12:42 PM   #277
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This thread reeks of the gay.
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Old 11-18-2013, 12:42 PM   #278
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3rd and 4th are part of the mainshaft, along with the counter 4th gear it would be alot more then a thousand. The case could come into play, but after looking at Bob's trans and seeing how thin the teeth are on 4th, I think it has more to do with the gear then the case.
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Old 11-18-2013, 03:11 PM   #279
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Originally Posted by chicksdigmiatas View Post
This, I have several times myself wondered if it wasn't a case flex issue. (BTW, RX-8s don't have carbon fiber syncros, or they would be in my car).

I had never given the 4th gear issue any though, but I am putting together a 6 speed with some rx8 parts where I could use the 4th gear from the RX-8. I don't track my car though, so we shall see.
Pretty much got to use the whole gear set from the RX8 to get the assumed stronger gear. 4th is machined right on the main shaft. I think you might be able to swap the input shaft and main gear between the two to allow using a standard off the shelf Miata clutch. Miata clutch has a 15/16X 22T input and RX8 has a 1"X23T

FWIW the 4th gear in the RX8 is odd ratio spacing compared to the Miata. I think it was done entirely for strength. The Miata has a slightly better ratio with even rpm drops between 3rd, 4th, 5th shifts but little tiny fragile teeth on the 4th gears to get that ratio.

ALSO I think the strength issue of 4th gear is dramatically diminished if the car doesn’t see the track. Almost never do you get the opportunity to do a full power run through the rev range in 4th gear for any kind of sane street driving even if you typically drive like a jackass every day to work. Especially combined with super sticky DOT Slick tires whereas on a track you could do it 3 or 4 times per lap.

Last edited by bbundy; 11-18-2013 at 05:10 PM.
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Old 11-18-2013, 03:22 PM   #280
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One more random thought

In a Saker racecar I know of there was problems with a bending Subaru gearbox since the exhaust was routed above it. Better shielding, greater distance and some airflow solved the problem.

Just guessing if the exhaust heat could bend the case to make it more prone to failure, or would that flex be in a non affecting direction (bending left/right not up/down)?
Keeping it cool would not hurt anyway and Bob is not cooking it worse than anyone else (but you cook it a lot worse on track than on the street/DR).
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