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Why break-in a clutch?


slow4now

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I have heard time and time again that people insist on breaking in their clutches for x amount of miles. Why is that? I can't think of any reason you would need to, but if their is a good reason I would like to know it. I mean it's just a spring with two surfaces that rub together, it isn't like there are any rings that need to seat like when breaking in an engine. Anyone have any insight besides "because that's what your'e supposed to do"....???? No smarty-pants replies, I honestly would like to know. Thanks!
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Well, First off, you should ALWAYS resurface the flywheel when you do a new clutch. The clutch gets hot and needs a fresh surface to grip on to. There is a glazing effect that is required to have a clutch adhere to the flywheel properly, otherwise you will have a slipping clutch in no time.
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Guest neonfink

Ive heard if you take your time and break it in for X ammount of miles before you run it harder that it will last longer, but if you just jump right on it, it will still work fine, just wont last as long.

 

I dont remember where I heard that though.

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I know people who have done both ways breaking them in and not breaking them in. Neither to my knowledge has had more/less problems with either way. I break mine in for like 250 miles varying RPM range and speed.

 

I know that cars sometimes change them at the track and then go beat on em in like a half hour after putting it in. So I don't think either way is better IMHO. Maybe ask a clutch company?

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Well from searching on the net all I am coming up with is that it helps the clutch disc properly seat with the flywheel. So I guess it takes down the high spots more gradually. I still don't see why it would matter whether you took the high spots down in 50 miles of driving or 500.......hmmm
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The mating surfaces, flywheel to clutch disk, and clutch disk to pressure plate, are not all perfectly flat surfaces when they are new. So the actual surface area of the mating surfaces is smaller on a clutch that has not been broken in. So you are requiring the clutch to provide max force, aka static friction, with a reduced surface area to produce that static friction. Less surface area in contact means less friction. So you have a greater risk of ripping the clutch disk free even when the pressure plate is fully engaged. This basically smokes a brand new clutch, because all that kinetic friction once the clutch is spinning is just dissipated as tons of heat, causing all the surfaces to glaze over as Nick stated. Once you have that glazing, chances are the clutch will never have that level of friction again. The flywheel can be resurfaced to get rid of the glazed upper layer, but the clutch disk is porous just like brake pads, so it is difficult to get out imbedded impurities, which what glazing the disk really does since the extreme heat causes it to change states. I don’t see too many people resurfacing clutch disks either. After whatever break in period, the disk has seated as you mentioned, so your surface area is larger, and your chances of smoking the clutch and glazing it over are smaller.

 

I have also seen cars abused at the track only minutes after installing the new clutch setup, and most have been fine. But it has been proven that the clutch will last longer if you are nice to it at first. Talk to the manufacturer to see what they recommend. That way if you smoke your clutch within the first 50 miles, they cannot blame you for improper break-in. I know that I don’t want to replace a nice new $400 clutch twice because I got impatient, I just don’t have that much extra $$ to spare.

 

BTW, new brake pads on the track cars around the shop need to be “seated” as well to work their best, for the same reasons as a clutch, the mating surfaces aren’t perfectly aligned yet.

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Originally posted by neonfink:

Ive heard if you take your time and break it in for X ammount of miles before you run it harder that it will last longer, but if you just jump right on it, it will still work fine, just wont last as long.

 

I dont remember where I heard that though.

I'll second that. I got the info from Dirk at ACT.

 

Jamie

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basically you dont want to SHIFT hard, once youre in gear, it matters not what you do.

 

I have broken them in, and I have beat the crap out of them 10 minutes after installing them...no difference...

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Originally posted by rl:

basically you dont want to SHIFT hard, once youre in gear, it matters not what you do.

 

I have broken them in, and I have beat the crap out of them 10 minutes after installing them...no difference...

Sorry, that is not correct. Even if you granny shift it, you can still ruin a clutch with a full power roll on, I have seen it happen, see above post for the reason. Obviously, the less power the car is making, the less problems you will have though.
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Thanks for the replys guys. I also thought of it in the same terms as breaks, it's just two surfaces rubbing together. So you have to properly heat cycle them just like new brakes. I must've scrubbed off at least a few hundred miles of clutch life this weekend :D:eek:
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The recommendation from ACT/Racing Beat on my Clutch/Flywheel were "moderate driving for the first 300 miles".

 

My interpretation of moderate driving is no WOT, no side stepping, and no excessive slipping. :D

 

K

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