Can anyone help me to understand how thee DM Flywheel works, and what are the characteristics of it being excessively worn?

 

The LUK is a spring-based dual mass flywheel. The bottom line is that shock absorption (or smoothing the engagement of the clutch) in a dual mass flywheel is performed by the flywheel, so a solid clutch disc is used. The LUK unit has springs; the Fr. unit has a rubber center to accomplish the shock absorption. When the clutch is released, the pressure plate sandwiches the clutch disc against the flywheel; the engagement is "dampened" by the spring action (on a LUK) which permits a certain amount of rotation (15mm I believe is permissible on a non-worn flywheel - the workshop manual goes into this) - otherwise the car would be tough to engage smoothly if it were a solid disc with a solid flywheel.

A solid flywheel has a spring-centered, or rubber centered clutch plate that smooths out engagement.

Does that help? For a complete teaching, see the workshop manual since it actually goes into rebuilding the flywheel.

PS I think the dual mass flywheel is called that also because it weights twice as much as a standard one!!!

 

If IIRC in older engines I used to build with these it was always a large outer hollow casing, with a silicon filled and metal weighted section in the hollow part, as the mass rotated teh vibrations were damped out by the internal mass i.e. silicon and metal balancing parts,
The energy absorbed by the mass being "jiggled" (good engineering descritption here) would be dissipated as heat, that is why we had some of ours fail...mind you ours were 4 ft in dia....There designed to dampen the mass being rotated between cylinder firings, i.e as the crank speeds up and slows down, small nuances yes, but noticable in some instances through the drivetrain etc.

kevin

 

Great reply Garrett, many thanks. My C2 has a small amount of transmission backlash that is noticeable sometimes in 1st and 2nd gear. The clutch is well past its best, so I hope that will be the solution when time comes for a change.
1. Has anyone else encountered this irritating fault?
2. What was the original clutch problem with the 964? I had heard that the DM flywheel would come apart?
3. When it comes to clutch and flywheel change time which manufacturer is the best to go for?

 

#2

There were bad vibrations that consistantly worsened throughout a very short period of time, so I changed it out with the LWF kit. Although I have heard of them coming apart, mine did not. When it was removed, there was a bit of movement between the two masses. I did not take it apart (I don't even know if that's possible) but I do still have the old flywheel lying aroung the shop somewhere. Maybe I could dig it up and find out if it does come apart, so we can see what went bad in there.

Duncan

 

The Freudenbergs look like they come apart fairly easy. When I tried to dismantle the newer style flywheel I didn't have much luk. (I haven't tried drilling...)

 

I think mine is disolving as we speak. I started to get a vibration when first starting the car(91c2-68000 miles- probably original parts)on a few occasions lasting a few seconds over the last two months. Then last week while driving it started to vibrate and I just made the 50 mile drive home. Its funny because the night before after a hard drive I thought I could smell burnt rubber. . Clutch works fine , just a strange vibration, getting worse quickly. Its going to snow soon anyway so i will replace dmf and clutch this winter. Will go stock after considering all writeups. I dont track the car. Doug

 

This is helpful:

PS Jason - nice pun!

 

LUK has a great piece of literature called "Clutch System Diagnostic Guide". Looks like it is literature number "LIT086". GREAT pictures and explanations.

www.lukclutch.com

-no affil...

 

Thanks for everyones help, I think that my car has "gear rattle" from a worn (maybe not knackered) DMF. It will be changed with a new part when the need arises.