This all sounds great and makes alot of sense, but I never had this high RPM lock out problem with the stock clutch. I would never miss a shift and the transmission went into gear everytime. I do not want to go back to the stock clutch again due to my plans for increased horsepower. If I were to switch to one of your Twin Disk Clutches, would my high RPM lock out problem be solved?

 

Tilton new clutch packages include a annular hydraulic release bearing assembly, designed to hook-up directly to the stock master cylinder with the include adapter fitting. The hydraulic release bearing converts the clutch to push-type, eliminates the mess of a external slave cylinder/linkage system, mounts directly into the transmission and self adjusts for clutch wear.

In addition, the Tilton units are lower inertia (not too low to cause drivabilty problems) that improves shifting. Tilton has a very proven (30+ years) reputation in racing and high performance applications, winning numerous race championships around the world each year.

I know of WRX/Supra/EVO owners that had problems with Exedy clutches not holding torque (non-carbon & carbon), and not had any problems with Tilton.

Tilton may not be a household name in the high-performance street market, but they sure have a excellent reputation in the demanding racing market.

 

It doesn't... But it makes for good advertising...
Sounds good in marketing terms, but from an engineering standpoint, I disagree.
First off, the clutch disc doesn't have to "come to a stop" but it has to slow to the speed of the next gear ratio. I don't think the disc weight is the "major demon" here.
Secondly, your two slightly smaller ceramic discs are probably much heavier than one organic, with no-doubt more inertia. And there has to be air gap on twice as many surfaces.
Finally, torque shock? While I agree that the springs will help reduce certain failures, they are primarilly there to reduce transmission noise caused from torsional vibrations. Nice pitch though. Solid hubs discs like our race discs or the Tilton have proven very reliable and not likely to break parts but certainly they can be easier on syncros. I think Jeff Hill's EVO and STI are good evidence of that. Just don't expect the trans to be quiet.

Some obvious questions:
Why does it happen on some cars and not on all cars?
Why does it happen at high rpms and not at lower rpms (even to a lesser degree)?
How many people haven't addressed adjusting the clutch correctly, have the release bearing installed incorrectly or had transmission issues to begin with?
Why does this happen on the EVO and not other cars with similar or heavier clutches and probably worse syncros?

There are a lot of cars with really crappy syncros that shift at high rpms with much heavier discs than the EVO. This seems to be a dynamic issue that is somewhat unique to the Mitsubishi. Honestly, I don't know if we can "fix" it, but I am confident that we can find the root cause. From experience with other 4G63s and some race Hondas with similar symptoms, I have strong suspicions about the cause or causes. I have a host of other questions that will be answered in time with some further testing and will let us know which suspicions are correct and what we can do about it.

For the record: I am not bagging on the Exedy Twin (race clutch) and I am not saying that the twin doesn't improve the shifting on the EVO. I just don't believe the issue is disc inertia. More on that later... after testing.

 

How would you know if you installed the release bearing incorrectly?

 

I haven't done an install on an EVO so I am only going by what I have heard by customers and seen in parts, but some symptoms are:

Will not shift very good at any rpm, even with extreme adjustment.
Lumpy clutch pedal (pulsation)
Vague pedal feel. It doesn't seem like a solid connection between your foot and the pressure plate because it isn't.
Broken release bearing or center components on pressure plate. The parts are usually loaded completely around. There is no reason for them to break unless they are unevenly loaded. This happens when the snap ring isn't snapped all the way in place.

 

^thanks for the run down on everything.
I had liked the ACT 6 puck...hell i even did my 11.3 pass using that clutch!

hope u guys get the problem sorted out because it's a good clutch at a good price

 

Did you have your tranny rebuilt and it still didn't shift at high rpm?

 

^no...i swapped the tranny altogether. I've got a spare evo engine and gearbox(basically like new)..
i was thinking it was the gearbox for sure. so I said what the hell..i've got a box on the ground doing nothing..let me put it in and see if it fixes the problem.

and it didnt....

 

that is pretty interesting, sounds like there is a problem that definitely needs to be addressed in the ACT...

 

If it is determined that this is an ACT issue with their product, are they going to incure the cost's to fix it for everyone? I just bought and installed my ACT HD pressure plate and disk, and I have not broken it in yet. Once it is broken in I will test it. If the same problem comes up, then that means ACT should have to fix it. Clutch installs are too expensive to have to front the money twice for a bad aftermarket product. I just hope I don't have this problem. Seems to me, a little more R&D should have been done. This won't be able to be passed on as all bad installs or bad Evo's! Just my $.02.

 

It's not just an ACT problem. I have a CM stage 3 and another a has centerforce clutch with the exact same problem.

 

so is it inherent in the single disc clutch design?

 

Yes this seems to be a problem with different clutch manufacturers. ACT seems to be a very popular clutch among Evo owners, that's why I think that the problem is showing up alot on the ACT's. When Shiv at Vishnu test drove my car after a tuning session, he mentioned that this is a problem with the single disk design. But I have heard of Exedy Twin Disk owners also complain of this issue. BTW, I got my Evo back from the guy who originally installed my clutch with the new clutch line without the restrictor in. The clutch feels so much better, but I did notice that they adjusted my clutch so that pedal is way up there. I looked under to take a look at the adjustment rod and there is hardly any thread left for any more adjustment. Also there is no clutch freeplay left either, I'm not sure that I like that. I was able to get the car to shift into each gear at high RPM, but there is still some resistance. I still can't shift as quick as I did with my stock clutch. The next step will be trying out the stock Mitsu transmission fliud to see if that will do anything. I will have to see if the guys at CenterForce will be willing to take a look at my car if the transmission fluid doesn't do the trick.

 

WHen you said hardly any thread left can you take a picture of it? Is it 1 or 2 thread left? I wonder how far is too far?

Thanks.

 

From my understanding, if you don't have any freeplay left, you've gone too far. That indicates that there may be some preload on the rod going into the clutch master cylinder which is not good. Mitsu specifies that there should be at least a couple of millimeters of freeplay left in your clutch pedal.