This is started as a informational thread following comments in other threads and any posts with further information and/or corrections are more than welcome.

Please however don't use this thread to start a discussion on the benefits or otherwise of a DMF.

What is a DMF?

DMF stands for Dual Mass Flywheel.

A traditional flywheel is a large lump of metal, usually with a relatively high mass which acts to smooth out power and torque from the engine.

A DMF is made of two pieces of metal connected by a toothed and sprung system with damping.

A DMF is designed to reduce transmission gear rattle and ease gear changes.

Another function of the DMF is to provide isolation between the crankshaft and gearbox to reduce torsional spikes.

This is a useful web page, with information on DMFs:

http://www.cdxetextbook.com/trans/clutchMan/clutches/dualmassflywheels.html

This video on YouTube shows a DMF:

This video on YouTube shows a failed DMF:

What cars are fitted with a DMF

A DMF is fitted to the following:

Mk I Fabia:

- VRS (PD130)

- PD 100 models

MK II Fabia:

- TDI models

MK I Octavia:

- PD130 TDI models

- Some other TDI models. (1998 onward typically)

- 1.8T models, including vRS

MK II Octavia:

- All TDI Models

- 2.0 T and 1.8T petrol engined models.

MKI Superb:

- TDI models

MK II Superb:

- All TDI models

- Larger petrol engines.

(If you know others that are or that one of the above isn't post and I'll fix it )

Diagnostics

The following are signs that your cars DMF is possibly gone or on it's way out:

1. Your car "sounds like a mad midget trying to hammer his way out of hell".
   
2. Rough idle, combined with a jerky uptake of drive
   
3. Jerky pulling away
   
4. A large hole in your gearbox with oil pouring out.
   

Many garages will tell you that the gearbox has to come off to confirm if there is an issue with the DMF.

I've been reliably informed (thanks MoggyTech) that if you take the starter out, then you can see the play in a failed DMF.

Also my skoda dealer confirmed to me that there is an inspection hole on the 02m gearbox, which can be used to check the DMF.

It was suggested the price for either of the above routes was about the same.

This means a much smaller bill for diagnostics, so if your garage tells you they need to take the box off at hundreds of pounds to check the DMF, then you know it's time to find a new garage.

Likely costs to replace a DMF.

Typically if a DMF dies you should replace the DMF, new seals and the whole clutch kit at the same time.

The reason for this is that the labour cost for taking the gearbox off is a lot higher than materials and as such you don't want to have to risk pulling it off again.

Under warranty this may not be the case and it comes down to if the DMF has damaged the clutch.

Costs are around the £500 to £1000 mark, depending on who you use to carry out the work.

At present a DMF and clutch kit can cost from as little as £200 (none genuine) to about £600(OEM) although prices will obviously vary with time.

Likely causes of DMF failure and how to minimise the chance of failure.

There seems to be a good number of cases of premature DMF failure on cars reported on this forum and others.

While the DMF (or a certain design of DMF) may be a relative weak point in the drive train, there are some things can increase the likelihood of premature DMF failure.

• Racing Starts
  
• Driving around at very low RPM
  
• Putting a lot of power down from low revs
  
• Sharp and harsh application of the power
  
• Remap (See below)
  

All of these put much larger strain on the active parts of the DMF and can increase the likelihood of an early failure.

Avoiding these where possible and having some mechanical sympathy should reduce the likelihood of problems, but obviously the part is a mechanical items and will have a designed lifetime.

Regarding a remap, it should be noted that a remap can cause the car to deliver more power or torque than the DMF is rated for, which will obviously reduce it's effective life.

This is not a given for all remaps and it should be noted that the quality of a remap can vary wildly.

While some vendors will provide an excellent service, taking into account the DMF and other factors, there are others who may provide a poor quality map which takes no account of these factors and can shorten the life of the DMF and other components. (A search should reveal more).

Hope that helps.

Edited 11 May, 201016 yr by cheezemonkhai

Great write up

Great write up

Thanks

FWIW do you know if there is an inspection hole for the DMF on the gearbox/Clutch area?

I've seen some videos that suggest there is and it's purpose being that you can check for failure without taking the box off at great expense.

Would be useful to have that here so that members don't get charged for a strip down if it isn't required.

Edited 5 May, 201016 yr by cheezemonkhai

Guys - where's the THANKS button?

But seriously, thank you CM

Excellent- many thanks. Particularly liked animation! Do all newer Skoda diesels have this system? Does the 4x4 and Scout for instance?

I suspect the 110tdi in the mk1 Octy has a DMF - I am sure I can hear mine 'chirp' at low speed gear changes.

I think that might depend on the car, and as a plus point I know there is an SMF kit available for it too

To answer the question about the scout/4x4 variants of the Octy II, yes I believe all current skoda TDI's have a DMF, although if you're concerned about this, then obviously ask the dealer to confirm it before you place an order or buy a car.

This means you then have come back on the dealer if they say no and you find the car does.

Thanks

FWIW do you know if there is an inspection hole for the DMF on the gearbox/Clutch area?

I've seen some videos that suggest there is and it's purpose being that you can check for failure without taking the box off at great expense.

Would be useful to have that here so that members don't get charged for a strip down if it isn't required.

You can remove the starter motor and check for excess play on the DMF, but honestly when they fail, you know all about it Sounds like a mad midget trying to hammer his way out of Hell.

You can remove the starter motor and check for excess play on the DMF, but honestly when they fail, you know all about it Sounds like a mad midget trying to hammer his way out of Hell.

Thanks, I've updated the post above with a diagnostic section

I've had 5 go on me, then they changed the gear box and had a new one and now it's getting jumpy on pick up and a rough idle combined with a clicking noise that accelerated then slows after you put the clutch down. I asked as none of the first five sounded that bad or even made any noise, but obviously something is wrong and the symptoms are similar. At least the last one lasted over 20k miles.

Anyway, thanks for the info, it's very good to know it's not a box off job, just a starter off.

Edited 6 May, 201016 yr by cheezemonkhai

The Mk1 Octavia VRS has a DMF too, not sure but I would suspect the Mk1 Octavia 1.8T and 1.8T 4x4 also do.

The Mk1 Octavia VRS has a DMF too, not sure but I would suspect the Mk1 Octavia 1.8T and 1.8T 4x4 also do.

Really? I was under the impression it didn't have one.

If you're sure on that I'll add it to the list.

Really? I was under the impression it didn't have one.

If you're sure on that I'll add it to the list.

yes infact ALL the vw engines that have the O2J type gearbox ie cable change with clutch cylinder at the 12Oclock position use a DMF from 1998 onwards so thats 1.8 20v 1.8 20vT ALL TDI's 90 ,110,130 and also the motors with the DSG gearbox (these ones are particulary expensive and strange looking too)

you can now get a solid replacement flywheel and clutch kit for around £150 on ebay but......... i have heard of people struggling to get replacement clutches to fit these once worn out but then i suppose at that price its not the end of the world

I have decided this is a thread worth stickying, so have pinned it up there. Hopefully over time it can be reviewed / edited as things change and new things get found out, etc,

Mods can feel free to update the list as it goes if I don't get time to

Well, I would but to me DMFs are a work of the devil and as I don't run one, do very little research into them.

If however, something is pointed out to me, and I feel it is worthy of including, I will edit it to add anything in of use.

A very useful writeup. TY.

Thought I would add the following. It is normal to hear increased diesel chatter when you depress the clutch, especially when the car is cold. Some people think this is the DMF failing, but it's normal. The noise is purely an audio resonance picked up by the clutch release bearing when it compresses the clutch fingers. The noise can be quite pronounced on cold mornings.

If you leave them too long they can catastrophically fail. We had one that locked the engine when it went, here are a few phone pictures:

If you leave them too long they can catastrophically fail. We had one that locked the engine when it went, here are a few phone pictures:

<snip>

Eeek... that's a lot of damage to the DMF. What damage was done to the engine/gearbox?

Edited 12 May, 201016 yr by cheezemonkhai

The engine and gearbox survived, there was a little metal removed from the inside of the bell housing. The car was an Octavia MK2 (105hp I think). Nice guide by the way.

Great guide, fella

Funnily enough my Furby is going into the stealers next week to have the DMF replaced under warranty. Asked them to check on the change in engine pitch at idle when the cluch is depressed and 1st is selected. Was half expecting to be fobbed off, however got a no quibble 'we've ordered the parts and will contact you in due course to book it in'!!

Should I expect the clutch to be replaced as a matter of course??

Great guide, fella

Funnily enough my Furby is going into the stealers next week to have the DMF replaced under warranty. Asked them to check on the change in engine pitch at idle when the cluch is depressed and 1st is selected. Was half expecting to be fobbed off, however got a no quibble 'we've ordered the parts and will contact you in due course to book it in'!!

Should I expect the clutch to be replaced as a matter of course??

It's unlikely to be replaced unless the DMF has damaged it.

If you want to replace it and get on well with the dealer you might want to ask them if they could order the clutch/DMF kit and only charge you difference between that and the DMF kit alone. If I remember correctly that kit is a good amount cheaper than buying a DMF and a clutch separately.

Otherwise it is just worth asking your dealer to give you a call when it is off, because if the clutch is not damaged, but fairly worn, then you could replace it and save the labour.

Ta for the heads up CM.

Haven't managed to get hold of the dealer today, so will get on the case. Haven't used these guys before, so can't really say that I'm on first name terms just yet. They seem to have a good rep and a fair following on this forum, so who knows.... :S

great thread . my car's into day its a 2008 1.9 tdi dsg only brought it off them just under a month ago,

hope they replace it at there cost and dont thob me off

Edited 29 July, 201015 yr by vwdan1986

For low mileage drivers (5k or less), is the risk of DMF failure on a Diesel high enough to make a petrol a safer financial bet in the long term ?