After some searching here I didn't find any accounts of this issue happening to the Comp Clutch Stage II with unsprung full-face disc, so I'm posting this here for any ideas as to what happened to my clutch.

I am also curious to see if I can throw in a stock Evo disc or something with a sprung hub and keep this pressure plate. I know you can throw a stock 2G disc in DSMs with most aftermarket PP's and roll but not sure about the Evo's.

I purchased my clutch after reading reviews here: https://www.evolutionm.net/forums/ev...ch-option.html

Clutch has been in the car for around 10k miles, mostly weekend drives and short trips to the gym or out with the family. The car is mostly stock with full bolt-ons, HKS 272's and a 71HTA. Nobody will believe this but I have *never* launched the car from a stop. That's not to say I haven't taken off from a roll in 1st or 2nd, but I have never launched the car from a stop or dumped the clutch.

I am not using a clutch-stop, the clutch has always worked fine for me. No issues with clutch drag or disengagement point - everything is adjusted properly and was working normal.

The clutch failed when I was driving up a hill at around 35mph in 3rd gear. I was driving and suddenly the car was free-revving like it was in neutral, I had normal clutch pedal pressure and the transmission was able to go into gear like normal. The car just wasn't transferring engine power to the transmission. I figured I had stripped the input shaft or clutch disc but when I dropped the transmission I found out the inner hub had completely separated from the clutch disc. Pictures below:

This picture shows what I saw when I removed the transmission. You can see the inner hub of the clutch fell down in the PP after it slid off the input shaft when the transmission was removed.


Here's the rivets laying in the flywheel lip from where they sheared off of the clutch


Here's what the clutch disc looks like. Not sure if those holes are supposed to be slotted or not



Here's what the inner hub looks like. You can see where the rivets sheared off. Notice the splines are fine.



I've investigated around and can't find anything wrong with anything besides that clutch disc. I'm looking for any ideas as to what else I need to look at before I put the car back together with a new clutch. Also looking for info on what other "sprung" discs I can replace this one with because I'm not sure I want another solid hub disc. Thanks for looking!

 

Could it be from too much clutch engagement vibrations since disk is unsprung? Rivots can't handle the shock?

 

You would think the clutch is designed to handle the vibrations from a non-dampened hub, but that seems to be the case. My initial thoughts when it failed were that it would be stripped input shaft splines or clutch splines. I was surprised to see the rivets sheared off.

 

That's a failure that shouldn't happen uf it was designed and built right.

 

This is why you don't run solid hub clutches in street cars. I'm sure if you took the trans apart, you would the synchro stops are all beat up as well. This is caused from harmonics, as well as the the power pulses, sending shock through all the components when you're just cruising around and nothing is really loaded, and there's no sprung hub to absorb those pulses.

Check out @teamripengineering on instagram. He has the carnage caused by solid clutches pretty well documented.

 

Unsprung/Solid hub clutches are destroyed not at the track, but on the street due to severe traffic and the Toyota prius.

 

 

This is a good post & thanks for revealing the details

In regards to your question regarding the slotted holes. Pretty sure those holes are wallowed. You can see the witness marks where the slop was occurring.

Over time, those round holes wallowed & the rivets were getting hammered on & finally failed (just my opinion)

 

Wise words here, could be abnormal Sychro wear as well.

Couple solid hub with 271 cams causing even more unbalanced pulses into the clutch and transmission...

 

 

Hmm, that seems like an irregular failure. The exedy twin is a sprung disk clutch and should slip before taking out the flywheel ring bolts. Do you plan to run this new twin plate clutch in your 2.4l build? If you are making under 700ftlbs of torque at the crank, there are still sprung 6 pucks that can handle that power.

 

 

The exedy twin is a great clutch to daily on as well, I think you won't have a problem with it. For the budget build, there is always the ACT 6 puck sprung, it drives very nicely.

 

Well - I'm proud to say I'm a believer now! I was under the impression the solid disc clutches caused damage when launched and slam-shifting it. Considering I baby my Evo I figured I could avoid this kind of stuff. I'm glad the clutch disc failed before serious damage to the transmission. I am actually breaking the transmission down to inspect it and replace 2nd and 5th synchros so we will see if the rest of your words are true....

Looks like I learned a valuable lesson. Thanks for the input.

Thanks, I completely agree. Funny thing that it never made any more or less noise than it did from day one.

We will find out, won't we?

I appreciate all the responses from everyone and hope this experience can help someone out in the future.

Onto the next question.... can I throw any kind of Evo sprung clutch disc in? Like an OEM Mitsu disc or maybe a Southbend disc, or do I have to stick with a Comp Clutch disc? I know you could mix and match with DSMs but not sure if I can do that in the Evo.

 

Little bit of an update: I called Competition Clutch today to speak with them about it. After seeing the pics and how little wear there is on the clutch, they offered me a new full-face disc (sprung hub) for a discount and are also paying for return shipping for me to send them the failed clutch disc for analysis. Apparently this is the first they've seen of this in this type of car (mostly stock, no launching or racing, general street use) and would like to look into it further. Overall I am happy that they are trying to take care of me and letting me get a replacement disc at a discount. Their customer service was also on point.