Slave cylinder was leaking on my ’01 Convertible @ 80k miles, so I figure while I have it apart, it only makes sense to change the clutch, too. There was nothing really wrong with the clutch previously, just didn’t want to eventually have to do the job twice. Little did I know I would anyhow….

Replacement #1
Buy GM Z06 clutch kit 12570806 (flywheel, disc, pressure plate) and GM slave cylinder 24264180 from Summit & install a National brand pilot bearing
The pins on the flywheel didn’t line up with the pins on the pressure plate, but the bolt holes were fine, so I discarded the pins and installed the clutch (per the advice of Summit’s tech support)

Slight shake at idle and a vibration at 3000 rpm and above. CRAP

Pulled out the clutch and compared everything to the original parts. Flywheel was the same casting number as the original flywheel, but it had a LOT of balancing holes drilled close to each other on one side. Hmmm… must have an out of balance flywheel, and it was a little odd with the pins not lining up.

Then I also notice that the crappy National pilot bearing had failed already (<150 miles) and the bearings were all bunched up along one side. WTF?

Replacement #2
Resurface original flywheel & order Centerforce Dual Friction disc/pressure plate kit. Buy OEM pilot bearing. Everything was installed as carefully & perfectly as possible. The flywheel was aligned to its original position. I even pulled out the polishing wheel to put a nice finish on the pilot of the propshaft. But…

This thing STILL has a shake at idle and a vibration at 3000+ rpm. There’s a noticeable vibration at highway cruising speeds, too.

NOW WHAT!? Nothing else was changed. I’ve installed 2 completely different flywheel/clutch/disc/pilot bearing combinations and they both have the same vibration that was NEVER there previously.

Dave

 

There have been cases where this has happened and it was found that the new clutch/flywheel needed to be match balanced to the original. Not sure how much off the original is now that it was re-surfaced but a check on the original balance to the new might provide some insight.

Do a search on match balance and I think you will find a lot of information on this.

Hope you get it sorted out

 

I had the same issue on the first clutch assembly change.

Fortunatelly the OEM flywheel was in safe place...and was measured out of balance, or more accurately was used to balance the engine.

The new flywheel was match/balanced and issue was terminated.

Here are pics of the OEM Flywheel in my 2002 engine:





Christian

 

dowels don't fit? pics? never seen this

 

Yup. Put one dowel on, the opposite one is off by about 1/2 a hole. I'll take pics. The pressure plate from that kit fit my original flywheel just fine. Figured that was evidence that the new flywheel was totally jacked up.

 

There are sometimes balance weights in the holes around the perimeter of the flywheel. Are you sure they remained after you swapped the original back in? Are you sure the original is clocked the same now as the original install.

Others have posted here that they start with some weights and do a trial and error installing weights in the balance holes until they eliminate most of the vibration. When doing this, I'd think at least having one of those touch vibration meters to measure the amount you changed it would help.

 

sounds like summit boxed the wrong part

as always, need PART NUMBERS and pics to narrow down the variables

the info on FW's being balanced has come up in the past

Although, did GM build LS1's with the transmission in mind and did they leave the engine build plant with auto or manual FW's bolted up?(not going to fix your problem, but would be interesting to know)

 

I bought the GM Z06 clutch, disc and flywheel from Summit with a GM pilot and everything aligned up good with no problems. I feel for you as this has always been a fear of mine. That's why I bought stock replacement parts. Something just doesn't sound right.

 

Balance weights are all in place on the stock flywheel, along with the corresponding green paint marks indicating where they go, and the corresponding paint marks on the pressure plate indicating how much weight to add (the factory clutches were balanced as a set).

Part numbers were listed in this post: http://forums.corvetteforum.com/1582249930-post1.html

The boxes rec'd were GM-labeled boxes, not Summit packaged

The flywheel CASTING number on the goofy flywheel was the same as my OEM flywheel. The barcode on the goofy flywheel was also the same as my OEM flywheel.

That's why I bought those same parts. Didn't want to do it twice. Now I'm digging into it for a 3rd time.

Top Photo: The ZO6 Clutch Kit Flywheel. LOTS of "balancing" holes drilled along the one side. Nothing like my OEM one.
Middle Photo: One side on locating dowel
Bottom Photo: Dowel holes winking on opposite side

 

Just replaced my 02Z with the same genuine GM parts, flywheel/pp/disc Part#12570806, slave #24264180 and p.bearing #14061685. No excessive balancing holes drilled in the flywheel and the dowels lined up. No vibration whatsoever.

 

Do you still have your factory stock pressure plate also? I take it the factory FW is what is on the car now, along with the Centerforce Clutch.

If you haven't come across this thread yet, please read:

http://forums.corvetteforum.com/c5-t...lywheel-2.html

here are some links that are internal to that thread:

http://rumors.automobilemag.com/buil...er-135311.html
http://www.gmpowertrain.com/pbc/
http://www.camaroperformers.com/cama...r/viewall.html
http://www.corvetteclubofamerica.org...ection%203.pdf
http://forums.corvetteforum.com/c6-z...-tour-wow.html
http://www.superchevy.com/technical/...9/viewall.html
http://jalopnik.com/5371569/how-we-b...a-corvette-zr1
http://www.chevyhiperformance.com/te...s/viewall.html
http://www.iwsti.com/forums/off-topi...9-ls3-ls7.html
http://www.popularhotrodding.com/tec...r/viewall.html
http://www.chevyhardcore.com/news/th...y-small-block/
http://www.superchevy.com/technical/...y/viewall.html
http://www.motortrend.com/features/1...d/viewall.html
http://www.chevyhardcore.com/tech-st...he-ls9-engine/

they describe the engine post assembly hot balancing procedure currently done on manual transmission vettes. I believe I included one that was later (2002?) and was specific to LS1/6. There is much more information available now on "them internets" than there was back in the beginning of the C5. The point being, the process is very well described today with the Wixom Perfomance Build Center, and the balancing process has been done since the C5 manual transmission vettes

It's simple really, manual transmission vettes are extremely sensitive to very small engine/FW/clutch imbalances, even imbalances that would still be acceptable for the engine alone. All LS engines are INTERNALLY BALANCED by design. LS engines to be used in manual transmission vettes are then taken a step farther and EXTERNALLY FINE TUNE BALANCED for harmonics to minimize vibrations felt by the driver.

Your factory FW and clutch were not balanced together as a unit. As is the same case now, the FW is delivered from the supplier having been balanced to within xx.x oz·in, and the pressure plate is delivered from the supplier balanced to within xx.x oz·in. That is where the FW gets its partially drilled holes you mentioned, from the supplier. Balance weights are put into the FW if needed only after the FW/PP is mounted to the crankshaft. The balance weights are added to the front damper and FW as needed to fine tune balance the TOTAL ENGINE ASSEMBLY. The balance of your factory FW/PP as a combo match up with your engine internals to create a total assembly balance to within acceptbale specs. If you want to repeat this, you need to have whatever you put on matched to whatever you took off. Not just the FW alone, and not just putting on a zero balanced FW/PP combo.

If you are going to do anything about this now, you will probably be pulling it apart again. Have your stock FW/PP combo checked for balance as a unit and match balance whatever combo you decide to use to the original state of balance. You could experiment with balance weight placement iterations and/or washers under the PP bolts without having to take it all apart again. It's just a matter of how much work you want to go back into.

Again, I'm just trying to help make vette owners aware of the external fine tune balancing procedure done by GM and how it can have an impact on clutch swaps.

Good luck with whatever you decide to do and please keep this updated.

 

Interesting.

 

Yes, stock flywheel with the Centerforce clutch. That combination SHOULD result in a factory-balanced condition, assuming the centerforce clutch isn't messed up.

Here's the kicker....
Running the engine with this combo, with the torque tube disconnected so it's just an engine with a clutch assy attached, results in very little vibration. Just the flywheel and it's even better. Smooth as silk at 3,000 rpm.

 

You are on the right path. However, your stock FW with the Centerforce clutch does not necessarily match your stock setup. It could, it could not, it could be close, it could be way off. "Way" being a very relative term. Remember, these are very slight imbalances that can show up as vibrations. In a perfect world, having a zero balanced FW and a zero balanced pressure plate would mean just that, they are exactly zero balanced. They would have 0.00000000 oz·in imbalance (to however many decimal places you like). This of course is not the case. They are zero balanced (balanced) to within certain allowable imbalance requirements. Each piece has its own balance tolerances. Put them together, and you get tolerance stackups. It is impossible to know how your stock PP compares to the Centerforce PP with respect to balance, unless you measure their respective states of balance. Your stock FW was put together with you stock PP and then put on the engine and then fine tune balanced by putting weights in the FW only (at this engine plane). Therefore, to keep the factory balance of the entire assembly, your FW is only matched with both your stock PP and your engine internals. You are'nt changing your internals. You kept your stock FW. The only component (related to balance) you have changed is the PP. If it is different from your stock PP, then the whole assembly is different. And it only has to be slightly different to notice vibrations. Which leads to your second point;

The "kicker" makes perfect sense actually. Again remember, this fine tune balancing is not done to correct crappy engine balance or anything like that. That is a common misnomer. The same parts and components are used in the engines for manual transmission vettes as are used in the ones for automatics, and engines designated for other vehicles. All C5 and C6 corvettes are different in the fact that they have their engine and transmissions separated and attached via a torque tube. The torque tube is the main vibration culprit here. It is essentially a resonance structure with excitations in normal engine speed ranges. This is true with both automatic vettes and manual vettes. Manual vettes, however, have their gear shift attached/connected to the torque tube. Now the vibration path goes directly into the cabin of the vehicle. There is not enough vibration isolation and/or damping to keep vibrations to what they deemed an acceptable level with the current acceptable total engine balance.

Soooo....
Engines designated for manual transmission vettes are put through a final, finer balancing procedure, which is described at some place in all of those links. When you are running your engine with the torque tube disconnected, you have removed the vibration transfer path. Your engine is fine, and is still fine when you reconnect the TT, but now you can feel vibrations. Does this make sense?

If you already have the TT down, it's very little work to get the PP and FW back off. If you want to eliminate the possibility of your FW/PP as a cause of the vibrations, take them and out, put your stock PP with your stock FW and have it checked to see what the balance/imbalance is. It will be xx.x oz·in out at xx.x degrees from some datum. Then have whichever combo you choose to put back on matched to the original as closely as possible.

Everything I have said above assumes that the vibrations are not coming from something else, ie; damaged or worn TT couplers, damaged TT, damaged throw out bearing, etc....

I truly hope this helps and hope you get it fixed. It sounds like you are fully capable of doing all this yourself, and still have your stock pieces, so you are in a very good position to get it fixed.

 

Took things to a balancing engineering firm today. Real engineering firm that designs & builds balancing equipment, primarily for the auto industry.

They:
1) Measured the original flywheel alone
2) Measured the original flywheel with the original pressure plate
3) Measured the original flywheel with the Centerforce pressure plate
4) Balanced the original flywheel to match the condition in #2

Comments from the engineer I was working with:
This (#2) must be an externally balanced engine. There is a lot of imbalance.

With the Centerforce flywheel, the phasing was off 45 degrees, and there was roughly one in-oz of imbalance, iirc. Took a bit of doing to shift the phasing, but they managed to match it to the original.

DIDN'T WORK

Got the clutch installed (yes, I'm 100% positive that it's in the original position relative to the crank). Fired it up like that and it didn't seem as smooth as I would have expected. Then hooked up the torque tube and fired it up again. Quite a bit of vibration both at idle and at 3k rpm.

Think I might drag the thing out of the garage and set it on fire. Anyone know a safe place to hook up a tow strap?

 

Did you have the tube attached or removed from the bellhousing when you did this? If you tested without the torque tube and it did not vibrate, you answered your own question. Bad driveline couplings. I replaced my junk coupling with the six shooters. The cheapest place to buy then anywhere is KMJ performance in Iowa.

 

imho, it's implausible to think that the driveline couplings suddenly went bad at the exact same time that the clutch was replaced.

 

I would trust that they did a good job at matching, you seem to be keeping on top of what they would be doing. You know that your original setup with its known "imbalance" was smooth when installed, so matching it can help eliminate it from the equation. Have you looked at your couplings and such? Did the engineer you worked with agree with the logic of match balancing, or did he have a different opinion?

 

Yeah, he agreed with what we were doing and I sat there watching through ~80% of the balancing process.

 

What's the state of the car now, is it all back together at this point? What do you pplan on checking or doing next? Did you look at the couplers while the TT was down? I agree, kind of improbable that they failed at the same time as the clutch swap, perhaps they can be damaged during disassembly?