my spec stage 3 clutch that is rated to 550 ft.lbs slipped when i was racing a z06 today. im making no where near 550 ft/lbs. it will grab at 4500 rpms, but not anything above that. i also have a ss clutch line and removed restrictor. any ideas why this clutch is doing this? im pissed, i was only able to hang at the door of the z06 because of it .

 

clutch master? most spec stage 3 clutches use kevlar, which last very long but doesnt grap like organic or ceramic materials, they require alot of clamping force to grab usualy 60-75% more clamping force. clutch masters uses about 45-50% i believe which to me isnt enough clamping force for a kevlar faces disc. also clutch master throw out bearings are crap.

how long have u had the clutch, if its new give it alittle time and be easy on it, break it in a bit, sometimes over a short time theyll star to grab, but for awd applications, id stay away from stage 3- kevlar clutches.

 

i could have sworn it was organic, but your making sence. it takes every abuse and it never smells. will it hold up to 550 ft lbs? because i will be making near there soon. maybe it wont tear up my tranny as soon. i dunno, it may be a good thing. i like auto crossing alot better than dragging, and it shift Quick and crisp.. maybe i should stick to that.

 

im sorry your having this trouble. i know u spent alot of money for the parts and perhaps labor.

most clutch companies offer about a 45-55%increase in clamping force with these kevlar clutches which is about the max they can increase the clamp force from the stock pressure plate, this is achieved by changing the pivot point on the belville spring. some even heat treat them.

this works fine for 2wd applications which is why so many hondas run stage 3's but the kevlar just wont grab with the traction from an awd vehicle, in order to run a kevlar disc you would need at the very minimum a 60% increase and i recomend 70% in clamping force.

this requires a purpose built pressure plate with a cnc'd spring (ex. act extreme pressure plate).

for now i suggest anyone upgrading there clutch to use a modified stock pressure plate and a six puck ceramic material disc (usualy given a stage 4 rating), in a single disc clutch they can be very grabby which can lead to driveline failure. however i have seen some that are slippable...but not yet with the evo. ive had great luck using clutchnet's products. i dont believe they have a clutch for the evo but im sure they can make one no problem.

next option is mutli disc clutches, they are too usualy ceramic but because they engage more progressively, they will slip and engage much more smoothly. however the cost is much more great.

i think we just need to keep an ear out and find a good single stage clutch that works well for the evo. for higher output motors a ceramic disc with a purpose built pressure plate should work fine or a dual disc setup.

 

if your disc looks liek this its a kevlar disc
was i right about clutch master, if i was then i know its kevlar
Clutch Masters Stage 3 EVO VIII

when clutch manufacturers test clutches they bolt them up to a table or test bench. they insert a dummy input shaft and put a huge toque wrench on it. they turn the torque wrench till the clutch slips, the torque measured just before the slip is its holding capacity. make sense, sound accurate?

well get this

in real world, the car is running, your constalty engaging and disengaging the clutch
produces heat, heat changes the coeficient of friction.

see the delema?
i guess kevlar just doesnt have as good a coeficient of friction as the other materials

im placing this all on my experiences and what i do know about clutches.

 

is twin disc more slippable than the stock?

 

no the stock unit is very slippable

 

i acutally have a "spec" clutch, and it has an aftermarket pressure plate. it may be a remake of the stock one im not sure. is this what they do to increase the clamping force?

 

i have a CM stge 4 it has bronze in it....and i love it ..talk about no slip ....the chatter sux though on 1st....but w/e we do drive race cars and not bmw's

 

they modify the stock pressure plate for light duty clutches, they make custom belville springs, that are thicker and heat treat them for heavier duty aplications ie. purpose built pressure plate.

i have no experience with "spec" nor have i heard of them, i couldnt offer you any advice, i hope it works out for you though

 

i have the heavy duty pressure plate too

 

cm stage 3, 9 months, no slipping........

-shu

 

Actually, you are right and wrong. First of all, most performance clutch manufacturers don't do any testing but simply make up numbers to make their clutches sound good (oops, did I say that?). A torque wrench would be far too technical for them. You've seen the ads... 200, 300, 400% increase over stock with stock pedal feel (or whatever sales pitch). Yeah right! You know the saying: If it sounds too good to be true...

The manufacturers that give FACTUAL numbers will calculate what they know about friction values and clamp loads and simply calculate the torque capacity. At ACT we have verified these results on the dyno and on the track. We use dynamic torque values (slipping torque) when we mention torque capacity in our literature, we calculate our values using peak clamp load. Keep in mind that a pressure plate is not necessarily installed at peak clamp load however. It is important therefore for us to design the clutch in the properly working range for maximum torque capacity and wear. The problem is that the testing can be done or interpreted in so many ways that it is almost useless to compare figures of different manufacturers.

You are right to think that static torque is much higher than slipping torque. Let me illustrate this. John Shepherd gets away with a street clutch setup and still runs deep in the 8's (1/4 mile). I ran the calculations myself on what that clutch should hold and it comes up about 100 ftlbs shy of what the car is making! Since the DSM has such a fragile driveline, John can't simply squeeze it off the line and hammer the gears. If you see his runs, he shifts very smooth and engages the clutch all the way before applying full power (around 900hp) so the driveline will live. John has become so used to his street setup that he doesn't want to change to our race setup. Humm, it occurs to me that the clutch John runs on his DSM is the same friction material and similar clamp load we offer for the EVO, but the EVO clutch is bigger, beefier and has more surface area.

BTW: Kevlar is great for bullet proof vests.

 

For me the stock clutch holds very well after full engagement, I just want something more slippable when I launch at traffic light. I could get it to launch quick slipping at 4000rpm but it will smell burnt. I don't want to dump the clutch at 5000rpm at every traffic light, so I need something that could be slip-launched.
Appearently noone makes that clutch.

 

I thought I was the only one . My CM Stage 3 is on its way out as well. Installed November, put about 6k on it. Next up for me is the Cusco twin carbon/carbon