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ACT Clutch Review - Blown and burned Clutch

ACT Clutch Review
This is the analysis of my blown clutch, and should serve as informational for those considering a similar setup to what I was running. This clutch was taken off my '91 Skyline GTR which at the time was running roughly 400 horse at the wheels.
ACT Clutch serial number
I got this clutch in a pinch last season from a buddy in Montreal, he'd used it for about 1,000 km's and then he had to pull his motor or something so he sold it to me, after a call in to ACT USA, I measured the puck thickness to be less than 0.10 of a mm different from new, and there was no glazing on the flywheel so it was in decent condition, this is a picture on the day I received it:
ACT Clutch unsprung puck and pressure plate
The clutch is stated for a 300ZX-TT but most people will also use it in the Skyline GTR because it's easy to get quickly and replacement disks are very cheap compared to other brand names. It's an ACT Ceramic 6 puck unsprung hub with a Toda Racing Light Weight Chromolly Flywheel.

As a review of how it felt to drive this clutch in my car, it has a very On/Off button feel, the ceramic tends to screech and whine when its cold, and it's not a very comfortable clutch for city traffic. How-ever, the lightness of the setup did make for a very notable improvement in engine response. The revs would rise and fall much much quicker than the oem set up. This clutch handled a few launches under my foot, with a little light feathering into a 4wd launch it hooks up very well and never slipped on me.
Burned lightweight flywheel
Burn marks showing through the backside of the Chromolly Flywheel
Two weeks ago from today, I was doing a launch just as I had always done before, a little feathering and a quick connect to jet the car forward, it hooked up nicer then I'd ever felt before. Up until now the car was running only 13 PSI for all of last season, so this was the first time I'd ever launched the car at my new power setting running 18 PSI since dyno-tuning. As I let out the clutch all felt normal, the car lunged up on all 4 wheels, and roared up the highway on-ramp tearing through first gear like a monster, at the top of first I pressed the clutch in quickly and went to shift into second to continue the glory that was this epic lift off which came to a sudden end. I couldn't get into second gear! or third! Something went wrong here....
Clutch taken apart - visible signs of damage to the disk and flywheel
I pulled over to the side of the road and was towed to Autoworx, where the car would undergo investigation. At first we suspected a blown Slave cylinder based on the symptoms, it made sense. But once the guys realized the slave was actuating fine, they had a look into the bell-housing only see shards of clutch everywhere, it was at this point we knew something went wrong with the clutch, so the transmission came out and what was found was quite interesting. As pictured above right away there were 2 noticeable brown marks completely burned through the flywheel.
Looking at the pressure the plate you can see signs of massive heat damage and something is actually stuck and fused onto opposite ends of the surface!
Here are some close up macro photos of the material which has fused to the surface of the metal pressure plate:
It's obvious to see whats happened here, the clutch disk must have gotten so hot that it fused material from the ceramic pucks onto the pressure plate. There are large chunks of clutch missing in the exact shape and position on the clutch disk. The material is also noticeably worn down completely to the rivets which is evidenced by the scoring on them.

The front side of the disk is pictured in the photos above, and we find the exact same markings and chunking off, on the reverse side of the disk as well.
On the Toda Flywheel it's the same story, massive burns and fused material...

In Conclusion: The guys at Autoworx believe the cause of all this unforgivable heat and fusion to be due to the combination of this clutch with a light weight chromolly flywheel. The thinner flywheel material and less heat dissipating properties of chromolly mean that when launching the car, the heat builds up very quickly and didn't have the chance to cool off, it became so hot that it caused the ceramic pucks to fuse with the flywheel and pressure plate. It's because they were stuck all together that I was not able to change gear.

I am happy with the use I got out of the ACT clutch kit, it sufficed for one season and put up with everything I threw at it. I guess the extra power and torque that the new tune has produced was just too much for it to handle, and it was probably close to the end of it's life anyways.

This story has been transmitted to Advance Clutch USA, and we'll be posting their response up here when it is available, I'm interested to see their take on this.
For the time being, I have replaced my setup with a new oem flywheel and a Stage 3 Bully Clutch. Bully is a Canadian company based out of Ottawa, so I was able to get the clutch for my car in less than a week. They also offer 90 day warranty which will cover my summer time use, and they've assured me it will be able to handle my car no problem. So far I can say the clutch feel is very light, and the heavier rotating mass is noticeable through a now slower engine response, but it holds the power well. Haven't had the chance to really drive it hard though as I'm still under the break in period for another 350 km's.


Anonymous said…
My suggestion would be to launch differently. When you're drag racing or hard-launching, you pretty much have to cut the clutch's torque rating in half. If you can avoid slipping or feathering the clutch on launch, then you won't have the over-heating problem.

To do boost launches on the 300ZX with a 6 puck clutch, we typically look to a traction/launch control system. This will let you floor the gas and build boost, without having to slip the clutch. I.e.


I slip my RPS clutch with a light weight flywheel and have never had a problem (550ft-lb 300ZX). I'm not AWD, but the car has pulled 60-ft times as low as 1.7 with drag slicks.

You might want to look at either a twin-disk clutch or a launch controller. I wouldn't expect any single disk to hold up to hard feathered launches. Especially a 6-puck, they aren't meant to be feathured.
Anonymous said…
PS, heavy clutches are also bad for syncros on RB26 & 300ZX trannys. You might notice you have trouble with high RPM shifts, especially with grinding going into 4th.

If you want to stick with a single disk because of cost, I'd suggest this light weight 5 puck. It will hold a crap load of torque, but just avoid excess slipping.


J L said…
Mike, great comment! Some things in what you said hint that you've got some first hand experiences with this stuff! Thanks man, I'm gonna lay off the hard launches for the time being lol
Sean Morris said…
Twin plate clutch up to about 600 hp. Then just go for the Tilton carbon/carbon triple plate. Its about $5k, but its butter.

1.7 on drag slicks? GT-R's will 1.6 on a street tire with a street setup. GT-R is heavier, higher RPM, lower torque. They kill clutches.

I know, I have killed a lot of clutches and transmissions.
J L said…
I'm nearly through my break-in period on the bully clutch now (350/500km) and its starting to feel quite nice! its very grabby and still 100% streetable, like you're saying though if this clutch gives up its ghost I'll have to make the move to a twin plate, any thoughts on the "spec" mini clutches? a lot of ppl recommend Exedy too.