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Old 05-07-2012, 09:29 AM   #1
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Default blew a tranny this weekend

the second session in the morning of a three day event. awesome.

so what is the typical fail point. I was in third gear, heard a high pitched sound and then no gear. im going to send the oil in to black stone to see if heat caused a break down.

any advise? not sure I want to go 6 speed,
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Old 05-07-2012, 11:17 AM   #2
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You probably want to go 6-speed.
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Old 05-07-2012, 11:57 AM   #3
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If you want to stop breaking transmissions as often, you want to go with a 6 speed.
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Old 05-07-2012, 01:03 PM   #4
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well how often are people who track hard breaking their trans? I got the car, did 2 pretty easy sessions and 2 pretty hard sessions and it is toast.

I guess their is know way to really say.


do we we know the root cause of the failure? was someone taken it apart and looked at what is failing it? if it is just too much power fine, but seems like it could be heat related, the shifter under the ---- boot was very wet with fluid, perhaps it was overheated or perhaps the previous owner over filled it?
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Old 05-07-2012, 01:07 PM   #5
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There is supposed to be fluid there in the 5-speed, people break 5-speeds ALL THE TIME, and the failure mode is just too much torque. You're not that new here, how do you not know these things?
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Old 05-07-2012, 01:08 PM   #6
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From what I've read, people who track turbo Miatas with 5 speeds see that transmission as a consumable.

The bottom of the shifter is supposed to be wet with fluid on a 5 speed.
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Old 05-07-2012, 01:18 PM   #7
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Originally Posted by MartinezA92 View Post
From what I've read, people who track turbo Miatas with 5 speeds see that transmission as a consumable.

The bottom of the shifter is supposed to be wet with fluid on a 5 speed.
It really is if you track a miata then the 5 speed is a consumable. Having a turbo does not change that.
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Old 05-07-2012, 01:23 PM   #8
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A couple of buddies and I tend to agree that the 5spd due to the PPF will twist and and stretch the case resulting in blown gears. Looking at the ribbing on the 6spd.
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Old 05-07-2012, 01:23 PM   #9
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I watched another member here (cordus) blow 3rd (iirc) out of his 5 speed on the front straight of MRLS about a month ago. He's running a similar setup (FMII, 2560, 3" exhaust) so yes... at your level on the track, its not unheard of.

FWIW, I believe he's going 6 speed.
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Old 05-07-2012, 01:28 PM   #10
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Quote:
Originally Posted by psreynol View Post
I guess their is know way to really say.
I'm about to throw up.

You most likely did what the rest of us did, which is sheering teeth off the gears. Same thing happens in 1.6 rear ends, at least mine did. I'm sure if an oil cooler made a 5spd reliable we'd all run $300 cooler systems over $700 transmissions, but that's not the case. And as much as I'd love to be proven wrong, cooler oil doesn't keep teeth from snapping off.
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Old 05-07-2012, 03:13 PM   #11
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There is supposed to be fluid there in the 5-speed, people break 5-speeds ALL THE TIME, and the failure mode is just too much torque. You're not that new here, how do you not know these things?
fair enough, but Ive only been here a few months and Ive spent a ton of time reading about every trouble spot on a track turbo miata and personally I think Ive done a good job getting this car track ready. do you track? I do about 15 or days a year minimum usually more, a lot more. Ive worked on my car almost every night for several months so cut me some slack. I know the 5 speed trans failure is common but Ive not ran into posts about specifically what is failing so just want to find the most cost affective way to make the trans reliable.

Im going to open the box and see what happened. just wanted some basic info and no one said anything about the different versions of the trans and perhaps changing out 3 for a stronger gear.


someone said I needed real brake pads. I had zero brake problems with willwood E fronts and HPS rears. it is shocking to me as well but Autobahn is not that hard on brakes so I'll see what is needed when I do blackhawk in a couple weeks. fyi the alcon temp strips on the caliper did not even darken one block

Last edited by psreynol; 05-07-2012 at 03:29 PM.
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Old 05-07-2012, 03:17 PM   #12
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Quote:
Originally Posted by psreynol View Post
fair enough, but Ive only been here a few months and Ive spent a ton of time reading about almost every aspect of the car so cut me some slack. I know the 5 speed trans failure is common but Ive not ran into posts about specifically what is failing so just want to find the most cost affective way to make the trans reliable.
The most cost affective way to make the trans reliable is to spend the $600-$1000 for a 6 speed.
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Old 05-07-2012, 03:43 PM   #13
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Originally Posted by curly View Post
I'm about to throw up.

You most likely did what the rest of us did, which is sheering teeth off the gears. Same thing happens in 1.6 rear ends, at least mine did. I'm sure if an oil cooler made a 5spd reliable we'd all run $300 cooler systems over $700 transmissions, but that's not the case. And as much as I'd love to be proven wrong, cooler oil doesn't keep teeth from snapping off.

well with my limited experience on gear failure fluid temps can have a major affect. In FSAE we had lots off diff problems due to oil, we had lots of diff failures in a diff that was designed for a very heavy car. when the teeth mesh well all is fine but with added heat in time the gears wear and they dont mesh right then they fail so anything that can be done to slow that wear will extend their life significantly. once the wear starts it is all over.

I'm sure much of this has been tried but I asked about trans temps and I did not see a good answer. please dont throw up, just trying to learn from people who really ring out their cars at the track. if the 6 speed is the answer then fine I will do it but I just want to know the details before spend the money on a box with 6 gears when I only need the 5.
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Old 05-07-2012, 04:53 PM   #14
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I almost blew out my colon this morning.
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Old 05-07-2012, 04:57 PM   #15
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I think they have other forums for that.
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Old 05-07-2012, 05:16 PM   #16
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Quote:
Originally Posted by psreynol View Post
if the 6 speed is the answer then fine I will do it but I just want to know the details before spend the money on a box with 6 gears when I only need the 5.
You broke the 5. You need the 6. This is much, much easier than you are trying to make it. The failure mode is broken gear teeth, usually in 2nd under power or 3rd after a hard shift. The 5-speeds break at 200whp with abuse, or at 250whp without abuse. Fluid temps probably make it worse, but there are autocross cars that break 5-speeds too. There's a guy in Washington (bbundy) who broke SEVEN of them before finally giving up and switching to a 6-speed.

The 6-speed is bombproof at 300whp, and it starts to become a consumable (once every 12-18months) at 350+whp. At your power level (FMII) it will last pretty much forever.
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Old 05-07-2012, 06:20 PM   #17
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You broke the 5. You need the 6. This is much, much easier than you are trying to make it. The failure mode is broken gear teeth, usually in 2nd under power or 3rd after a hard shift. The 5-speeds break at 200whp with abuse, or at 250whp without abuse. Fluid temps probably make it worse, but there are autocross cars that break 5-speeds too. There's a guy in Washington (bbundy) who broke SEVEN of them before finally giving up and switching to a 6-speed.

The 6-speed is bombproof at 300whp, and it starts to become a consumable (once every 12-18months) at 350+whp. At your power level (FMII) it will last pretty much forever.
ok got it, it was not a hard shift but a nice easy rev match down to 3 and, back on the gas on a kinda double apex and when I squeezed the throttle on track out I got a weird wine and a pop clink clink, almost like a linkage came apart. took it apart and no linkage in this trans, shifter goes right into the trans.

I have way too much work to do on this car to ---- around. I still want to think temp and good fluid management could be the answer but it sounds like other have been down this road despite not not seeing any temp numbers. whatever if it will last Ill do it, think I found a 50k unit for 700 not to far from home. guess I should get it and not look back.

I have several events coming up, every weekend in june and I need to get this thing reliable this year. a friend and his f-in cup car need to be put down now he he ....> (thinks a turbo miata can not be reliable on the track.,,,,, going to prove the sob wrong )

on to suspension, cant buy coils, thinking spec miata even though I know its not great at least it work for the season and I can sell it easily

Last edited by psreynol; 05-07-2012 at 06:41 PM.
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Old 05-07-2012, 07:23 PM   #18
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I just talked to dave at red line and he was very helpful in general terms about the mt-90 trans fluid recommended for our trans.

a recommended fluid temp is about 190-195f - at that temp the viscosity is 19.5
for comparison 300f it is 6.5 at 330f it is 5.3. - the temp people have seen on the trans housing via temp sticker

so we know a temp over 300f is well into the range a cooler is needed. a viscosity drop in a engine like this would be scary. this is is why many run a fluid that has a high viscosity when hot. Ive been running motul 300x 15-50 for this reason, my motor gets hot! keeping the temps down to around 200f would make sure the fluid is doing its job and not turning into water.

this is not to say a trans failure is not going to happen but it does suggest that heat is the real enemy of the trans, and not necessarily the power. I think our trans would do much better with a cooler but buy how much I dont know.

fabricating a oil cooler for the trans is not hard, nor is it easy and the cost might be a wash when compared to doing the 6 speed. I;m on a time crunch so I may just do the 6 speed but I do think this deserves more exploration. If Ive missed the boat speak up but without track testing I dont care. I want to see a new 5 speed run at about 200F and see how long it lasts.
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Old 05-07-2012, 08:05 PM   #19
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Originally Posted by jacob300zx View Post
A couple of buddies and I tend to agree that the 5spd due to the PPF will twist and and stretch the case resulting in blown gears. Looking at the ribbing on the 6spd.
This is an interesting theory and makes some sense. If the case flexes the right way, it would move the shafts apart which reduces the contact area of the teeth (making them easier to shear off). High horsepower Honda's use a handcuff to reduce shaft separation but it converts the gearbox to a 4 speed (not recommending that as a solution, just showing a similar problem exists in other applications).

I understand the 6 speed is the easy way to go but I also like the idea of fixing a problem. Please post some pictures of your trans when you pull it apart.
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Old 05-07-2012, 08:06 PM   #20
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I work at a shop that builds high performance, upgraded trannies (DSM, Evo, 3S, Supra, the occasional RX-7). The number one killer of gearsets is torque, and the only way around it is higher strength parts. Tolerances, preloads, specific detailing, etc can be adjusted to make sure a trans shifts as well as possible which can help a bit. There are a few ways to upgrade a DSM trans, for instance, with higher strength gears/shafts so that they are good to about 600whp, but that's it. Beyond that, nothing else has been shown to help. There is a limitation to any material that is subject to high stress for extended periods of time, and the 5 speed Miata gearbox apparently was just not designed to take much abuse.

That being said, I'd guess in a roadrace situation higher trans temps can and will play a part in the deterioration of the oil, which will lead to greater wear on contact surfaces, and the extended time heatsoaked could probably lead the gears to fatigue and fail sooner. The only time we've modified a manual trans for an external cooler was on the Chumpcar we ran a couple years ago, and that was due to the fact that it was going to be run in an enduro, not just 30 minute sessions. It was not a simple procedure, requiring the addition of a mechanical pump inside the trans, case modification and welding, etc...pretty much no room to do that with a Miata trans as far as I can tell.
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