69stangscj

iTrader: (3)

I see people talking about switching to the LS7 flywheel, but not sure of the purpose? What does the LS7 flywheel get you?

05CTSV

iTrader: (16)

Lighter rotating mass, no center hub to go bad, improved performance.

A dual mass is just that, essentially two flywheels or plates held together by a spring loaded center hub. The spring rate is that to absorb the initial torque to reduce driveline wear, noise, etc. The center hub can and will go bad over time and begin to rattle. This can cause vibrations, a dieseling effect when turning the car off. Mostly everyone swaps it out for the weight and performance benefit. It all depends on what you want your car to do. When I swapped mine out the stock dual mass, clutch, and pressure plate weighed in at aprox 78.5 lbs. The Monster clutch and single plate flywheel totaled around 46 lbs. I went with a 28 lb flywheel, there are lighter flywheels out there. Also the stock clutch has self adjusting pressure plate fingers that can sometime trip you up at higher rpm shifts. Hope that helps.
Also search YouTube for dual mass flywheel, you'll get a lot of good videos to show how they work and how they fail. Here is a good 3d animation on how they are assembled and function.
http://youtu.be/YnaXB8q3uzQ

meatyCTS-V

A dual-mass flywheel is to keep the revs from dropping too fast while the geriatric Cadillac owners slowly move their arthritis-infused limb to select gears...

BUKSING

iTrader: (2)

Lol that was funny.

69stangscj

iTrader: (3)

Thank you for the explanation. On the self adjust clutch fingers, are you talking about the higher the RPM the more centrifugal force is exerted on the clutch fingers clamping the clutch harder?

gtfodave

what is it? Junk swapped mine out in my old lt4 and couldnt believe i delt with it that long

Stone17

iTrader: (3)

This.

05CTSV

iTrader: (16)

No, many have had issues with the clutch pedal going soft or not returning off the floor. Some not being able to go into gear at higher rpm with the factory clutch and pressure plate. The design of the factory unit was just crap from the start. They put in a high HP motor but tried to keep it quiet and smooth for the typical caddy crowd. Like the one post said, so the arthritis limbs could push the pedal down..LOL.

It's probably one of the best upgrades you can do. There are plenty of aftermarket options from very basic to very extreme. Many choose the LS7 clutch because of price, it's a GM part, and it works well. The only reason to go aftermarket is if you plan on making more torque than the LS7 is meant to handle.

DACTARI

iTrader: (1)

I just went with a 20lb flywheel with LS7 clutch. It's a bit of a challenge to re-learn with a medium/high-overlap cam. The extra mass really helped with low-speed driving. On the other hand, there's the big grin I get when the engine spins up so much faster than it did before. 0-30 acceleration is pants-wettingly improved.

td/dr: i love it, my wife hates it

69stangscj

iTrader: (3)

I’ve experienced the clutch pedal sticking to the floor, but what actually causes that? From what I can tell, the dual mass flywheel just smoothes out the shock in the drive train. The clutch sticking to the floor, would have something to do with the spring force on the fingers of the actual clutch at high RPM correct?

kyle242gt

I believe that's the clutch pedal return spring, but am not sure. A different issue.

Other than the needless weight and complexity, the DMF seems like a cool idea. The clunking as it gets tired stinks though.

Interesting to see the clutch disk isn't sprung on the DMF...

05CTSV

iTrader: (16)

Correct. When you push the pedal down the slave cylinder pushes on the pressure plate fingers disengaging the clutch. When you let up on the pedal the pressure applied to the fingers pushes back against the salve cylinder causing it to return the pedal. From what I've read the issue with the stock pressure plate is that at the higher rpm the fingers don't fully return and leave the slave cylinder fully extended or partially extended depending on the scenario. Not sure if the dual mass really has anything to do with that. In either case the stock setup isn't the best for performance driving.

69stangscj

iTrader: (3)

If that was true I could sit with the car parked and the motor off and push the clutch up and down real fast and it would stick to the floor. Right now, it only happens 6500 plus RPM, GM has a service bulletin for it and requires a clutch/pressure plate change. To me, it would have something to do with the spring fingers on the pressure plate at high RPM. I’m just curious what is happening to them at high RPM.

kyle242gt

Great info, should have considered the engine-off situation. My guess is the return spring is there as a bandaid for the high-rpm lack of PP force.

I wonder if that lack of force is a consequence of the thicker FW requiring a thinner PP, and the resulting geometry of the PP fingers.

My clutch stuck once, briefly, also at high RPM. Naturally I was too busy going "WTF" to analyze the situation fully.

69stangscj

iTrader: (3)

My guess is the flywheel has nothing to do with it. And it would all be in the pressure plate. Another guess here is the centurial force is doing something to the clutch fingers at high RPM.

punishmentcycle

iTrader: (6)

clutch fingers lose their strength over time.. high rpm's cause the already weak springs to stick..there for the pedal gets stuck

meatyCTS-V

Try bleeding out your slave and master cylinder. See if the fluid in the master cylinder is dirty and contaminated.

I've heard that old fluid and dirty fluid can do this, too.