Exedy Twin Carbon Clutch Review
 

Just installed a used (300miles) Exedy ZM022SBMC1 Hyper Carbon twin disk clutch. The car is a single turbo, ~400whp, track/street car.

Install was typical for a clutch, nothing out of the ordinary other than the somewhat tedious job of stacking all the parts up on the center hub. Mostly it was a little annoying when some little parts keep slipping out of place. I used loctite on the front cover bolts because the Exedy USA tech guy recommended it.

Old (technology) VS New...37lbs vs. 25lbs
https://img160.imageshack.us/img160/...nclutch002.jpg
Just before the pressure plate and front cover go on.
https://img160.imageshack.us/img160/...nclutch003.jpg

Now for the driving!
Since I lost about 33% of my rotating weight and I don't know how to calculate the savings from a smaller diameter, but it must be significant enough because the throttle response is fast! Shifting was noticeably faster, hopefully with less wear on the synchros as well. Pedal modulation was easy enough, half clutch engagement was doable. I stalled it once after heating up the clutch a bit, engagement changes when it's hot because the carbon coef of friction increases.

I have high expectations for durability, my brother installed a 3 disc version of this clutch on a 800hp Evo. His personal observation was that the owner didn't know how to drive, and the kid still managed to get almost 20k miles before it needed to be rebuilt. Hope I can get 30k at least, especially since 2 discs cost about $1200

Overall I am very happy, but this is only the first day. Durability and track reports to follow.

Nice to see that you went with it. I'd like to drive a solid hub version of this once for a comparo. Perhaps the next time I go to Orlando...

Happy tracking.

I actually stationed in Omaha, NE. Florida is where I'm from/wish I was. I might have the car in the Chicago area this summer. I've been wanting to visit there with the wife, see the sights, eat the food.

Any good tracks close by? Know anyone with drag radials? If I found some of those to borrow for a pass I might even do a 1/4 mile again. My only goal at a dragstrip is to get kicked out. Sub-11 and no cage, I just want to run in the 11's once.

Updates :D?

^ Rich, just do it already :)

Hey brotha, I'm in Nebraska. I wish I could drive as much as you guys down south but the roads here are nasty. That being said, there have bee a couple decent enough days to drive the car to work, so I can give you a small update.


Pros - Easy (enough) to modulate, although definitely less friendly than a stock disc/ACT PP/stock flywheel, sorry but I haven't driven anything else to compare to. I think some of the reason the clutch seems easy enough from a start is that my car idles at ~1300rpm when it's warm as I've deactivated the IAS solenoid because it sucked. I think if your idle was lower it would be trickier. The motor revs way quicker, shifts faster due to less inertia on disc. Feels a little peppier down low too. Should hold the power just fine and last 30k miles plus. When you shut the car off it doesn't spin down like it used to, it just stops. Kinda odd but that what happens when you have 34% less rotating weight on your engine than stock.

Cons - With the clutch depressed it does make some minor rattling sounds, can't hear it over the exhaust (mine is obnoxious) anyway most of the time so not really a con. Oh, and discs are $1200 to replace. Haven't had very much slipping, it did once on the first day when I got on it a little too much but now it's broken more so it's holding fine.

Track report to follow sometime in early April, please be patient Rich. ;-)

BTW if you are looking for review for the sprung hub carbon-D some guys got a group buy from Ramy, I also think Rice racing has one. It was six months ago when the GB closed, so they should have them.

Although I sent him close to 3 VERY big bills 10 days ago for some Recaro seats and he hasn't even answered/replied to 2 simple questions, so maybe they don't have their clutches yet.

Well, I finally had a chance to run this clutch on the street some more and on the road course. I LOVE IT!

The throttle response is much better, shifting is faster, it is GREAT on the road course. It feels like there is more power down low. LOVE IT ON THE TRACK. Absolutely perfect.

Now the bad.
On the street engagement is OK and you can feather it most of the time. However it's a little grabby especially if it is warm like after a hard launch or 5 minutes of stop and go driving. You definately notice the difference when the thing is hot.
My biggest complaint is the gear chatter or chugging I guess you could call it. Without a sprung hub the car chugs around the RPM where the ECU picks up idle on deceleration. It bounces between fuel and no fuel in the ECU. There might be some tuning I could do to help fix this, or it might just be a fact of life with an unsprung hub clutch. We'll see how this affects the drivetrain as it can be a bit violent if I'm not careful.

It remains to be seen what the life will be of this clutch, but I'm holding out hope as my brother knew of one in Florida, a 3 disc on a 800hp Evo that lasted almost 20k miles with an idiot driver. I'm 1/2 the horsepower with 2/3's the disc, minus the idiot driver so I'm hoping for many more miles, maybe 40k?

Drag strip update.

Took it to the local 1/8 mile drag strip. I wanted to practice with the twin disk and new 275 width Drag Radials before I made the long haul to the 1/4 mile strip (3 hours away). Clutch held up great, no slipping w/ only a minor clutch warmup.

Best run of the night
7.549 @ 94.7 mph, 1.790 60'.
Mid 11's here I come!

Man that clutch is freaking pretty. It has that manly purple color LOL!

Sounds good Jon! Meant to call you yesterday to see how it went.
Any trick to figuring out how to launch?

Nope, I just did a couple half pedal blips of the clutch at 3k while I was rolling out to the water box, that put enough heat in the clutch to grab off the line. Then it was my normal 6k launch and feather. 1.790 60' on drag radials isn't great, but it isn't terrible either. I bogged pretty terrible on my first launch, but after that I think 4 of 8 runs were 7.7X @ 92-94mph with .07 to .15 R/T. That's pretty consistent I think!

so how long has this clutch lasted??

I just got a used one and I need to get those carbon disc...lol

That's a really interesting and cool setup you have. It sounds like the results were similar to my kevlar clutch, although it was single plate.

Just as a warning to someone considering purchasing a kevlar clutch, they are very sensitive to heat. Much worse than an organic clutch. If you slip the clutch at all, even a little, it instantly loses grip. They are extremely strong and durable because of the kevlar material, but you can't ride the clutch one bit. I'm assuming the carbon discs in your setup do not have this problem.
The other issue with kevlar is the break-in time. It took over 500 miles before the clutch broke in and stopped slipping. When it was breaking in if I ever let the boost go over maybe 7 lbs it would just slip. So to break it in I had to just drive around town from stoplight to stoplight just driving normally until I had 500 miles on the clock.

Had it for about 8k miles now, still running great!

And it doesn't sound like your Kevlar clutch is anything like mine. Carbons coefficient of friction INCREASES when it gets hot, which is what you want in a clutch. A material that slips worse when it heats up sounds like a terrible idea.

As far as the replacement disc, hope you've got a full bank account, those discs aren't cheap. Give the US Exedy tech support folks a call, they can hook you up with the right part number and where to order it from.

Yeah the part number is DP03 (drvn plate). I think this is where having a business is really going to pay off. I do not know what my cost is on those discs but its cheaper then retail. I'll see if I can get them cheaper using my discount of going through the guy who is sponsored by them since he gets this set-up for FREE!!!!!!!!! ..lol

Either way, I am not even tripping off of buying the disc since I got the used one for free too. I just need to resurface the 4 faces and get 2 discs and I'm good to go.

I'm really happy that I got this, and since my car will be only driving 5k to 7k miles a year this thing should last a long time.

Glad to hear it’s still going strong for you.

The drifter I got it from makes around 450 whp, and he beat the shit out of it for over 2 years and the clutch didn’t really go out, it just started slipping at the top of 3rd gear. When we took it apart, all the metal surfaces had some crazy heat marks and discoloration. It looked like someone took a torch to it and just heated round burn marks everywhere .lol

The discs however were just thinner but not deformed or burnt at all. No scratches, cracks or any discoloration. The discs were solid as shit and were not fraying at the edges. Even where the disc fit into the center spindle (those square/rectangular grooves) was solid with no nicks or chips.

So, the disc beat the shit out of the metal mating surface. So for anyone who has this clutch, the carbon disc breaking would be the very last of your worries.

Based on what I saw, this is not a clutch you want to slip because as fitzrx7 states the hotter the discs get the more they grab. You don’t want to be popping it either. This is definitely a clutch that takes getting used to, but also this thing will out last any other clutch in a race/track/drift environment.

Come to think of it, I'll post some pics of what these discs do to the metal so you can see these things are no joke.

Also we installed the new one and it said the flywheel bolts are torqued low like at 48 to 51lbs or something like that; we did it to 71lbs.

For the pressure plate we torqued to the recommended 23lbs but used thread lock to be safe.

When he drove it he had a big grin on his face, it grabbed like hell.
Ben

Heres those pics, 2 years of constant abuse and it just starting slipping. It's amazing it still grabbed.

Holy shit that got hot!! Those discs definately have some serious wear, the slots are worn off. You should measure those with a micrometer because I think they they are probably below the allowable wear limits. I'd love to know at what level they start slipping at. I don't have those wear specs with me as I'm posting this from FL340, thanks Delta for the free wifi onboard!

Thats what it took for it to start slipping in 3rd gear with a FD that makes 450 whp.

This was out of Calvin Wan's drift/time attack FD so you know this shit was abused properly, by a pro...lol

Well, some interesting news on the reliability front. I just got done replacing one of the discs as it had worn to below allowable limits in approximately 12k miles of driving.

I bought the clutch used and the thinest disc was at 4.11mm, down from 4.2mm brand new. They are allowed to wear to 3.3mm before they must be replaced. When I took the clutch apart this time the outer disc was at 3.0 mm while the inner disc was at 4.0mm. After talking with an Exedy USA tech person they recommended swapping the discs every 3-4 EVENTS because the outer disc wears more rapidly. Needless to say that is going to get a little frustrating, but it's either that or buy a $620 disc every 12k miles. Overall, still really happy with the clutch, it's awesome on the road course.

Thank you for the update. I guess I will have to look out for this problem as well as I have the same clutch.

What made you decide to take the clutch out? slipping?

Also, do you know if this is an inherent problem with a twin disc design or is there some sort of flaw in exedy's design causing premature wear on the rear disc?


John

I'm sorry for the uneducated question, but when it comes to multi-disc clutches I have no idea. I usually stick to a Spec Stage 3 clutch with sprung hub and it does the trick for me. What are the advantages of a multi-disc clutches?

^ You have more friction area therefore you can hold more power. In addition if you have a single and a multiple disc clutch both rated for the same input torque, generaly the multiple disc clutch will have a lower clutch pedal effort. Multiple disc clutches also allow the use of a smaller diameter clutch disc and pressure plate. This lowers the inerta of the clutch setup freeing up some horsepower.


John

^thanks, I'm guessing pedal effort is less too?

^ Yes




John

Thanks for the lesson John

The engagement point had slowly changed, which was partially due to wear on the drive lugs that mount to the flywheel and partly due to the worn disc.

The front disc wearing more is an inherent problem with a twin disc, and it is compounded by carbon's increasing coefficient of friction when it heats up. So the front disc sees more pressure sooner, so it heats up first and holds most of the load when you don't do the "warmup procedure". If this was used only at the racetrack and only driven after the "Warmup procedure" then you most likely wouldn't see as bad of a wear difference between the two discs.

At least that was the impression I got from the Exedy tech guy.

Fitz

Any updates wrt to longevity, track performance etc?

I know that they recommend switching the disc back and forth on drift/track cars every few events.

I know that Calvin Wan (you can see the pics I posted) used his set-up for a few seasons (heavily abused) and in the condition in the pics it started slipping in 3rd but he was making a little over 400whp on a decent single turbo.

I think this is a good investment for a weekend warrior. You can probably swap the disc every 10k miles to make it last.

EDIT!!!!!

I know that they recommend switching the disc back and forth on drift/track cars every few events.

I know that Calvin Wan (you can see the pics I posted) used his set-up for a few seasons (heavily abused) and in the condition in the pics it started slipping in 3rd but he was making over 400whp on a decent single turbo.

I think this is a good investment for a weekend warrior. You can probably swap the disc every 10k miles to make it last.

Im going to measure mine to see where they are at. Like I said, the disc started slipping in 3rd in their current condition. Who knows how much the worn and un-even surface of the pressure plate and intermidiate plate have to do with this.

I am going to have the cnc shop machine it smoth and throw it in with the worn disc and just see what this clutch can do with this much abuse on the disc.

So basically it has exceeded all specs for minimal wear, lets see if itll hold 300whp on twins....when I get my car running...lol

Would be interested to know what those disks are at compared to min spec.

Interesting that that setup is so resilient.

Wondering if the main damage to the plate is from the recent slippage?

Yes please could you take a quick measurement of the disks?

Would be interesting to see where they really start to give out.

The Exedy catalog is notoriously complicated and ambiguous IMO..... evidently there is a Comp-D twin disc which is similar to what I'm currently running (cerametallic six puck discs) but is about 5 pounds lighter (25 vs 30). I don't want the carbon discs due to this whole 'swap out every few track days' things as well as some info I've heard that the carbon unit doesnt really hold past about 450 rwhp in a rotary.

Luckily I was able to source a new Comp-D from a buddy and it's being shipped to my place soon :)

I forgot to do it today, Ill hit it up tomorrow morning, I'll weigh the unit I have also.

Goodfella, so you got a Comp-D twin disc? Is the price simular to the exedy twin carbon disc?

^I guess we will find out:).


Why is it only recommended for the clutch with the carbon discs to be swapped every few track days? The carbon and the ceramalitic clutches (not discs) are the same mechanical design (the way the pressure plates work), from what I can tell.

^ NVM, Re-read the thread and the question was answered:blush:.

I'm going with ZM022SDL which is what Exedy recommended for my use. They will chatter a little but weight is less than 6lb compare to ZM022SD. ZM022SDL is currently not available and need to be ordered from Japan. I was told Exedy USA has 4 Carbon twin disc clutches available. But those should be used in track purpose car vs. street. I was told carbon twin disc are 2-3lbs lighter than ZM022SDL or almost 9lbs lighter than ZM022SD.

going to weigh and measure my kit now, ill have some info in a bit

For some reason I dont know how to carry my pics over.

Here is what I found out.

My clutch part number ZM022SBMC1

The single sided top clutch plate is 5.00 mm thick. It showed wear anywhere from 0.15mm to 0.20mm
The dual sided clutch plate is 5.35MM thick (0.35MM thicker then the single sided plate) and had the same wear on both sides from 0.15mm to 0.20mm.
The flywheel was scared but mostly flush and not worn down.

Disc #1 was 2.66mm average with a varience of +/- 0.10mm at random checks around the disc
Disc #2 was 2.50mm avearge with a varience of +/- 0.10mm at random checks around the disc

I weighed it at fed-ex on their postage scale, mine comes in at 21.76 including all the bolts, yes with the flywheel bolts too.

Here is what I noticed.

Every single surface the the disc touched it looked as though they were worn at a slight angle. The burn marks were bad but the plate did not have alot of material missing.

I believe the presure plate has come lose or was not torqued all the way or under/over torqued on some bolts more then others. Thread lock was not used.

This would explain the angle of wear on the metal and the radom reading on the carbon disc.

The disc were traying to grab at an angle of 0.10mm to 0.20mm due to uneven torque.

Thats my guess, so as beat up as these things were and given that the presure plate was not evenly torqued and as a matter of fact losing presure due to the disc getting thinner I'd say slipping at top of 3rd on a 400whp drift car during an event is not to shabby.

Im just going to have the cnc shop resurface it all and throw it in and see what it can do in its current condition.

What do I have to lose, I got htis used unit for free and everyone can benefit to see just how far down it can go and still work.

Ben

I think based on what I just found out, I would just keep tabs on the torque.

Calvins disc were at 2.66 and 2.50 which is far below 3.3 "the cut off from exedy" and really below your 3.0.

It sucks that you had such a big difference between your 2 disc.

Ben

Thank you!

And thanks for experimenting with the disk also, will be interesting to see just how far it could go.

I am wondering if the combination of a worn disk and a resurface will be too much for it however?

Is there a chance the pedestals could be shortened to accommodate the change in thickness?

And assuming new disks put back in spacers to bring it back out to original specs?

OMG!

I didnt even think of that, I guess that would be critical.

As far as the resurface goes, the plates are bearly cut into, they are just super burnt...lol I can probably get away with just sanding for some of them.

They pedestals can be unbolted, I'll just have the cnc shop make some shorter ones...lol.

As it sits right now I still have a gap even with everything worn down as much as it is. I'll try to torque it to spec and see whats left.

If both disc are 4.2 new, thats 8.4mm

Im around 5.20 combined. Then the wear on the plates combined is like .40 or so.

So Im like 3mm down from new.

Ill re-surafce everything and make new pedestals 3mm or so shorter then they are now.

This way when I rebuild the kit I have the original stuff.

The only sucky part about this whole thing is my car wont be running until the end of the year.... :(:(

Who here among us hasn't played that game before?

I am just interested incase I ever have to deal with the issue, my guess is I will not have to, but who knows its one of those things I thought about when purchasing, and has piqued my interest that it may get answered.

Please take the time to update when appropriate!

I think everyone will benifit and pull these back out the closet if it does pull some decent numbers.

Maybe there will be a need for a "2nd life pedestal kit" hahahahhaha



In a previous statement:
If both disc are 4.2 new, thats 8.4mm

Im around 5.20 combined. Then the wear on the plates combined is like .40 or so.

So Im like 3mm down from new.

I added the wrong way..lol

8.4 disc thickness
5.2 combined
loss of 3.2mm
loss on all the plates is around 0.40

Total loss is 3.6mm so thats closer to 4 then 3...sheesh.

Looks like after smoothing everything out I should take the pedestals down to 3.8 to 4 mm to get the same pressure as new without bottoming out like it would now. Taking into consideration the loss if any of the splines on the PP.

What do you guys think?

Here is a related question..

Anyone runnign the carbon variants of this clutch or others, what is your throwout bearing life expectancy?

Just checking mine, and compared to a old one using a stock clutch with many miles on it, the new one with very little mileage on it feels crunchy and binding when rotated.

What can you say about the throw out bearing?
Very interested to here what others have to say on this topic!

Wow, tons of stuff since I last checked in!

Ben, lots of good info there man, thanks! The concept behind taking the drive lugs down 3.8-4mm sounds workable in theory, I would just worry about the resiliency of the carbon discs being that thin, as well as the replacement costs of the drive lugs when you have to finally get new carbon discs. The good news is that (I'm guessing here) if/when the disc(s) decided to break apart that they would shred up and disintegrate without too much damage to the rest of the clutch components.

Also, thanks for the wear info on the discs that you have. I think the even wear of those is due to the constant heat that clutch experienced in a full-blown race car versus what my clutch sees with a mix of track and street use. I'm fairly confident my uneven wear was due to the street miles on my setup. Like Herblenny said, I think this is why Exedy recommends against using them in street cars.

Good info, thanks guys!

Im going to make new cncd pedastals so all I have to do is swap the old ones back in when I get new disc. :nod:

Anymore updates,thoughts 2yrs later?

I've got the cerametallic twin disc. It's by far the nicest clutch I've ever felt. I have a few experienced buddies who've driven the car as well, and they've said the same. It's like the perfect amount of give with all the hold I'll ever need.

I still am using my car to build vmount kits on and as soon as im done im going to throw it all together and make the new pedestals for the clutch. I do not have much experience with this clutch so ill have Clavin test drive it for me and get his thoughts.

OP sold his car a few months ago.

I've been thinking of buying one of these but with a 10k mile life span and $1000 for replacement disk doesn't seem reasonable.