Light flywheel 'rattle" question

[phillipj]

My question is why does a light flywheel "rattle" at idle? What exactly is happening internally to create that sound?

Thanks !

Phillipj

[dr914jr]

If it's coming from the bell housing it's probably a throwout bearing. Dose it vary with RPM or is it constant?

[phillipj]

If it's coming from the bell housing it's probably a throwout bearing. Dose it vary with RPM or is it constant?

Only when the clutch is out at idle. I have friends with light flywheels in their P cars and they all make the same sound

[Brad Roberts]

normal.. you are now hearing the tranny. No dual mass to dampen the noise :)

B

[1999Porsche911]

normal.. you are now hearing the tranny. No dual mass to dampen the noise :)

B

It is a normal noise of the LWFW. The LWFW often changes the harmonic balance of the crank and produces the noise due to vibration of the shaft. Technically, this is not good for the crank bearings and the choice you have to make is whether the added performance you get from the LWFW is worth the risk of possible bearing damage.

Edited February 26, 2009 by 1999Porsche911

[phillipj]

Great,

Thanks for all the feedback.

[Brad Roberts]

Tranny noise :)

I have been running the light flywheels since the day Aasco released them (8+ years ago??) and NONE of them have caused any bearing issues. Ever.

The Tilton multi disc clutch we run makes the same noise on the same tranny's.

This is a 6speed 996 tranny. The synchro's are multi part and RATTLE when not dampened. Porsche goes to great length to make sure the cars are "dumbed" down. If I handed you a gear with synchro (covered in gearlube) you could shake it and hear the same "rattle" he is hearing from his car at idle. The gear lube we run today is nothing like what we ran in the 901's/915's/930 boxes. It is much thinner and synthetic. All this factors into the rattle he is hearing :)

Every arrow in this picture points to a synchro. Every synchro is a rattle.

B

[phillipj]

Brad,

Thanks for the great information! It's nice to know what exactly what is happening.

I'm also relieved to hear that you have not had any bearing failures. I love the light flywheel and would dissapointed to have to go back to stock.

The LWFW also makes people (girlfriends, wifes etc) not want to drive your car as well (they don't care for the temprement of the Light flywheel) lol!

:renntech:

[dr914jr]

Noise is friction! Friction is bad, especially if it's coming from the crank. The only way a lightened flywheel would cause noise is if it has thrown the crank's balance off. If it is the flywheel and not the throwout bearing remove the flywheel asap. However my moneys still on the T.O.B. as this is by far the most common cause of "transmission noise".

[phillipj]

I think what Brad is saying is that the noise is there all the time (with either flywheel.) You just don't hear it with the Dual mass. I may be wrong about this so don't get angry :huh:

I have two Porsche friends who have been running light flywheels for 5 or 6 years on their 996's and they track their cars every chance they get.. They drive the crap out of them and have never had an issue with a bearing.

It's interesting to hear everyone's mechanical input. I love this stuff. I think I should have followed in my Father's footsteps and had a race team.. A lot more fun me thinks! B)

[Brad Roberts]

The noise has always been there. Promise. You just don't hear it with the dual mass flywheel. The dual mass is a harmonic balancer of sorts, but primarily for the INPUT shaft of the tranny not so much the crank. The 997's have a harmonic balancer at the front of the crank and the dual mass flywheel.

B

[Brad Roberts]

However my moneys still on the T.O.B. as this is by far the most common cause of "transmission noise".

He *just* had the engine installed with all new clutch/flywheel/TO.

To test if it is the TO: push the clutch in. The noise will go away.

In this case.. with "synchro rattle" it will get worse!! :)

B

[phillipj]

Brad,

Now I'm confused :huh:

On my car and my friends cars the noise (rattle) is there at idle when the clutch is out. When you push the clutch in it (the rattle) does go away and you don't hear any ratlle when in any gear. Are you saying that the rattle should be there even when the clutch is engaged as well?

Does this mean that my TB is bad? Clutch was replaced 20k miles ago and my tech said it did not need to be replaced when I got the new engine. He would have recommended it if it did.

Thanks!

Edited February 26, 2009 by phillipj

[Brad Roberts]

Aasco light flywheel we *all* use :)

B

[Brad Roberts]

Your fine. Sorry about the confusion. Push the clutch in and it the rattle does go away. The TO has a different sound.

I re-read my post and it confused me.. LOL:

When the clutch it out, the input shaft is turning the same speed as the engine, push in the clutch and it slows down and gets quieter.

B

Edited February 26, 2009 by Brad Roberts

[dr914jr]

Hell, Now I'm confused as well. I probably have more miles on my car than anyone here and I've never had a rattle at all. Completly regardless of what I do with the clutch pedal.

[phillipj]

LOL! :D

Thanks Brad..DR914.

So when someone pulls up next to me and says "what's that rattle" I can say "I have no idea.Ask Brad"... :D

[Brad Roberts]

Hell, Now I'm confused as well. I probably have more miles on my car than anyone here and I've never had a rattle at all. Completely regardless of what I do with the clutch pedal.

Do you have the Aasco flywheel? Or the Fidanza? (sp?) there are 2-3 different flywheels. I can only speak about the Aasco and the 20-30 I have installed and the 20-30 cars I work on that already had them installed.

I will admit different gear lubes will increase or decrease the noise. Mobil1 = rattle with light flywheel.

As far as vibration: the Aasco flywheels are *pretty* well balanced out of the box, but not perfect~! The stock flywheel.. is WAY off, but the rubber dual mass dampens the effect.

B

[Brad Roberts]

"what's that rattle"

Tell them it is a race car :) They will go "ohh-ahh" :lol:

B

[phillipj]

Brad,

Is there a transmission lube that would decrease the noise? What are the choices besides the Mobil 1? I was planning on servicing the tranny so it would be a good time to know my options.

I'm not sure what brand of flywheel is in the car. The previous owner installed it and the reciept for the work does not specify the brand. It just says "install light flywheel and clutch assembly". I know it was quite pricey though.

[Brad Roberts]

99.9% of the shops buy/use the Aasco flywheel. Very few even know about the others. You are standing a good chance it is the Aasco. They are the only light flywheel sold by the wholesalers that provide the shops with their parts.

Motul gear lube will quiet it down (don't expect miracles) :)

B

[Brad Roberts]

Thanks Brad..DR914.

Easy now. That title is taken by a well know fellow in Hotlanta :) I claim to know nothing. Easier coming off as dumb than smart :)

B

[phillipj]

Actually I was reffering to the other member who was on this thread. His forum name is "DR914jr" I was not accussing you of being a doctor lol! :D

Thank so much for all the great info. I will look into the Motul product.

[Brad Roberts]

Just so happens, I have been involved with some of the fastest 914 track and AutoX cars in the USA :)

B

[dr914jr]

Sorry I was just kidding. I'm on my second stock flywheel.