thumpetto007

iTrader: (15)

Im gunna go out on a limb here...

1 you used a clutch that isnt recommended or built for a miata. (Told you so on youtube mannnn) measure the thickness and conpare it to stock clutch, maybe you need a bellhousing shim or something. (Not sure what is necessary in this case, other than buy a quality clutch that everyone knows works without issues from 949 racing)

2. You tried forcing the shift lever, at least one time, into gear, and bent a shift selector, linkage...

1993z32

Not saying the clutch isn't the problem, but for arguments sake if I were to space the bellhousing off the engine, the input shaft would not go all the way into the pilot bearing. I already verified that the pilot bearing does sit in the exact factory location as far as fore/aft position.

I'm leaning towards buying a 949 setup and starting fresh.

concealer404

iTrader: (3)

I have Y8S's twindisc setup if you want to save some dollars and give me some shelf space back. I got a smaller Quartermaster/Prather setup i'm going to use, and binned my turbo project so i don't need anything as strong as the Tilton.

huesmann

iTrader: (1)

I guess when the trans is busted and you're not putting it back together, there's no reason to disassemble it in an organized fashion!

Arca_ex

iTrader: (2)

If you're talking about the Quartermaster 5.5" twin disk, the strength comment is funny. They're rated to 600 ft/lbs.

That's the setup I run. Great for the track, sucks huge ***** at everything else.

concealer404

iTrader: (3)

I'm super excited then.

Don't really care. It's lighter than the Tilton setup, and ease of driveability is less important to me in an n/a car than a turbo car.

wackbards

iTrader: (2)

What's the health of your clutch hydraulics like? I'm curious whether the slave cyl might have **** out, or can't cope with your clutch. Just trying to eliminate the obvious here.

1993z32

Update: 949 Twin Disc purchased, currently hunting for 6-speed number 3

der_vierte

Hey greg,

first of all: i love your videos and watch every episode.

To the 6-speeds and clutches: I remember a guy here with a nearly as strong setup as you, who came from a FM2 clutch (full face sprung) to a 949 Twin Disc clutch
and he broke his gearbox in 2 weeks. He said, he now only uses sprung clutches for keeping the gearbox alive.
Not saying, that the 949 clutch isnt any good, it sure is, but maybe those light weight twin discs tend to brake gearboxes just a bit earlier...

As you said, we all know that we are pushing our luck with that kind of powerlevels and the stock miata components, but two broken ones in two weeks is just too much.

I really hope it's a clutch related problem

aidandj

iTrader: (5)

phocup

Might be way too far for you but I have a 6 spd fs in San Jose.

_integrity

Greg, you contribute a lot of awesome material for the Miata community. Some personal thought's based on your problem description:

Symptoms -
1) Will not go into any gear without unreasonable persuasion. Normally a clutch fault but when in gear, clutch has at least 1-2" of travel off the floor until the car budges. -I think that this is the first/best thing to keep in mind when I read through the problem description. When the trans was say even on the ground when you first got them were they fairly easy to move into gear?
2) Trans in neutral, not touching the clutch - car tries to roll forward and sometimes even kills the engine from so much resistance in the trans. It acts as if I'm pushing really hard on the shifter and the friction of the synchro is pushing the car forwards. -Sounds like internal components are bound.
3) Following along with #2, if I'm rolling 60mph, and put the trans in neutral + release the clutch, revs will come up to 2-3000 and car will slow down. Again like I'm pushing really hard on the shifter against a synchro. -Same as above
4) Rear wheels fully lock up while car is in motion (luckily 15-20mph both times) even with clutch depressed. Usually followed by some sort of loud bang and the wheels free up again. -Teeth getting stuck and ejected?
5) HERE'S THE KICKER. First 6-speed, when I got the wheel lock, trans goes back to normal and I drive it home like nothing happened. -Stuck components broke free potentially
When I drained trans #1, it was full of gold synchro dust. -Quite possible if shifting without the clutch functioning 100% and it's trying to make it in gear with resistance of a non fully depressed clutch.

My theory is that the transmissions are having true mechanical failures, synchro dust & loud bangs are never good. Some of the symptoms could happen with differential failure however the one a few that stands out is the car moving forward in neutral. I would measure the new clutch versus the old and see if there are any differences before you lose the chance to once you install the 949 Unit.

Best of luck.

mrryanbaker

iTrader: (11)

Foooor sure. I have one sitting on my workbench that I don't know if I want to install because the Exocet occasionally sees stop and go traffic.

Arca_ex

iTrader: (2)

I would leave it right where it is until you have a trailered track car to put it in. Stop and go traffic will kill it awfully fast.

1993z32

I have completed disassembly down to the core of the failure. See pics below and as well as my theory at the bottom as to what I think could have caused it to happen.

First, let's have a look at the countershaft. This houses the selector for 3rd and 4th gear only. Anatomy outlined below.



Below is also the countershaft but with the gear selector sleeve removed so you can see the hub. Important note: there's supposed to be a specific distance between purple and yellow, so that 4th gear is free floating.

This appears to be the failure. The synchro has slid off 4th gear slightly, causing it to bind with the hub, and therefor the countershaft, causing the car to pull forward in neutral.

This is what it looks like after being tapped into place:

Unfortunately once the ring had been dislodged from its home, the damage occurs quickly, note the heat ring from the friction as well as the lip that would hold the synchro ring on the gear:

As well as the 4th gear side of the hub with lovely gouged out surfaces:


So, with my new in-depth understanding of what's held in place with clips and what's actually able to move around inside our 6-speed boxes, I present the ONLY theory that makes any sense to me:

Edited out nonsense.

Edit - plausible scenario: The selector sleeve has a death grip holding the toothed synchro to the hub (while in 4th). The torque (or a hard shift, especially without the damping of a spring hub clutch...) then pulls 4th gear off the synchro (the steel ring, not bronze) due to the direction of the helical cut. This theory also coincides with the 4th gear mis-alignment failures I've heard of. I guess long story short, if you're pushing mad JDM power through your 6-speed, 4th gear is the one to take it easy on.

Arca_ex

iTrader: (2)

In the first picture there, what's the direction of rotation of the countershaft while the car is moving forward, and which end is towards the engine? If it's moving the way I think it is, big power is putting a huge load on the gear in the direction of the shaft itself, it's a downfall of helical gear sets and it may just be tearing itself apart.

My initial thought is that the shift fork is more prone to bending before you could actually apply enough force to separate the gear and the syncro from each other like that.

aidandj

iTrader: (5)

Probably should get a track car first...

1993z32

+1 and +1.
Re: the helical gears - once Savington explained that the 6-speed has an issue with misaligning 4th gear under power it all started to make sense after really digging into the trans and finding the exact cause of the damage. Although I wasn't super hard on the 2nd trans, I did do a few pulls, albeit at lower boost, and maybe I just got real unlucky. And I did verify that under load, 4th gear does want to pull away from the hub/synchro.

Re: the shift fork - Since the shift fork would actually be pushing the ring back into place, there's no way it could be dislodging it on a hard shift. However, I don't think the forks would be strong enough to slide 4th gear on it's splines anyways.

thumpetto007

iTrader: (15)

Eyyyyyyyyy what do you know.... A torque related failure....

NiklasFalk

iTrader: (1)

So another vote for lowering the final gear and only have full torque in 5th (lowering the final gear to spend more time in 5th than before).
Kia 4.77 and 6sp is a good track choice, but not the nicest on the street .