afm

iTrader: (3)

afm

iTrader: (3)

I see in your video that your pilot bearing hole was too large, and that you used bearing retaining compound to hold it in.

A badly machined pilot bearing hole is pretty suspicious given that you're having weird resistance when the clutch is disengaged. It also looks like you installed it below flush, though that is probably less of an issue.

1993z32

The hole was a couple thousandths off, and both CM and a couple others with experience in the field recommended the retaining compound. Again with the trans in neutral a seized pilot bearing or malfunctioning clutch should not be causing the car to creep forward. Although, I am leaning towards ditching the clutch entirely at this point. As Savington mentioned it's the most reasonable cause for the problem thus far, despite not having any idea why it could cause such a problem.

concealer404

iTrader: (3)

I've never once, ever, on any car, for any reason, have had to use retaining compound on a pilot bearing, nor have i ever been told to do so.

And i've done a clutch or dozen in my time.

sixshooter

iTrader: (12)

I didn't know such a substance existed.

afm

iTrader: (3)

The tricky thing is that a single application of "unreasonable persuasion" can add a bent shift fork (and partial synchro engagement, and creep in neutral) to a different problem.

1993z32

Believable. But not seeing how that could cause the problem. I realize we're all theorizing here, but the more most reasonable explanations are going to help me choose my next move. If spending $1000 on another clutch + flywheel setup plus another $600 on a 6-speed is the most reasonable fine, but at the point that that 6-speed dies in 200 miles I'd hate to have wasted $1700. And after further research the BMW trans swap is $4300... and that doesn't include the differential or the transmission. I'm happy at 300whp until I can afford stronger drivetrain, which I still think is a reasonable power level for a street driven 6-speed.

By "unreasonable" I'm still talking less force than shifting quickly during a normal pull. More like a pull towards 2nd gear then shooting into first. With the car rolling at 1mph it should take a pinky finger to get it into 1st or 2nd.

concealer404

iTrader: (3)

Well. You have two broken 6 speeds, so you need another.

And you have a pilot bearing that didn't fit right, so what you do there is probably up to you.

Colipto

Good info that soothes my mind... Savington knows - Hopefully removing that clutch will resolve your issues.

I think most of us know what its like to take your time fixing something and then breakage

18psi

iTrader: (76)

I vote crappy or incorrectly installed clutch and or flywheel

fredb

iTrader: (1)

LukeG

Greg, do you have a Patreon account? You have a bunch of viewers at this point and I'm sure enough would pitch in to help you get this resolved. Hell, I've learned enough from your videos and enjoy them to the point where I'd pitch in $20 to help you get a new clutch/flywheel and trans. Get something reliable from Trackspeed or 949 this time. Those guys know their stuff and I'm very curious to see this get resolved.

Ryan_G

iTrader: (8)

You don't have to do the diff. You can just do the transmission swap for under $3k all in.

1993z32

And have ratios even shorter than the Miata 6-speed. If I'm spending thousands more dollars, I'm doing it proper.

Ryan_G

iTrader: (8)

They should be releasing the getrag 5 speed kit soon which would have very similar ratios.

DarkSwordsman

Two main things stick out to me.
1. You mention that in neutral with clutch engaged, it will try to roll forward as though it is pushing against a synchro. This is obviously transmission.
2. When it did fail, the car still was locked when the clutch was pushed in. This could be anything from the flywheel to the hubs, but if you can clarify that the diff is good and that the engine was still running when you clutched it, we can narrow it down to the transmission.

On top of that, you opened up the trans and it looked 100% fine, and the only thing was synchro dust.

To me, though you have a widely used shifter, I figure maybe it's too tall from the pivot point to where it meets the little cup that actually changes the gears (don't know what it's called). And as a result, it relaxes in a position where it is trying to go into a gear.

The only other thing is likely the clutch and trans not mating properly and the input shaft wreaking havoc on the internals.

VERY strange.

Edit: I read back through your symptoms. It absolutely has to be the shifter or linkage. The only thing that doesn't line up is the fact that it locked up, but I guess two or three gears could somehow both be engaged by accident and lock up the transmission (from the linkage being screwy) and then pop out and return to normal.

Perhaps the power does just pull things apart or move them around and just mess up everything. Is there a way to access the gears and shafts but leave a part of the housing off? I bet even if you lock up the output shaft and use a torque wrench somehow to apply 300+ ft lbs of torque to the input shaft, you can listen or see if anything weird happens.

Edit 2: I figure you could even cut a hole in one of the transmission to look, lol.

NiklasFalk

iTrader: (1)

Reading up (time zones...) makes me wonder. Would pressure applied to the input shaft (by to thick clutch assembly) have an effect?

I made the mistake once of not installing the pilot deep enough, which resulted in an engine not turning over, so a pressure hard enough to move the input shaft would probably have seen immediately.

omnislashx82

Honestly ive seen people put the clutch disc in backwards and it locks the clutch setup so that its engaging all the time. They get the movement while in neutral. Not saying you did that but it just makes me think the clutch setup is suspect.

kenzone

Hey Greg, I'm a fan.
More speculation here, maybe the overall engine vibrations at certain RPMs ranges are killing the transmission boxes?
You are running two clutch discs with no springs at all, although the one is fibrous, I doubt that is enough to dampen all the harmonics from the power waves.
So my take is that vibrations push the transmission internals to a state they shouldn't be, and bang.

Mount a sacrificial 5-speed to drive around and diagnose if the clutch itself has manufacturing/tolerance errors.
Until it dies, start collecting parts for a transmission swap! No no, not the BMW..

At your power level, a stronger transmission box is a must IMO.
There are known partial failures of the 6-speed at 390hp at the flywheel.
Although I believe you don't want to daily over 400whp power, it makes sense to have a better solution even at 300whp.

I would like to suggest an RX-7 box.
Turbo FC ribbed version for a notchy feeling or FD version for smoothness. I went with the FC version, but car isn't running yet so can't offer a first hand experience.
The turbo FC is what mattman runs, with a twin plate clutch. Hopefully your torque won't be able to kill it :P

Basically, I believe it's the most cost effective option for you.
In Greece it is a pretty common swap for high power miatas:

• You sacrifice a 5speed for a hybrid welded bell housing. Shifter remains where it originally was, and is compatible with the miata shifters, so you can retain your MR. You can use an adapter plate, but may end up being more expensive and pushes your shifter backwards.
• The transmission is plate mounted to the ppf or whatever other custom fabrication you prefer.
• You can use NC-6speed single clutch discs, or you get to keep your twin clutch and exchange the discs for 23teeth centers.
• The driveshaft needs to be cut and welded to an RX-7 spline. You may balance it DIY style to make sure it's smooth. You could buy a custom shaft.. but underneath the car is your natural habitat.
• You keep the miata starter/slave/bearings
• Turbo FC boxes go for around 150-200€, I expect them to be similarly priced there too.

My point is, for about the cost of another good 6-speed, you can have a known robust solution, as well as cheap enough replacements, should you end up destroying RX-7 transmissions which I doubt.

1993z32

Yes. All is was well for hundreds of miles prior to any issues. Also verified last night that pilot bearing depth is correct, the grease mark on the input shaft shows the bearing sitting right at the end of the shaft.

Verified both discs faced correctly. Also, neutral movement has been pinned on the trans itself, a soon as it exhibited symptoms in neutral/clutch out.

Update: Trans #2 is out. Inspected clutch/flywheel, everything looks fine, including the pilot bearing being in place and butter smooth. Trans itself is definitely jacked up. The only way I can see the clutch causing the problem is if the pilot bearing hole isn't perfectly centered which would cause vibration in the input shaft that I couldn't feel, and then somehow spawning unicorns inside the trans to rearrange the shift forks. I suppose at this point I'm going to try a different clutch and flywheel, and put my 5-speed back in, and none of the mysteries will be solved. Unless trans #1 miraculously seems fine after I put it back together, I suppose I'll try to run that.