A close to accurate understanding of how a clutch works is quite an insult. I am a heavy equipment, heavy wheeled vehicle, and tracked vehicle specialist by military training with over 22 years of practical experience. Almost all of these vehicles use a standard single plate clutch system with varying numbers of gears. You have no idea of my experience or expertise and I have no idea of yours. A race car with a standard clutch is far different than a pig of a car with an improperly sized and matched clutch setup. This whole discussion was based off the fact that I simply stated that I was surprised that AM chose a manufacturer that I have dealt with in the past that have known problems. A race car is a light weight vehicle and yes, when rev matching and getting the car underway, there is very little wear on the clutch components. Not only that, a "ONE OFF RINGER" does not support a theory, just because your clutch has lasted for the 130 hours or 120 hours, whichever you choose to stand by, does not mean it is the norm. However, you are making an apples to oranges comparison. A car that weighs close to 3600 lbs needs more than 1-2 hp to get moving, and in traffic there is constant slipping of the clutch no matter how careful you may be. I have owned countless cars with clutches that have lasted far more than 50K miles, hence my original statement about the poor quality of the AM clutch choice. Let us know when the clutch goes out in your Aston. It will be an interesting discussion on correct technique and lack of driving ability to all listening. These clutches, from the cases I have seen both on here and Pistonheads, show a pattern of failure prematurely. Since we don't live in the theoretical world you describe, clearly there is a problem with the clutch quality from the start. Yes, there may be times we have all slipped a clutch in traffic or other instance, but suggesting that everyone that has a clutch fail or start to fail at 50K miles is incompetent to drive a manual transmission, sure isn't going to win you any friends. My real world experience has taught me many things about theory and actuality.. As has combat experience. There is the way the engineers design things to work, then there is the way they actually work. Combat experience is the same, there is the way the "theorists and experts" suggest a battle is fought or contact is made, then that all goes to **** when the first shot rings out or first IED explodes and half of your squad is blown into small bits and there are now 3 of you left to do the same mission. Theory is great on paper... And that is all it is good for! Good day sir!

 

some great posts in this thread!
Chris

 

I think I have an understanding of where you are coming from, and you might know my vantage point. There is no question that the clutch is weaker than some out there on other performance cars. I have brought you to the table some theory, based on some actual imperical evidence and facts. The assumptions are minimal..... to coorelate your military heavy equipment operation to this discussion, is a stretch, though from my side, it comes with a huge amount of respect. But, working heavy equipment, and driving a fickle race car/street car might not have too much in common. Also, by your statements of why you avoided the dyno, until you had the clutch "broken in" tells me that you might not know how the clutch works. On a dyno there is NO slipping of the clutch. its in gear. the clutch disc is pressed in place to the flywheel and doesn't move, and therefor , doesn't wear. if it does, you have BIG problems. That you were happy that you had no slippage in 5th gear climbing a hill. that's not a clutch performance validation, that just shows the clutch is not broken. in fact, if you had slippage prior, that's a pressure plate problem, unless the disc came apart on the prior clutch.


The criticism was of your description of clutch operation and wear risk was incorrect in the most important areas.
1. You made it sound like you have to tippy toe the car around town .
2. That you wouldn't even dyno the car until it had some miles on it
3. That there was wear, no matter how well you matched engine RPM to car speed.
4. That it takes more than a couple of HP to get the car rolling if its "heavy" like the AMV8


Those first 3 things alone were things I was trying to help make clear and correct for those that might be prematurely wearing out their clutch. Basically to fight the misnomer that these clutches are so weak, that they should wear out between 20 and 50k miles.
The main point here is that on a shift, If the clutch is strong, there is no slip, thus no wear. drive it to redline all day long and make hard shifts. drive that mountain road like you are Ken Block. there should be negligible wear. I'm not talking speed shifting here , using mismatched RPM releases, I'm talking best effort shifts, but even poorly executed ones are fine.
There are two ways you can release a clutch from a stop light or jack rabbit racing start. the high wear way, or the low wear way. our clutches don't like high RPM releases. they have a soft surface construction and high force pressure plate., so you need to :
1. dump the clutch quickly if you have any substantial rpm, almost chirping the tires or burn out.
2.keep rpm low (1200rpm) and release clutch slow until you have movement and then apply throttle and have full release at the same time soon after movement of the vehicle.
3. keep the cutch pedal out. have the car in neutral when ever its stopped or just before stopping. never ever have the clutch pedal depressed at a stop light or in traffic stopped. the clutch is for only selecting a gear.


Yes, I am suggesting that some here might not drive the clutches correctly. in fact, most drivers in the world don't, but the manufacturers make them to survive abuse anyway. I've been instructing on the race track for 10 years (mostly racing), and most don't know how to do a lot of things very well in a car until they are coached to change. A mid pack club racer can take a stock Miata, can embarrass 90% of all Viper drivers at the track.
Knowledge is king. You get knowledge from people that know, not by instinct or hours and hours of driving without the knowledge. Its why a career cab driver usually cant drive a race car very well even though he has a billion miles of experience.


I provided some theory, based on the basic workings and physics of clutches, and I provided some empirical evidence to support it as well. you have to admit. a race car/ with license plates, with 50k street miles that still has the printing on the disc surface, is quite a testimonial. Also, this is no special disc. its a stock street clutch, and it was on a performance car that was also heavy, and used for over 120hours of racing! (some even on TV ) If you truly understand how the clutch work and the forces applied to it, then all of what I'm saying will make sense.


sure, I agree with you . (especially after hearing the brand of clutch found to be used in our AMV8) the clutch is weak. its more a wear item on our cars than any others I know of in this performance range. BUT, that's why I'm posting this. even through its weakness, it can last as long as the car , if some precautions, and style changes are made to how its driven. Again, never compromising on performance , just style changes. Now, if you live in San Francisco, or drive LA stop and go traffic every day on the 405, sure expect some wear issues, more so on the AMV8 than others. BUT, if not for those two situations, you should get many miles of good service from the clutch (if you don't have one of those rivet popping defective ones )


The bottom line is that a high slip release (high rpm release) of our clutch, will kill it in short order. Driving the AMV8 without too much slip in the clutch, should allow the clutch to last the life of the car even being driven extremely hard!

 

XWCGT and ArtB, with all the respect that's due, how about the two of you agree to disagree?

 

He just had too many assumptions that I had to dispel due to his premature wearing clutch. Its not good for the group to just walk away without providing explanations for how the clutch can wear prematurely, and how to prevent it, without sacrificing performance. I'm not trying to win any competition here, its just a discussion.

 

There is no assumption that I have that you need to dispel. On the contrary, I am beginning to think that you have the notion that once the clutch is engaged, it has no physical way of slipping. This is simply not true. I was not going to dyno the car with the slipping clutch because under load, on the dyno, the clutch would slip, just as on the road. The roller on the dyno is a set weight. The dyno figures out HP by knowing how quickly the car can accelerate said roller over a given time period. If the clutch disc is worn, and load is applied it would still slip on the dyno. I am not sure how to make it clear to you. Knowing how to drive a race car and how to make the revs match etc, does not make you knowledgeable of the mechanics of a manual clutch. I have met several race drivers that know little to nothing about what makes their race car go, but can drive the wheels off of their car. I was an instructor for PCA for about 9 years, before selling my track car when my son was born, although I am no racer, I have thousands of hours on track and in a track only car.

The input shaft from the transmission is attached to the clutch disc. The pressure plate is attached to the engine. If the clamping force of the pressure plate is reduced by a failing set of springs on the pressure plate, or by a worn clutch disc, or worn pressure plate, the engine speed will not match the drive wheel speed or just fail to hold the load and therefore begin to slip. Even though the clutch is fully engaged, when the disc is no longer able to hold the friction required to stay at the same speed as the engine, the engine out accelerates the car/wheels. To say that if the clutch slips on the dyno you have big problems. Yes, the clutch was worn and was slipping on the street under acceleration. I bought the car with 48K miles on it. So the clutch was close to the end when I got it, even though it didn't slip when I first got it. I fully understand the mechanics, and have seen many clutches slipping in higher gears under load and need replacing, as well as I have seen several high hp cars have clutches slip on the dyno under load, especially on a Mustang dyno that puts an electromagnetically controlled motor load against the rollers to measure HP, and usually why they register lower hp numbers than a Dynojet.
Here is a good animation of clutch operation. The portion that is important is the disengagement and engagement of the disc assembly. Even though there is minimal variance in engine speed to the disc speed, when disengaged and then reengaged, there is still a small amount of slippage when the disc contacts the pressure plate and flywheel. This wears the friction disc over time and eventually why it slips.

http://www.youtube.com/watch?v=5_rCXhAi6Jg

 

yes clutches should be broken in . jUST as new brake pads should be broken in/ bedded in . Reduces the chance of hot/hard spots (overheated blue spots on flywheel and pressure plate) and better mates the clutch surface to the flywheel pp

 

You are right in saying, if there is slipping, there is major things wrong. a clutch shouldn't slip, if it is worn. its a bad or weak pressure or the discs are so worn, that the pressure plate pressure is less, due to the deflection being reduced. usually worn discs don't create slip, but they can depending on the pressure plate design.


I was referring to your comment that you didn't want to go to the dyno until the clutch was broken in...... not needed . if its working, it wont slip. no breaking in, will change the force that the clutch can provide to keep synchronous coupling.
By the way, I not only race, ive built many race cars and race engines, and have many years of experience in the arena of power transmission systems.
ahh, now opening pandoras box of why one dyno registers higher than another. brake dynos vs interial dynos measure the same. if they are different, they are defective or have been tampered with. inertial dynos measure your power at full throttle. its a Power measuring device, because its measuring rate of change of kinetic energy. (by definition, is power) . its very simple. the brake dyno (mustang dyno ) is a eddy current dyno, but has been calibrated to know how much current, or power is required to allow the powertrain to accelerate a known load.. regardless, if the clutch is not slipping, its registering its full power output, just as it would on the street. a cars engine doesn't know if you are in 5th gear or 1st gear. the engine puts out the full torque at full throttle, its the same in any gear. what you might have noticed is that your 5th gear run was at a max torque level of the engine, vs your lower gear runs , running through max torque so quickly, that the lower torque at the higher rpm, doesn't break the clutch free.


Ill look at the animation, but you have to realize, the minimal slip doesn't result in any measurable wear. its the high rpm release slip that does. think about it. 1200rpm, that's 20revolutions in a second. How long does it take to release the clutch at this speed 1/8 of a second. you get a progressive friction over 2 revolutions of the flywheel. trust me, there is no wear happening here. But, if you rev the car to 3000rpm and release over several seconds.......... there is the wear and heat issue. that's my only point.
again, clutches are not good or designed for dissipating heat. there is very little wear on quick release of the clutch. it takes very little clutch force (friction) to start a car rolling. near matched RPM shifts, create little wear at all. if a clutch is worn at 50k miles, its due to someone slipping the clutch way way too much in 1st gear and reverse.

 

No, this is not true at all. brakes need to have the resins baked out to handle heat , friction ,etc. Clutches are broken in from the moment you do your first few releases. ever had a new squeaking clutch?
Art was going to avoid the dyno until it was broken it. it has no bearing on the full throttle operation, because at full throttle, and clutch released, the flywheel and clutch are basically nailed together. There is no slip, and if there is, there is a problem.
With a clutch, there is no need to wait for anything you would want to do with the car.

 

How about XW you take this discussion private to private message and not hijack a vendors thread...

That would be the proper forum etiquette

 

I can always start a new thread if needed.

 

Is the new disc material more durable than the stock version? if its more durable, it might have less grip , that might be a good think in my opinion, and be more forgiving for the higher RPM slip starts. Im a little worried about the clutches that have slipped when the lining has gone thin. THIS should not happen. the pressure plate should be able to keep adequate pressure on the flywheel with verylittle to no lining at all. after all its only about 2mm thick, front and rear. with 4mm missing, the pressure plate should be designed to not slip even with slightly less pressure due to the slightly further distance to make clutch disc to flywheel contact.


is the new version of the pressure plate, higher force than stock?

 

FULL throttle on a dyno means full load on everything that includes the clutch....a broken in clutch with be (nailed together as you say) even better ...ask afew mechanical engineers

 

Please do. Let's keep this thread specific to the Vender/OP's product.

 

Your talking to one. full throttle means full load on the drivetrain as torque, but for those parts that are not moving apart or together, there is force, torque, no movement. AND no movement , means no, force or torque, and no power dissipated, which means no wear or heat. (a good analogy is someone sitting on a chair. There is the force of gravity, but the chair is pushing back with equal force , so there is no net force. ) So, no movement, so no power, no heat, or anything. its steady state . If the clutch is slipping, then its broken. this usually this means the pressure plate is not strong enough. Even if the clutch surface is worn down to the rivets, it should (if its working correctly) hold. however, once I starts to break free from the "sticktion" of the disc being pressed to the flywheel via the pressure plate, then you will have friction, heat, wear, that all will accelerate as the flywheel progressively spins faster than the clutch and driveline.


So, on the dyno, as long as the disc doesn't move relative to the flywheel, you can dyno all day long and nothing will happen to it. its basically locked together. there is no need for break in. The slight amount of "break in" that occurs is the parts do get more friendly and can change the release characteristics slightly, but clamping pressure is not changed. if you were to "fry" a clutch, its better to do it with one that has a little wear on it, or glazing might be more likely. But on a dyno, the clutch isn't really a factor for how its used.


all the reason to go to the upgraded pressure plate that stuart is offering when its time for a clutch change. plus it sounds like the clutch discs have a better surface on them, maybe a bit harder than stock. Stuart can answer this better. (to keep things back on track here . )


Ill start another clutch thread so that we can discuss the clutch issues. maybe even someone that has done the job himself, can post pics.
clamping force numbers of stock would be nice to know. also, the equivalent Valero part for the discs so we can see why they wear so fast, under abusive operation.