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Unread 06-28-2009, 10:40 PM   #1
JeffB
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Question about destroying clutch plate WITH CLUTCH PEDAL DEPRESSED

I read an article online that a guy described blowing up his clutch in an unusual way. He claimed that his clutch blew up while he had pedal fully depressed. He was coasting down a hill in first gear with the clutch fully depressed at about 30 miles per hour when his clutch basically blew up. He said his clutch was rated for up to 6000 rpm but due to his speed and having the shifter in first gear (despite having the clutch fully depressed) that his clutch exceeded 6000 rpm and failed catastrophic, despite having the clutch completely disengaged

I don't understand the finer points about the clutch but I always thought as long as you kept the clutch fully depressed that you were OK, no matter what gear you were in or what speed of travel.

Is this true and under what particular circumstances can this happen?

BTW, the guy was driving a re-geared CJ but said it could happen to a stock Jeep.

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Unread 06-29-2009, 04:48 AM   #2
wushaw
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Interesting...what exactly blew? Pressure plate, clutch disk, flywheel, throw out bearing, pilot bearing? The clutch disk is about the only thing that could have come apart since it is splined to the tranny input shaft and him in first going 30mph it would be spinning between the flywheel and pressure plate at a pretty good click and the material riveted to the disk could have let go.
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Unread 06-29-2009, 07:59 AM   #3
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The friction material WILL come off at a high enough RPM. I've seen it happen with a missed downshift happen with a missed downshift.
We did a Cavalier who's driver was known for not having any grass grow under his tires. Tech brought me the clutch plate...not a trace of friction material on it, but all the rivets were still in the holes, jingling like a tambourine...lol

Somebody that knows diff/transfercase/trans ratios should do the math and see just how easy it would be to overspin a clutch disk by coasting in gear like that.

Not sure WHY someone would be coasting at 30mph with the trans in 1st....good rule of thumb....don't do it.
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Unread 06-29-2009, 09:13 AM   #4
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Originally Posted by gcfishguy View Post
Not sure WHY someone would be coasting at 30mph with the trans in 1st....good rule of thumb....don't do it.
No doubt!!
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Unread 06-29-2009, 11:45 AM   #5
Ole Yeller
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I guess it's possible. I had a clutch on an old Oldsmobile 442 come through the bellhousing and dent the floor right next to the accelerator. Not fun.
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Unread 06-29-2009, 11:56 AM   #6
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Edit: Nevermind.
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Unread 06-29-2009, 12:09 PM   #7
Ole Yeller
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Jerry - I respect your knowledge without question most in not all of the time, but I think you are wrong on this one. The pressure plate is bolted to the flywheel and therefore turns with the flywheel and engine. The clutch is "floating" between the flywheel and the pressure plate and riding on the transmission input shaft. I think the clutch disk will turn at the same speed as the transmission input shaft.

IE, when you are sitting still, in gear with the clutch depressed, the clutch is not turning even though the motor is idling at 800 rpm. I'm not even going to try to do the math on what the input shaft would be turning at 30 mph in 1st gear, but no doubt it was yelling for help. Not a smart move.

I think mine would hit about 5,000 rpms at around 15 mph tops.
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Unread 06-29-2009, 12:18 PM   #8
Jerry Bransford
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Whoops you are right Ole Yeller, I was thinking about it with the clutch disengaged and you'd think I'd remember which shaft it sits on around after the several clutch jobs I have done.
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Unread 06-29-2009, 12:20 PM   #9
Ole Yeller
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It's always good to be able to correct the expert every now and again.
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Unread 07-20-2009, 09:45 AM   #10
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Yeah that's wild,likewise I dont understand how that could happen if the clutch was disengaged.On the otherhand if he was coasting down hill at that rate in 1st gear while engaged.........hmmmmmm guess he got what he was asking for
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Unread 07-20-2009, 09:50 AM   #11
Ben_321
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ive heard of this happening before especially in low range and in 1st gear....so i suppose if for whatever reason you want to roll fast down a hill then you should shift to neutral
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Unread 07-20-2009, 10:21 AM   #12
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Is this one of the "It's on the internet so it must be true" threads.


If the guy was in 4 low, coasting down a hill, moving fast, and let out the clutch...he should be glad that's all that failed.


I shreadded all the material off mine but I am still unaware what caused it. Falutly from the mfg. more then likley.
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Unread 07-20-2009, 10:29 AM   #13
NotURMailman
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It can happen! I had a clutch disc in my 2WD S10 explode on me when I went back into gear (1st) out of neutral too soon while coasting to the end of an interstate off ramp when I was in college. DOH! The friction material literally grenaded. I was one of those "in theory it could happen, but yeah right" know it all punk kids. It was only a two month old clutch, all be it not the best quality (AutoZone). One of those lessons I had to teach myslef the hard way...
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