Lightweight Flywheel Chatter
 

To those of you who followed the post a few months ago, I recently installed an Aasco lightweight flywheel and Sachs Sport clutch in my 02 S. Work was performed by a very qualified shop. Since the first time I cranked the car when I picked it up, it has had a decent bit of chatter while in neutral and the clutch up. I've heard from many that this is a normal problem encountered on these cars when doing this mod because you are going from a dual mass to a single mass flywheel in a clutch hub designed for a dual mass. Lately, however, I've talked to a few other techs that I"ve had the car around, and a few of them suspect either a bad throw out bearing (both pilot and throw out bearings were replaced with OEM during the clutch job, along with RMS and clutch slave) or a damaged diaphragm.

Can anyone give some insight on this? Chatter normal, or is something not quite right in my driveline? The clutch actuation is beautiful, and the car drives great.

Patrick

Does the noise go away when the clutch pledal is down it idle?

Yes.

Patrick

well, if the noise goes away when you press the clutch in, then the throwout bearing should be ok, as this is when the load on the bearing is the greatest..

I would probly look at a defective part, or an installation error..

how bad is the noise? we talkin' overly obvious, or you can hear it if ya listen for it?

Yes, the chatter goes away when you press the clutch in in neutral. I would best describe the noise as a true chatter, very similar to the dry clutch on a Ducati for us bike guys out there. Def obvious...

The real problem, is I have absolutely no interest in pulling the gearbox off the car AGAIN to deal with this.

Patrick

bmwm750,

Seems like the chatter is common with the lightweight flywheel :

http://986forum.com/forums/performance-technical-chat/12420-best-performance-mods.html

You might want to PM edevlin and compare notes...

Nick

I've heard this is normal from a few people, but I don't really understand why it would be. The flywheel is bolted to the engine, and simply spins with the crankshaft, so I don't see why you'd have chatter from it being single vs dual mass.

Patrick

Maybe it chaters because of the lack of springs, as in the dual mass flywheel? I would suspect the dual mass is quite a bit better a dampening any chatter, whereas the solid (it is solid, right?) light flywheel has no chatter dampening.

The alu. flywheel is a solid mass,(well aluminum with a steel plate where the clutch contacts it..), If that was going to make noise, sumtin' might be loose...

Exactly. It is solid (alu with steel friction surface), which is bolted to the engine, which all spins as one unit..... so I still don't see why it would chatter, even though I've heard from several that this just comes with the territory....

Patrick

if everything is tight on the flywheel, the noise most likly is coming from the clutch disk or pressure plate....

I have the aasco fly and it has chattered fron day1. I also had clutch done, with new everything when it went in. My porsche mech who did it told me it would chatter before he did it. What exactly makes the noise he was not sure about. He said it is much better in boxsters than in 996's. In a 996 the transmission is between you and the engine, and in the box, the engine is between you and the tranny, this was his reason. My chatter is only noticable stopped at idle, you can hear it, but it isnt what I would call loud. But any "car guy" standing next to the car would immediately know something is up.

I did get a chance to hear a 996 with one in his shop, and it is MUCH louder inside the car than in the box.

I also know that in BMWs with lt wt flys there is chatter. I think it is just inherent to lt wt flys bolted onto cars designed for dual mass flys.

also, I am pretty sure the reason the manufacturers went to dual mass flywheels in the first place was for smoothness and to reduce vibrations in the drivetrain from the drivers perspective. I think Porsche started using them on the 964 and 968.

Regardless of the reason, I can understand why a 996 is louder than a 986 due to drivetrain layout. If the chatter really is "normal," I'll just live with it. Its not obnoxious, but it is noticeable.

Such is life....

Patrick

Light Flywheel Chatter
 

I know this thread is old but I know what the answer is: Transmission gears are rattling against their mated pairs. Removing the dual mass flywheel took away the isolation of crankshaft torsional vibration from the gearbox. At low engine speed compression strokes and then power strokes, slow and then increase crankshaft rotational speed markedly, causing gears in the transmission to bang forward and back against each other making this sound.

When you disengage the clutch (pedal down) the transmission is disconnected and the noise goes away.
Using a driven disc that has a spring hub is the best answer I know of to lessen this noise.

Hope this helps someone.
Randy

As you probably realize, the chattering is just a symptom of uncorrected imbalance. There is no harmonic balancer on the front of the crankshaft so depending on the severity of the imbalance, your engine is experience gross,momentary overloading of various bearings and sundry other items.
The best remedy would be to get a good,used DMF balanced (with the clutch assy)and fit it.
You may be more interested in refitting the DMF if you consider the potential problems that will emerge from ignoring it.
There is lots in Search on this subject.

Forget all that....
 

....once his crankshaft snaps in half, the chattering will stop.

Real sudden like.

I was trying to be gentle.
When we have discussed this issue ,some get really nasty about having the reasons for it being a poor idea explained to them. Even when Jake has gently explained why he does not use LWFW ,we still got unpleasantness. It may require the financial pain of c/s breakage for people to be grateful for such advice. But I hope not.
It is worth noting that some LWFW uses claim no ill effects but they never gave details of any other mods they made to alleviate the problem. Even when we tried to separate the issue for them into harmonic and dynamic imbalance we got grief. In theory ,even a professionally balanced flat 6 will have some (harmful?) vibration w/o a DMF or harmonic balancer.

Having come from the Nissan 350z world I can tell you this is a common problem with the newer cars that came with A Dual mass Flywheel. Cement grinder was more of a descripter of the sound our cars made with Light weight FW. One of the reasons I passed on the idea.