Dual Mass Flywheel problem?

[matthewb]

Hi chaps

I'm wondering if I have a problem with the DMF on my 97 C4S. It's done 150k and had a new clutch fitted at 90k.

The car has developed a clunk when pulling-away - feels like something's loose. I hoped that a new gearbox mount might fix this - but it didn't.

I read something on the Rennlist forum a few days ago about how a failing DMF can cause a screech when starting the engine (during the actual start and for 2-3 seconds afterwards). I have experienced this a lot during the last 10k but put it down to an oil change (Castrol GTX was accidentally used by my indie rather than my usual Mobil 1). And, apparently, there can also be a clunking rattle when turning-off the engine, which I have also occasionally experienced but ignored.

Posts in the following PCGB forum threads originally got me thinking my 'clunk' might be a DMF-unbonding problem...

• http://www.porscheclubgbforum.com/tm.asp?m=574424
• http://www.porscheclubgbforum.com/tm.asp?m=429360&mpage=1&key=&#432239

Some questions ...

• Does anyone know if the above symptons are indicative of an unbonding DMF?
• Is the flywheel a part of the clutch assembly, i.e. if I buy a new clutch, do I get a new flywheel as well?
• Any idea of how a DMF works? I've tried a few internet searches but can't find any real detail.
• I've read that DMFs really found their home on diesel engines to stop low-rev rattle. Does a Porsche petrol engine really need a DMF?
• If I do need a new flywheel, what about fitting an RS Single Mass Flywheel or other lightweight flywheels?
• What problems could an unbonding DMF cause? Excessive gearbox, engine, transmission wear?
• How much?

I guess this is a problem that we'll start to experience more often as our cars get older.

Thanks
Matthew


P.S. I'll be at the Porscheshop 993 Tuning Tips event in Halesowen on 9 Oct. I get the feeling that take-up of places may not have been as feverish as the last 993 event. I hope lots of us do show-up and support Ken's and Maurice's efforts.

 

[Mark Elder]

Hi, can only answer one of your questions - DMF is not part of the clutch kit, although anyone changing a clutch is going to check out the DMF while in there. My indie said my DMF looked pretty good when my clutch was changed so it stayed put.

Interested in the screech diagnostic - I get a screech, not on start, but when cold and I quickly increase revs, eg when blipping throttle during a change down. I assumed it was a belt, so had them all changed at a recent service, but it is still there in exact same conditions.

I'll be there on 9th - looking forward to it.

 

[matthewb]

Hi again chaps

Here's a selection of bits n bobs on flywheels I've picked-up from the Rennlist forum...

The 993 GT-2 is fitted with a special lightweight noise reducing DMF called the ZMS flywheel...Double mass ZMS version 8.6kg (19lb)

DMF = 13.6kg (30lb)
MWF = 8.6kg (19lb)
LWF = 5.5kg (12lb)

I have the MWF from Andial. It's great, a little noise, but nothing good sounding exhaust upgrade won't cure!

If you are concerned about potentially stalling using LWF I wouldn't even bother with the Andial midweight flywheel, they are way over priced and you can buy a non-machined MWF directly from Porsche, part number 964-102-239-00 $324.67 (available from europarts in UK)

Another symptom of a failing DMF is a vibration at around 4K RPMs that you can usually feel in the shifter.

DMF is standard Porsche fit to stop customers complaining unnecessarily about low-rev rattle.

The shop manual clearly states: "When repairing the clutch, replace only those components that are faulty and avoid replacing the double-mass flywheel if this is still fully operative."

I think a LWF may decrease engine longevity

To check for a failing DMF you rotate the secondary mass 15mm and if returns to its original position it is okay. If you can rotate it more than 15mm or if it just doesn't return or if it doesn't rotate at all then you have a defective DMF.

I'm hoping someone at the Porscheshop bash will be able to confirm or refute my suspicion.

 

[vitesse]

As far as I know,many Dual mass flywheels are currently fitted in various "ordinary " cars like Mondeos,etc & basically comprise a normal flywheel which fits to the crankshaft-this flywheel has a secondary part bonded to it with a rubber type cush drive coupling & the clutch plate engages with this 2nd plate-the effect being to isolate vibrations from engine pulses from the driveline-your post indicates the possible amount of "twist " that is acceptable between the 2 parts.

 

[Taverner]

Mathew,

Became interested in dual mass flywheels and how they work for non porsche reasons and found this on U-tube. Sound did not work for me but seemed to give a good idea as to what they are all about. Hope the link works

http://www.youtube.com/watch?v=YnaXB8q3uzQ

I am also planing to go to Porsche shop on the 9th so maybe will meet you there.

Michael

 

[matthewb]

Many thanks, Michael (and Colin and Mark) - I should have thought of using YouTube - doh!

That was very useful - shame about the lack of commentary, as you say. More complicated than I thought but very elegant.

Here are a couple of others ...

• "Dual-mass flywheel on a Volkswagen Golf TDI"
  http://www.youtube.com/watch?v=Y3mFz6NOmWg
• "ZF zms dual mass flywheel for passanger cars" Interesting voice-over. Sounds like Stephen Hawkins' sister. At the end she says, "ensures high noise and comfort levels". I'm sure she meant "low noise".
  http://www.youtube.com/watch?v=DbvP5EvpUbA

I sort of get the idea. All I've got to do now is get in there and see how much rotation there is. I'm sure my indie will think of a creative amount to charge me

Cheers
Matthew