No wonder none of these companies have gotten back to me after offering to let me prove their durability. Still happy to do some tranny swapping for free, but I ain't buying one of these things until they have survived a few months in my car. Or unless I see someone with a similar car put one through the wringer. I will say that running a stock mass flywheel as Walter suggested seems to extend their life a little.

 

Just wanted to give a little update. Been about a month and a half of abusing this transmission. Car is currently running @ 18psi about 310hp~, 270~ torque (virtual dyno). A lot of WOT pulls, mild launches, accouple of slidy bois.

I'm not the type to baby their project cars either. Driving it hard and countless pulls on this trans.


Transmission feels great, shifting is probably the best I've ever experienced on a Miata trans. Especially the 3rd to 4th. Enjoy banging those gears.


Don't know how long a stock 5spd would of lasted, but so far no issues with mine. It is a street car so the trans isn't really abused super hard.
Will update thread in about 5 months or sooner if trans blows.

Edit: One thing I noticed however, this transmission is kind of a slouch when it comes to shifting at cruising speeds in the city. Feels notchy and kind of clunks.

However when you step on it, it slips right into the next gear so easily. Probably the best feelings driving the car, is the shifting underload.

 

Another update:

After almost two years of constant abuse, I believe the transmission finally gave in...

After my last drifting session the transmission was making a really loud knocking sound. As if the flywheel or clutch plate was loose. After taking the transmission off and inspecting the flywheel and clutch, they looked perfectly fine. Wasn't loose or anything.

However when I drained the oil from the transmission, this piece came out. Which I assume is a tooth of a gear.



I don't believe I completely "blew up" the transmission, as the trans still shifted fine in all gears and I ripped it through all gears when I first noticed the sound to verify if it was coming from the trans or not.

Currently I'm assuming the cause of the loud knocking sound is due to a failed bearing in the trans. Probably the main shaft bearing? In all gears it will make that knocking sound, even neutral, but once you press on the clutch the noise disappears.

Maybe one day I'll take it apart and see what the real damage was, but for now I replaced the trans with a stock 5 speed and probably saving up for a k-miata drivetrain swap.

 

You posted this less than a year ago, so you mean 1 year right?

That is probably an input shaft tooth, the knocking is broken pieces rattling around in there. So this tranny only lasted a few months longer than my last used 5 speed.

 

I thought I posted this a bit later after I got the car running, but yeah i suppose about a year. Regardless, i'm probably going with a drivetrain swap

However, I am running a lighten flywheel. Debating on going back to stock and car is primarily used as drift car. Usually when 5 speeds "blow up" I thought the gears themselves are the ones to shatter.

Is it possible the light flywheel vibration was the main killer rather then torque? Especially if was the input shaft that may of grenaded?

 

A heavier flywheel does reduce the shock load to the input shaft. In any gear other than 4th, in a Miata 5 speed, the input shaft gear transmits power to the secondary shaft. There is a gear machined on part of the input shaft, it seems to break in my car. I have always still been able to use 4th and sometimes the others with and without clunking past a missing tooth or several on the input shaft.

 

How exactly does a heavy flywheel reduce shock load?

The flywheel is part of the rotating assembly weight of the engine and stores kinetic energy.

Shock loads come from either the engine moving at a different speed than the driveline and the clutch is suddenly engaged, or it comes from the driveline suddenly changing resistance like losing then regaining traction suddenly from jumping a rumble strip for example.

In the first scenario, clutch kick or clutch drop, a heavier flywheel has stored more kinetic energy at a given RPM than a lightweight flywheel that it then must transmit through the transmission and driveline before the engine speed is reduced to match the speed of the driveline.

In the second scenario, suddenly losing and suddenly regaining traction, a heavier flywheel has also stored more kinetic energy at a given RPM than a lighter flywheel that has to be sent through the drivetrain before wheel speed matches actual speed.

At least that's how I think about it, I could be wrong though. I always thought that shock loads were best dealt with by using a sprung hub clutch disc, and engine/diff mounts that were firm but definitely no solid mounts or delrin there.

 

I mean you are right, but a heavier flywheel can store/absorb more energy over a lighten flywheel, and that energy has to go somewhere. It doesn't dissappear.

With less mass it can't dampen the vibration/load/shock going too the transmission .

Hense why you'll hear chattering coming from your trans when running a lighten flywheel.

 

You just answered your own question there.
The shock load I was referring to is the shock of a 75-100 horsepower cylinder firing, then 180° before another 75-100 horsepower firing. My trannies have always let go, in gear, not from engaging the clutch or wheel hop.

 

How are the 6 speeds holding up for you?

 

Let's just say, the jury is still out if they justify 5x the cost of a 5 speed in my opinion. If I can get another season out of it then maybe, if not then ZF. For my specific situation anyway.