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