Who's done it? Fess up. You come to a long hill and don't want to shift out of low range so you just put the clutch in and coast, speed picks up, then a loud bang is emitted from under the truck. The clutch over revved and exceeded its rpm rating, causing it to simply explode.

I did the starter a couple weeks ago and found that there was a chunk of the bell housing missing the size of a penny. The bellhousing also had weird chips in it that seem almost like the chip peeled without any scratching to the bellhousing. I couldn't figure how those came from a any outside blow, but I never thought about an impact from the inside...

 

What? That can happen? Ive coasted like that but never had any damage.

 

The only way a clutch could over-rev is if the ENGINE was over-revving as well; they're ATTACHED....???

Now, if you were in 2nd gear on a 15% grade and hit 90 mph, I could understand....

 

sounds pretty wierd, clutch pressed thats seperates it from motor??

 

most of the time il put it into neutral

 

I usually just put mine in neutral as well. But I never coast with the clutch disengaged and the truck in gear. Glad I read this so I never do that. . .

 

Only real time i do coast with it engaged is when im out 4x4in and come across a step part.

 

Lessons learned....

 

Part of the clutch is attached, part is not (when disengaged). That's the whole purpose of a clutch, to seperate (at will) the engine from the driveline.

So apparently its the part that isn't attached to the engine that over-revs and explodes.

 

Again, how FAST would you have to be going to grenade a clutch?!?

 

It depends on what gear you're in. If you've got a ultra-low dual transfer case apparently not very fast at all.

 

i've seen some nasty clutches about to fully fail but never failed. Theres some pics of a guys skyline where the flywheel exploded and cut thru anything in its path tho.

edit.

http://pic.phyrefile.com/2007/07/02/780039wy7.jpg

http://pic.phyrefile.com/2007/07/02/780050oh0.jpg

 

The only time you would need to worry about this is in 4low. Think how fast you can go in 1st gear low. Now if you come to a down hill in 4low and 1st gear and just push in the clutch how fast do you think that disengaged clutch disk is spinning at 20MPH? I'm not going to do the math but its fast, probably 8-9000rpm at least. Most clutch disks are only rated to a free spin of 8000rpm, I would think on a 4x4 even lower as most would never go that high.

The Skyline damage was most likely caused my the Flywheel blowing apart. Its fairly common with hi revving hi powered cars. Not really the same as what Matt was talking about. On a 4x4 in Low its much easier to blow up a clutch disk.

Jeremy

 

I recall an article I saw awhile back that explained it just like that. And thats what happend to the truck they where showing....

 

holy crap!

is that a frame rail it ate through?

 

that is what it looks like! hahaha that happened on a couple early powerstroke's because they used a two piece flywheel and they would come apart during high load/performance situations. they replaced them with one piece flywheels and it solved the problems. our clutches are all one piece and seem relatively stout for a smaller engine. When i put in my MC clutch, i made sure to use grade 8 bolts and loctite on the pressure plate. don't want that thing to come off hahaa

 

That Skyline is unibody, so there are no frame rails like on our trucks, just slightly thicker reinforce portions of the body which add rigidity.

 

No, the Pressure plate is bolted to the flywheel, and spins at the speed of the motor. The clutch disk is on the transmission input shaft, and spins whatever speed it's spinning at. A W56 1st gear is 3.9:1. Say you're running 33" tires, and a 5.29 rear-end. You're in gear, and the motor is at 5000rpm. You're doing 22.6MPH.

Now lets say you're in 4lo with a set of 4.7 gears in your transfer case. You're still in 1st, and decide to coast down a hill with the clutch pushed in. you reach a speed of 22.6MPH. Normally, in high your clutch disk would be spinning at 5000rpm, but because it's in low-range, it's now spinning at 23,500rpm! You don't notice this of course, because you have no way of telling how fast the clutch disk is spinning when it's dis-engaged from the motor. Boom.



Those pictures of the Skyline were in Edmonton about a year ago. I believe it was due to a cracked flywheel.

 

Holy crap, well put grob.

i knew i noticed that pic from somewhere