turbotuner20v

I've already fixed the problem, but I want to figure out if this is a random chance occurence, or if I need to look at how something is setup on the car.

Background:
I have a 2009 Corvette w/ a mcleod RXT clutch, stock slave cylinder and stock master cylinder w/ the clutch assist spring behind the clutch pedal arm removed. The car makes ~900whp. The mcleod has only been installed since the latest build to hit that 900hp (~1k miles).

How I noticed the issue:
The other day I was out in the car and decided to get on it in 1st and 2nd. Both gears are pretty worthless with this much power, so it tapped off the limiter once or twice in 2nd scrambling for traction and then I let out. After that the clutch pedal felt extremely light w/ a low pick up point like it was barely working, but it didn't stick to the floor (clutch spring removed). I was able to drive it a short distance home, but with the light pedal feel and some vibration in the pedal.

I bled the clutch that night and during the bleeding process it felt perfect. I started it up and pushed the clutch in to engage a gear and move it out of the garage and the pedal felt like it did the day before, super light and barely working. I back the car out and move it back and forth in the driveway a few times and the clutch stays soft and there's almost a little vibration coming through it.

I found this under the car and think it came from the inpection port of the bell housing. It's like some kind of plastic ring w/ a raised lip.



I also found this hanging out of the inpection port, similar material.



It looks like there was some aluminum shavings in the bell housing:





I had someone crank it over and then turn it on and it blew some of the same aluminum shaving stuff out of the bell housing ports, as well as this peice of plastic:



I tore the car apart and found this:

The throw out bearing was completely toast.




Some metal dust around the PP, and what I would think is reasonable/normal wear on the fingers given the contact w/ the soft metal on the slave cylinder maybe?


Here's the new one:



Anyone seen one fail like this before? I'd really like to know the cause since 15k miles (even w/ hard driving) seems like a short life for a throw out bearing. 7k miles N/A, 7k boosted @ 630whp, and maybe 1k boosted @ 900whp.

timd38

Just a guess, but if the stackup of the new clutch is greater than the old clutch, it may blow the bearing apart.

Did you call the clutch manufacturer for ideas?

turbotuner20v

They say it should work specifically with the oem slave and master cylinders i have and I know many people run this clutch like that.

turbotuner20v

Anybody have any thoughts on why it failed?

6Speeder

Mine failed on a 2007 Z06 running a Katech LS9 clutch package. It started by making an occasional squealing noise, then it was all the time, then the clutch pedal didn't "feel" right. Pulled it, some bearings missing, plastic melted. Best guess is heat related. It had been in the car for less than 10,000 miles.

turbotuner20v

Did you replace it with a stock one w/o changing anything else? How's that one doing?

pit-man

I don't usually get into these discussions because of all the back and forth arguing that starts up. You ask and here is my guess (and only my guess).

I am wondering if you had the correct spacing on the slave to begin with and it was constantly turning against the pressure plate fingers, causing tons of heat.
I went thru 7 racing seasons and 4 clutches before I even knew there were spacers to be bought, and that each clutch\slave needs to be measured.

My buddy in Colorado installed the same clutch as me...he didn't need spacers and I did. Tick has a nice write up on how to measure before you put that puppy back together. They sell different sizes in a pack.
I made my own and the new clutch is working great and has pulled a 1.49 sixty foot so far. I am having to learn how to launch a single disk again after using dual for all these years.

This is the TICK write up.
http://www.tickperformance.com/tick-...nder-shim-180/



This shim, if needed with your setup, is made here in this USA of .180" thick steel. Will not fit Cadillac CTS-V. Also sold as part of a convenient three pack, here: Tick Performance Slave Cylinder Shim Kit (3 Pack)

How to determine if a shim is needed for your setup:

During each and every clutch install you perform on a newer GM vehicle, you must measure to see if a shim is necessary for proper installation. This is done by taking two simple measurements (see worksheet):

1) Measurement "A" is the distance between the surface of the bellhousing that meets the transmission to the tip of the pressure plate fingers. To get an accurate measurement, the clutch must be torqued properly.

2) Measurement "B" is the distance between the throwout bearing surface to the transmission surface that meets the bellhousing. To get an accurate measurement, the slave spring must be removed and the bearing must be fully seated at the bottom of it's travel; resting on the slave's base.

Once you've got your two measurements, make sure that measurement "B" is ~1/16" to 1/8" LESS than measurement "A". If you come up with more than 1/8", add an appropriately sized shim between the slave cylinder and the transmission in order to get the measurements where they need to be.

Your “A minus B” measurement should be 0.125 to 0.200 for adequate bearing travel and to allow for clutch wear. If there is no difference between the two measurements, or if "B" is greater than "A", there could be a problem with clutch engagement which could result in premature clutch slip and eventually a total failure. Contact your clutch manufacturer before proceeding with the install.

pit-man

some shots










She releases without any gas, smooth as silk. Tex OZ 700

http://s895.photobucket.com/user/Pit...22_74.mp4.html

RicK T

They do fail, not often, but they do. Consensus is it is a combination of proper setup, too much heat and/or just parts failure to be expected sometimes.

Here's a discussion from last year I thought was interesting:

http://forums.corvetteforum.com/c6-z...r-failure.html

turbotuner20v

I can understand the part about not wanting to pre-load your pressure plate fingers which would cause the clutch to never be fully engaged and slip and cause wear/heat/damage to the clutch disks. This would be the A = B, or B > A scenario mentioned at the end of the Tick write up I believe.

As far as making sure A minus B = .125 or .200, how vital is that on a system that will have the spring reinstalled? The spring will always push the throw out bearing into the pressure plate fingers, so it is always riding along w/ the rotating assembly. Adding that shim would help make sure that the clutch disk fully disengages when you push the pedal, but by adding that shim you're pushing the throw out bearing harder into the pressure plate fingers (if the thought is that this heat causes the failure).

Based on the driveablity of the car I'm 99% sure I am not preloading the PP fingers, because there is no clutch slip. Also, I'm 99% sure that my slave cylinder doesn't need to be shimmed because I have no issue disengaging the clutch for 7,000rpm shifts.

I am interested in the 'heating up the throw out bearing causes it to fail' aspect though. I agree that excess heat could lead to the failure, but if it's designed to ride the PP fingers w/ the spring applying pressure at all times (plus hydraulic pressure when disengaging), wouldn't it be designed to handle this, or what introduces the extra heat?

timd38

I happen to be on the same page as Pit-man. I think there is a shim issue as well, because of the damage.

turbotuner20v

Interesting, the guy on the 2nd page had a similar half circle plastic chunk break off:

turbotuner20v

If I add the shim, that's just going to get the slave and throw out bearing closer to the pressure plate fingers. It would seem like being too far away would be easier on the bearing since the spring pressure against the pressure plate fingers would be the lowest, but it would still be spinning with the rotating assembly, so no sudden 'spin up' when I press the clutch and the PP fingers are disengaged.

Perhaps my LS3 slave cylinder is too large for the dual disk clutch and I need the LS9 slave cylinder that is shorter. It would almost be as if my slave cylinder was over shimmed in that scenario. I'll call mcleod to double check. I'm almost 100% sure it's designed for use w/ the stock LS3 slave and that's how everyone on the forum runs them.

turbotuner20v

Mcleod just confirmed again that it's designed for the LS3 slave cylinder.

pit-man

I see where you are coming from...shims would cause more friction on the slave if you already had that problem. I would still measure and confirm that your A\B measure is correct.
If the problem was as I first thought, and you were staging, holding the rpm at 5k+....you would start to creep forward very slowly. Obvious sign the clutch isn't 100% disengaging.

Hopefully someone has had the identical problem and will step in. Sorry I couldn't help.

turbotuner20v

Yea, and I think I'd have a lot more trouble with those 7k rpm shifts if the clutch wasn't disengaging properly. I may rev it up in neutral next time it's on the lift and see if I get any wheel spin just out of curiousity.

Based on that other thread, it sounds like sometimes they can just go out for no reason. Between all the road course, 1/4 mile and street activity this car has seen, I guess it wouldn't be unusual for it to go bad perhaps. If this current replacement goes bad though, I'd like to have a list of things to check out vs. just doing a replacement.

pit-man

You probably need to rev it with the clutch depressed like you are staging and over 5k to see if it creeps. My last clutch was not disengaging completely, but it would still pull some great shifts till it heated up. I would get away with a couple passes, shifting beautiful at 6800 rpm. It wore out real quick.

pit-man

This was my first pass on the new (last clutch) while in Bowling Green. Watch it creep forward, even at lower rpm.

http://s895.photobucket.com/user/Pit...AVIDV.mp4.html

Katech_Zach

I've seen many fail like that. Usually in road racing conditions. Something changed with the OEM supplier. I suspect the grease melts out of it and overheats the bearing. It melts the plastic slider and at that point you start getting fluid leak, spongy/dropping pedal, and disengagement issues. This is part of the reason we designed our upgraded clutch hydraulics.

turbotuner20v

doh, yea, I meant clutch depressed/in gear