Technical reasons for Evo clutch failures
Sep 22, 2003, 10:31 AM
#1
Technical reasons for Evo clutch failures
To this day, I haven't "launched" this car. I drag raced my WRX like crazy, but I'm exercising restraint on this until we can at least understand the issue better.
I know there is a strong contingent of people that think this is all driver and abuse related. However, while I will concede that slipping the clutch at high rpm will certainly exacerbate the coming of its demise, I still think the amount of failures is abnormally high in proportion to other car models- specifically the WRX and the STi. Looking at any pool of data, you're going to have the full gamut of driving styles in all three ownership bases. Specifically, I mean that there are WRX and STi guys that drive exactly the same way lots of Evo guys do, but you still never see a clutch failure at stock power levels in Subaruland. That's a very hard piece of data that is worth taking a closer look into, IMO.
From everything I've read on EvoM, I think Dirk from ACT has thrown out all best ideas. He does this professionally, and has seen more clutches in his life than everyone of the rest of us combined.
Some very interesting facts we have learned in review before we start hypothesizing further..
(1) The clutch disc material is the same used in several other cars, including other turbo+AWD cars, and has not failed as completely or as quickly as in the Evo.
(2) In examining obliterated discs, it is interesting to note that the pressure plate is still performing correctly, and almost 100% of its torque rating remains when tested.
(3) Evos overseas are not seeing this problem anywhere near as much as we are per capita/per car. This might be our obsession with drag racing, or it could mean there was a defective run on discs here, but I really think the former makes the most sense.
From reading and watching these cars launch, I think the failures are a combination of things. I'll list what I think the worst offenders are, starting with the most damaging to the stock clutch.
(1) The slave cylinder restricter. Obviously, this little guy is designed to make the clutch slip and protect the tranny. You launch the car at RPM, you can guarantee a thorough clutch roasting.
(2) First gear is too long. As short as the gearing is in this car, first sure is tall! It is 40mph capable at stock redline. Both Subarus are well into second gear at this speed. Slip/dumping into a tall first gear is very hard on an AWD car's clutch.
(3) Sticky tires with big 235 section width. Not a lot of room to spin the tires too much there at all. Hence extreme clutch disc burning.
(4) Two foot rubber clutch line from master cylinder. IMO, this one is sketchy at best. The pressure plate has already proven to work well, and when I switched, I felt a slight improvement in feel, but does the OEM piece balloon enough to make the pressure plate not function at 100%? I really doubt it. I've **never** smelled burning clutch in this car (probably because I haven't launched it), and even at WOT full lift and back on upshifts, my stock clutch has performed perfectly. Twice since I've owned this car I've grinded second gear. Once before replacing the clutch line, and once after. I don't think the line effects the response time of the pressure plate. Something like that would have never made it past Mitsu quality control.
Well, my car got the restricter pulled and the SS line at 800 miles. Those are #1 and a distant #4 on my list, and I'm wondering if anyone on here has had a clutch failure with the restricter pulled?
I think #2 and #3 deserve more attention than they are currently receiving, especially #2. These will bear out moreso if failures keep occuring even with aftermarket units. Right now, the only seemingly sure-fire way to make this clutch last is to not launch the car.
Input is welcome.
I know there is a strong contingent of people that think this is all driver and abuse related. However, while I will concede that slipping the clutch at high rpm will certainly exacerbate the coming of its demise, I still think the amount of failures is abnormally high in proportion to other car models- specifically the WRX and the STi. Looking at any pool of data, you're going to have the full gamut of driving styles in all three ownership bases. Specifically, I mean that there are WRX and STi guys that drive exactly the same way lots of Evo guys do, but you still never see a clutch failure at stock power levels in Subaruland. That's a very hard piece of data that is worth taking a closer look into, IMO.
From everything I've read on EvoM, I think Dirk from ACT has thrown out all best ideas. He does this professionally, and has seen more clutches in his life than everyone of the rest of us combined.
Some very interesting facts we have learned in review before we start hypothesizing further..
(1) The clutch disc material is the same used in several other cars, including other turbo+AWD cars, and has not failed as completely or as quickly as in the Evo.
(2) In examining obliterated discs, it is interesting to note that the pressure plate is still performing correctly, and almost 100% of its torque rating remains when tested.
(3) Evos overseas are not seeing this problem anywhere near as much as we are per capita/per car. This might be our obsession with drag racing, or it could mean there was a defective run on discs here, but I really think the former makes the most sense.
From reading and watching these cars launch, I think the failures are a combination of things. I'll list what I think the worst offenders are, starting with the most damaging to the stock clutch.
(1) The slave cylinder restricter. Obviously, this little guy is designed to make the clutch slip and protect the tranny. You launch the car at RPM, you can guarantee a thorough clutch roasting.
(2) First gear is too long. As short as the gearing is in this car, first sure is tall! It is 40mph capable at stock redline. Both Subarus are well into second gear at this speed. Slip/dumping into a tall first gear is very hard on an AWD car's clutch.
(3) Sticky tires with big 235 section width. Not a lot of room to spin the tires too much there at all. Hence extreme clutch disc burning.
(4) Two foot rubber clutch line from master cylinder. IMO, this one is sketchy at best. The pressure plate has already proven to work well, and when I switched, I felt a slight improvement in feel, but does the OEM piece balloon enough to make the pressure plate not function at 100%? I really doubt it. I've **never** smelled burning clutch in this car (probably because I haven't launched it), and even at WOT full lift and back on upshifts, my stock clutch has performed perfectly. Twice since I've owned this car I've grinded second gear. Once before replacing the clutch line, and once after. I don't think the line effects the response time of the pressure plate. Something like that would have never made it past Mitsu quality control.
Well, my car got the restricter pulled and the SS line at 800 miles. Those are #1 and a distant #4 on my list, and I'm wondering if anyone on here has had a clutch failure with the restricter pulled?
I think #2 and #3 deserve more attention than they are currently receiving, especially #2. These will bear out moreso if failures keep occuring even with aftermarket units. Right now, the only seemingly sure-fire way to make this clutch last is to not launch the car.
Input is welcome.
I agree with you on most points.
Sep 22, 2003, 11:04 AM
#4
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I was out this weekend with my G-tech pro, and have some personal feedback regarding what I think is really causing the biggest problems. I have over 10K miles on my car and this was my first attempt w/ my Gtech which has ridden in my past 12 cars(and truck).
I have noticed that by using even a limited amount of slip to launch the car, the power and traction of AWD easily overcomes the clamping force of the pressure plate. The restrictor may have some affect, but the bottom line is that even after the restrictor, and line expansion are out of the picture, you still have clutch slip that in my opinion is strictly related to a weak pressure plate.
Certainly once the disc gets glazed the problems are exacerbated. I remember reading some tuners feedback that the clutch disc material was pretty decent, but the PP is the weak link for the Evo. This is the part that gets my thumbs down vote!
I had experienced this one other time at a stoplight launch, and had since tried to avoid this from happening by not doing high RPM launches! Guess I don't learn too well!
Btw- I only did one 0-60 run at 5.12 and the brief smell of the clutch made me decide to just go enjoy driving the curves instead
Pity, because with no clutch slip and a little practice I think theres at least a 4.8 in my car (and me).
Just my .02 since it was on my mind recently!
N10S
I have noticed that by using even a limited amount of slip to launch the car, the power and traction of AWD easily overcomes the clamping force of the pressure plate. The restrictor may have some affect, but the bottom line is that even after the restrictor, and line expansion are out of the picture, you still have clutch slip that in my opinion is strictly related to a weak pressure plate.
Certainly once the disc gets glazed the problems are exacerbated. I remember reading some tuners feedback that the clutch disc material was pretty decent, but the PP is the weak link for the Evo. This is the part that gets my thumbs down vote!
I had experienced this one other time at a stoplight launch, and had since tried to avoid this from happening by not doing high RPM launches! Guess I don't learn too well!
Btw- I only did one 0-60 run at 5.12 and the brief smell of the clutch made me decide to just go enjoy driving the curves instead
Pity, because with no clutch slip and a little practice I think theres at least a 4.8 in my car (and me). Just my .02 since it was on my mind recently!
N10S
Sep 22, 2003, 11:30 AM
#5
Originally posted by N10S
I was out this weekend with my G-tech pro, and have some personal feedback regarding what I think is really causing the biggest problems. I have over 10K miles on my car and this was my first attempt w/ my Gtech which has ridden in my past 12 cars(and truck).
I have noticed that by using even a limited amount of slip to launch the car, the power and traction of AWD easily overcomes the clamping force of the pressure plate. The restrictor may have some affect, but the bottom line is that even after the restrictor, and line expansion are out of the picture, you still have clutch slip that in my opinion is strictly related to a weak pressure plate.
Certainly once the disc gets glazed the problems are exacerbated. I remember reading some tuners feedback that the clutch disc material was pretty decent, but the PP is the weak link for the Evo. This is the part that gets my thumbs down vote!
I had experienced this one other time at a stoplight launch, and had since tried to avoid this from happening by not doing high RPM launches! Guess I don't learn too well!
Btw- I only did one 0-60 run at 5.12 and the brief smell of the clutch made me decide to just go enjoy driving the curves instead Pity, because with no clutch slip and a little practice I think theres at least a 4.8 in my car (and me).
Just my .02 since it was on my mind recently!
N10S
I was out this weekend with my G-tech pro, and have some personal feedback regarding what I think is really causing the biggest problems. I have over 10K miles on my car and this was my first attempt w/ my Gtech which has ridden in my past 12 cars(and truck).
I have noticed that by using even a limited amount of slip to launch the car, the power and traction of AWD easily overcomes the clamping force of the pressure plate. The restrictor may have some affect, but the bottom line is that even after the restrictor, and line expansion are out of the picture, you still have clutch slip that in my opinion is strictly related to a weak pressure plate.
Certainly once the disc gets glazed the problems are exacerbated. I remember reading some tuners feedback that the clutch disc material was pretty decent, but the PP is the weak link for the Evo. This is the part that gets my thumbs down vote!
I had experienced this one other time at a stoplight launch, and had since tried to avoid this from happening by not doing high RPM launches! Guess I don't learn too well!
Btw- I only did one 0-60 run at 5.12 and the brief smell of the clutch made me decide to just go enjoy driving the curves instead
Pity, because with no clutch slip and a little practice I think theres at least a 4.8 in my car (and me). Just my .02 since it was on my mind recently!
N10S
Sep 22, 2003, 11:43 AM
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i managed to pull off a 4.4 second 0-60 in my evo on stock boost, rmr exhaust and custom grounding kit. I also had a friend in the car along with spare tire, a bunch of crap in the back seat and my stereo system. Now with 20psi to redline boost controller and without all that stuff in my car, i think i could pull an easy 4.2 second 0-60. Oh about my clutch, ive launched this car couple times. Once i accidentally launched at 7000 rpm which was really really bad. Sometimes if i dont press the clutch down enough going into 5th gear it grinds a bit, but other than that, no issues. I have almost 6000 miles.
PS i got my time using a HKS Type-1 turbo timer which has a VERY VERY accurate reading. Much more accurate than any g-tech.
PS i got my time using a HKS Type-1 turbo timer which has a VERY VERY accurate reading. Much more accurate than any g-tech.
Sep 22, 2003, 11:48 AM
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my question would be, for those who have done so, is it safe to launch the car WITH a very good aftermarket clutch? Can the tranny take it?
Percy
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Sep 22, 2003, 12:00 PM
#8
Actually ACT said the whole clutch setup was pretty good...but if they had to pick a weak link it would be the pressure plate. They said the clamping lb rated higher than the Sti. I think part of the problem is improper break-in on the clutch. This could have happened before the owner even took delivery from the dealer. If the dealer did high rpm launches or put alot of stress on the new clutch in any way it would kill its lifespan. Centerforce recommends being real easy on a new clutch for about 300 miles...basically keeping the rpm's relatively low and babying it.
We have more clutch/tranny issues in the US than anywhere in the world..and yes, it's because of the way we drive compared to other parts of the world.
I think the stock clutch is fine for a factory clutch. It seems to clamp good and perform pretty well overall. I launch my Evo autox'ing at 5000+ rpm's (without popping the clutch) and can spin/smoke all 4 tires launching (nearly stock) and then run it for 60 seconds at a time on the course, using the clutch more than I would drag racing, and don't have a problem with burning clutch smell or slipping (knock on wood
). So far I have 5700 miles.
So, I think break-in for the first 300 miles or so may be the most important factor.
We have more clutch/tranny issues in the US than anywhere in the world..and yes, it's because of the way we drive compared to other parts of the world.
I think the stock clutch is fine for a factory clutch. It seems to clamp good and perform pretty well overall. I launch my Evo autox'ing at 5000+ rpm's (without popping the clutch) and can spin/smoke all 4 tires launching (nearly stock) and then run it for 60 seconds at a time on the course, using the clutch more than I would drag racing, and don't have a problem with burning clutch smell or slipping (knock on wood
). So far I have 5700 miles. So, I think break-in for the first 300 miles or so may be the most important factor.
Sep 22, 2003, 12:24 PM
#9
Man, I agree with the breakin thing completely. I babied the crap out of this car for the first 600 miles, then only got on it a bit between 600-1000. But it had 37 miles when I bought it. For all I know, it could have 200 hard launches from the dealership itself, but I'd like to believe that isn't the case. The alst three cars I bought before this one, I peeled the delivery tape off and they had 7 miles or less. I could've got a Blue By You car, but they would've had to dealer transfer it, and some guy was going to physically drive it 50 miles to me. I was like "Um, NO." If I could pick it up, maybe a different story. Hopefully this clutch will be good to me for awhile. \\
I'd still really like to get to the bottom of all this, though. Keep these technical ideas flowing, please!
I'd still really like to get to the bottom of all this, though. Keep these technical ideas flowing, please!
Sep 22, 2003, 01:20 PM
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Originally posted by Noize
So you have the restricter and line done as well? My case for the pressure plate was Dirk at ACT saying it had almost full clamp force when he physically tested the one that came with that totally dead disc. I'm a little hesitant to believe a 2100/2200 lb pressure plate isn't strong enough for a low 13 second car. If you're burning like that with the SS line and restricter removed, then I might never drag race this car.
So you have the restricter and line done as well? My case for the pressure plate was Dirk at ACT saying it had almost full clamp force when he physically tested the one that came with that totally dead disc. I'm a little hesitant to believe a 2100/2200 lb pressure plate isn't strong enough for a low 13 second car. If you're burning like that with the SS line and restricter removed, then I might never drag race this car.
The two times I have encountered clutch slip, I wasn't slipping it hard to launch, just a little bit. Once started though the PP just doesn't want to grab. If you think about that, and the fact that a number of folks have said the clutch plate material is good quality, I just don't know what else it could be. The issue may be less oriented towards the 1/4 mile capability of the car, and more towards the power characteristics of the engine as the turbo spools-up during slip, and the AWD on the other end of the business which is locked in tight traction with the asphalt. The combo may just need more clamping force to maintain grip.
Again sorry for making any confusing statements regarding the line and restrictor.
N10S
Sep 22, 2003, 01:22 PM
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Originally posted by XRS-Lift
i managed to pull off a 4.4 second 0-60 in my evo on stock boost, rmr exhaust and custom grounding kit. I also had a friend in the car along with spare tire, a bunch of crap in the back seat and my stereo system. Now with 20psi to redline boost controller and without all that stuff in my car, i think i could pull an easy 4.2 second 0-60. Oh about my clutch, ive launched this car couple times. Once i accidentally launched at 7000 rpm which was really really bad. Sometimes if i dont press the clutch down enough going into 5th gear it grinds a bit, but other than that, no issues. I have almost 6000 miles.
PS i got my time using a HKS Type-1 turbo timer which has a VERY VERY accurate reading. Much more accurate than any g-tech.
i managed to pull off a 4.4 second 0-60 in my evo on stock boost, rmr exhaust and custom grounding kit. I also had a friend in the car along with spare tire, a bunch of crap in the back seat and my stereo system. Now with 20psi to redline boost controller and without all that stuff in my car, i think i could pull an easy 4.2 second 0-60. Oh about my clutch, ive launched this car couple times. Once i accidentally launched at 7000 rpm which was really really bad. Sometimes if i dont press the clutch down enough going into 5th gear it grinds a bit, but other than that, no issues. I have almost 6000 miles.
PS i got my time using a HKS Type-1 turbo timer which has a VERY VERY accurate reading. Much more accurate than any g-tech.
Sep 22, 2003, 02:06 PM
#13
Originally posted by N10S
Noize....sorry for not being more specific. I have driven a car with the SS line, but mine is still stock. My comments are just based on my experiences with many past performance cars, launching techniques, and clutch charcteristics. My biggest concern is that I am pretty decent at launching AWD turbo cars having had a talonTSI awd, 2 modded S4's, a stage 3 WRX, and now the Evo.
The two times I have encountered clutch slip, I wasn't slipping it hard to launch, just a little bit. Once started though the PP just doesn't want to grab. If you think about that, and the fact that a number of folks have said the clutch plate material is good quality, I just don't know what else it could be. The issue may be less oriented towards the 1/4 mile capability of the car, and more towards the power characteristics of the engine as the turbo spools-up during slip, and the AWD on the other end of the business which is locked in tight traction with the asphalt. The combo may just need more clamping force to maintain grip.
Again sorry for making any confusing statements regarding the line and restrictor.
N10S
Noize....sorry for not being more specific. I have driven a car with the SS line, but mine is still stock. My comments are just based on my experiences with many past performance cars, launching techniques, and clutch charcteristics. My biggest concern is that I am pretty decent at launching AWD turbo cars having had a talonTSI awd, 2 modded S4's, a stage 3 WRX, and now the Evo.
The two times I have encountered clutch slip, I wasn't slipping it hard to launch, just a little bit. Once started though the PP just doesn't want to grab. If you think about that, and the fact that a number of folks have said the clutch plate material is good quality, I just don't know what else it could be. The issue may be less oriented towards the 1/4 mile capability of the car, and more towards the power characteristics of the engine as the turbo spools-up during slip, and the AWD on the other end of the business which is locked in tight traction with the asphalt. The combo may just need more clamping force to maintain grip.
Again sorry for making any confusing statements regarding the line and restrictor.
N10S
I still want to hear some feedback from people with the restricter removed and the SS line installed. Have you raced your car? Is the clutch holding up? I want to find the core of the problem so we can all have more fun with this car!
Sep 22, 2003, 09:14 PM
#14
I have the SS line in and restrictor removed. Also, I have a Clutch Masters Stage 3 in the car now. I would guess that the pressure plate is about 2700-2900 pounds of clamping force. It is rated at 500 hp and comes with a carbon-kevlar disk that requires 500 miles of break-in. This clutch grabs really firm and if you drop it out to fast on a gear shift you will slip the tires which I wouldn't recommend since you might damage the drivetrain with that sort of shock. Smooth quick shifts is the way to go. As far as launching, I won't be doing any of that for a while. Just normal driving involves alot more attention as the clutch grabs really fast. Not thinking about it you will nearly stall the car out. I really like my new clutch, but I would recommend the stage 2 for easier driviblility IMO.
Sep 25, 2003, 10:14 PM
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I own a 94 3000GT front wheel drive. I have had a lot of fun times dropping it from redline and roasting the tires. Never in the 235,000 miles of it's life have I ever smelled the clutch. Nor have I replaced one due to failure. I replaced the original clutch when I installed the the new transmission at 207,000. Which from what I hear is outstanding mileage for this car to hold up. I've seen 2 at the dealer since getting new trannies both well under 100,000 miles. The point of this whole story is that my driving style has only gotten better if changed at all since I was an 18 year old punk in a fancy sports car. Why the sudden change in reliability?