calvin

After needing a replacement clutch on my 89, I decided to go with a single mass flywheel conversion.

I got a Doug Rippie Single Mass Flywheel (nodular iron/aluminum ~14lbs) and a CentreForce DualFriction clutch. I had a shop balance my new flywheel against my old dual mass flywheel. Once installed (finished yesterday), the setup seems to be great! My engine winds up faster, appears to be more responsive and the clutch feels great.

However, I have one big concern: VIBRATION! I am guessing that my flywheel is not properly balanced (but I'm no mechanic). If I fully depress the clutch and rev the engine, I notice a body-shaking vibration above about 3500-4000rpm. I assume that this is not a problem due to the clutch not fully seating yet (I only have 60miles on the new setup so far) as I believe that when the clutch is fully depressed it should only be the flywheel and the motor that could generate the vibration.

This time I am going to properly seat my clutch/flywheel for 400miles before giving it full throttle (I neglected to do this last time), so I have not gone over 3000rpm with the clutch out yet.

What could be causing this vibration? I am concerned about driving it for fear that the vibration could affect the new clutch/flywheel mating.

If the shop balanced the new single mass flywheel against my old dual mass, I would have expected the same vibrations to exist previously with my dual mass. Only rarely would I ever get vibrations with my previous dual mass, but 99% of the time I wouldn't have any.

What is the solution? I am worried that the only way to do this properly now would be to get my engine pulled and have it rotated to balance with the flywheel. I just spent Cdn$3000 to get my new clutch/flywheel! Argh.

PLEASE HELP! (My shop is closed for a number of days for a race weekend)

Many thanks,
Cal.

RU4L98

Calvin:
Sounds like your problem is not the FW balance, but rather it's position on the crank. The L98 is neutral balanced on the H-Damper, and counter balanced on the Flywheel/Flexplate.

I'm guessing that you didn't mark the location of the old dual-mass unit on the crankshaft?

The OEM Luk FW is cast with a large +/-1Lbs. crescent shaped counter weight. It is then fine/high speed balanced with small weight slugs, which are pressed in near the outer circumference.

And yes, that vibration scares me too! That much imbalance will most certainly cause premature failure in the Trans/engine.


[This message has been edited by RU4L98 (edited 07-27-2001).]

calvin

Hmm... I would be very surprised if my shop made a mistake like that (not marking the crank to match the flywheel reinstall), but I suppose it is possible.

For now I am going to keep the RPMs under 3000 until I can take it back to the shop.

Two questions out of this:

1) Is there any way that this is just a temporary thing and that this is "normal" for a little while in break-in? (ie. is my shop likely to tell me this?)

2) Do you think that your scenario is more likely than the shop having balanced the new SM FW against an out-of-balance (with respect to my engine) DM FW?

Thanks,
Cal.

bill mcdonald

you cant mess up the crank shaft to flywheel, there is a stud to alighn it.

However, I had a flywheel balanced over and it was way out of balance.

calvin

At this stage, how does one correct this?

I am worried that it will require an engine removal... please say no!

bill mcdonald

my engine was so out of balance at 4000 rpms and reving with the clutch in, my drink which was on my cars roof, walked across the roof panel.

1, no a clutch does not break in. if it is wrong at start up, it wont get better.

2, IMHO it is most likly the shop coul dnot get the balancing right.

I did my flywheel swap right after I did an engine rebuild (It was balanced with a dual mass which failed on the new motors first start up) I had shop transfer balance the single to the old dual mass. It was so bad I pulled the engine out and took it back and made them balance the whole thing again.

He explained to me why it is so hard to transfer balance when you have a dual mass, he said it is mostly a guess.

Good luck, another point, the pressure plate usually needs to be lined up with the flywheel, if you have a centerforce clutch it has a yellow painted tab to line up correctly.

one more tip, my engine builder put a card on my single mass which said to turn the flywheel clockwise (I think) then tighten it. I guess the DRM flywheel has a hair of play in it.

Anyhow, I am back with a dual mass flywheel.
Sorry I am not more help, good luck

[This message has been edited by bill mcdonald (edited 07-27-2001).]

bill mcdonald

to be honest I dont know, but for me, I pulled my engine out and had them rebalance it.

However I have a modded engine, much larger rods which weigh more etc... So I HAD to pull the motor.
Isnt the flywheel suppose to be fairly close to balanced out of the box from DRM?

RU4L98

Oops sorry, Brain Fart, I forgot about the alignment pin in the crank.

Could the new DRM FW have more than one possibility of lining up with the crank since it's aftermarket?

Chris

bill mcdonald

Mine had only the 1 pin hole in the DRM flywheel for the alighnment.

zrchris

You're all barking up the wrong tree. The Centerforce weights are the vibration source. I have a ZR1 with that and have the same problem, as did a friend of mine. LPE stopped selling them because of this.

The weights are a gimmick, but also a source of trouble. Remove the weights. You'll have the same clamping force and no vibration. The pressure plate spring is the source of enhanced grip. This is clear to see as the clutch harder to push than stock even without the car running, and about the same effort at high RPM.

Chris

[This message has been edited by zrchris (edited 07-28-2001).]

MarkBychowski

I have exactly the same problem with my Fidanza aluminum flywheel setup. After first finding the problem, I pulled the FW and took it back again to rebalance. It was dead on with the original unit. After numerous conversations with several shops as well as a trustworthy GM Corvette specialist, it appears quite possible that the flywheel is correct and the problem is with the motor. The GM guy told me that he's seen similar problems with factory engines being slightly out of balance. Aparently, the huge factory dual-mass flywheel is able to dampen out much of the vibration, but the light aluminum one doesn't. Regardless, it appears the only solution is what Bill did: get the entire rotating assembly balanced. My vibration isn't too bad, so it's going to wait until I'm ready to rebuild the motor.
I'd be interested in hearing what everyone thinks of what GM told me.

bill mcdonald

I agree with the pressure plate being a gimmick but, I have all those weights on my pressure plate still, My engine is balanced and I spin it up to 6K over and over everyday.

Also the centerforce pressure plate is rumored to be a stock OEM pressure plate. It does not feel any harder to me to push then the stock unit.

crznL98

I'm not sure if you guys have come to a consensus yet as to what the problem is, but, Calvin, have you asked your balance shop if the dual-mass was preloaded when matching the single mass to it? The dual mass's two disks have about 1/2 - 1 inch (around the circumference) of possible rotational seperation. So, in addition to the firt question, "have you asked your balance shop if the dual-mass was preloaded when matching the single mass to it?," how MUCH did they preload the DM, and was that much preload where the factory balanced it? Well, I though I was helping, but I think Bill McDonald might be right, as I don't know of any way to figure out how much to preload the DM. Any way, good luck.

Keith

zrchris

Bill- the Centerforce is a Valeo pressure plate, but with a stiffer spring. If you would drive other cars with stock pressure plates, you would see the pedal is stiffer with the Centerforce. The Centerforce DF is even stiffer than the Centerforce I. I knew a guy that kept breaking forks at the pivot because of the excessive force of the DF pressure plate.

I don't always see the vibration in my car, it varies day-to-day. Others see the same thing with this pressure plate. And again, LPE stopped selling it because of this. Perhaps only if something is slightly off balance is this seen, but it is only seen above 4000, and is not seen with the weights removed.

Calvin- You can do what you like, but when it takes little effort to remove weights and try that vs. ripping your motor down, I'd remove the weights first.

Chris

bill mcdonald

Hmm, Thats strange, I have a centerforce DF, the clutch feels like butter. My buddy has a stock 90 as well, they seem the same to me. I also have a friend with a stock 96, I drive that car a lot and they all feel the same as far as clutch pressure.
I wonder if Centerforce changed thier design? I picked this clutch up in 98.


<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:[/color]<HR><font face="Verdana, Arial" size="2">Originally posted by zrchris]
Calvin- You can do what you like, but when it takes little effort to remove weights and try that vs. ripping your motor down, I'd remove the weights first.

Chris[/color][/QUOTE]
I agree here, and also make sure they lined up the pressure plate (yellow tab) with the flywheel too.

calvin

Well, I have finally resolved this issue...

All in all I am VERY happy with the new acceleration and responsiveness!

Thanks to everyone for their responses. I mentioned each one of them to my shop.

After spending quite a bit of time discussing it with my shop (who specializes in racing Vettes), I now understand the issues a little better.

The dual-mass flywheel would have in fact dampened out most of the harmonic vibrations that would have been present in the engine, differential spline, etc. Not so much the balance itself, but the extra weight would help smooth out the smaller vibration elements. When one reduces the rotating mass by such a large amount, every vibration source will no doubt be felt.

My vibration is actually very little. Previously, I had been driving it carefully, and assumed that if I felt it at 3000rpm, it would only get massively worse if I ran the engine up to 5000rpm (thus I never ran it over about 3500rpm). As it turns out, the vibration seems to be there, but it does not really get much more noticeable at higher RPMs. The problem was that I am very sensitive to little changes in the car and had not expected ANY vibration. When I felt some, I had assumed that it was much worse than it was.

The car accelerates MUCH faster!!! After having raced the car for a while, I can without a doubt say that the increase in acceleration surprised me.

FYI, the balancing was done by a shop that specializes in FW balancing (they do $100k motors). My dual-mass was due for replacing as it could be rotated about 1/2" by hand (springs lost their effectiveness). My shop has had problems with the CF DF II clutches, but these were with the weights coming loose, not vibration. My SM FW match-balancing was done WITH the new clutch. The FW orientation couldn't be an issue as it would be hard to install it wrong by design.

The guys at my shop are going to do the same conversion on their L98s after seeing the difference on my test car. I am interested in seeing the differences on my 0-60.

As for the vibration and wear issue: yes, I know that a little extra vibration will increase the wear, but this is part of what I accept in racing my car. There are many other elements that see high wear in my car, and I know that someday my 110k mile engine will need a rebuild. At that point I will probably go large and try for a strong build-up that will help me keep up with the other high-power cars.

Thanks for everyone's help!
Cal.

95vettski

calvin

That's great news, glad you sorted out your problem. As I mentioned in another thread click hear to view I also have a vibration issue.
The tranny is out and I will have the flywheel balance checked again. If it checks out fine within the acceptable +/- grams I don't know what to do.
What clutch are you using? I'm considering switching to a McLeod clutch with a sprung hub, to help dampen some of the noise.

bill mcdonald

Calvin, Im glad your problem is fixed, I think...

I am confused, I read your post to 95vettski's topic, Do you actually have vibration or a grinding sound?

You said it was only vibrating at 3500+.
Then you said you only took it to 3500 rpms (not over).
then you said in 5th and 6th it is vibrating at 1500-2000 rpms.

this low RPM noise is common with a single mass. That is why I ask.

Back to the vibration, you said it does so at 3500, and remains the same all the way up to red line? How bad is the vibration?

My friend has an LT4 with a single mass (non centerforce clutch) it never vibrates all the way upto 6K rpms.

calvin

Hi Bill --

I don't get any grinding noise, only some slight vibration. I notice the vibration starting around 3500rpm (in 1st-4th), and initially (for the first few days), I barely went over 3500rpm because I was worried that it would get exponentially worse as the RPM increased. However, after talking to my shop they told me not to worry about the little vibration that I had, and told me to try it up to redline. Since hearing that, I have tried it up full throttle through to 5000+rpm, and the small vibration is going to be fine for me. It doesn't get bad like I had expected it to. In fact, it is only really noticeable if you hold the RPM high (which I rarely do) or feel the shifter itself (but I also have a short-throw ripper shifter). All in all the vibration is actually very little now that I think about it.

As for 5th and 6th: in 6th gear, when I am on the highway, running under around 1500rpm, I definitely can feel some vibration. This is likely from the diff spline and tranny gearing combo, with nothing to absorb the gear meshing (like the dual mass would have: by inertia and damping). So, this is acceptable to me.

All in all I am very pleased with the results... The combo with the new sticky clutch and the much lighter flywheel is GREAT. I could swear that I feel the front suspension unload moderately on shifting into 2nd at WOT, when I wouldn't notice that before!!!

As for the LT4 SM FW combo not feeling any vibration: remember that my L98 is 12 years old (no rebuilds yet) and the engine tolerances are certainly a lot looser than a newer LT4. My shop told me that if I had a newly built engine and there was vibration, then we could assume something was wrong. Also, the LT4 might be balanced differently than the L98 (internal/external/mix?). Of course, if/when I rebuild my motor, I will get the whole combo balanced, and I would then expect no "engine" vibration at all.