/ Octavia II diesel - DMF, fly in the ointment?

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iksander on 04 Jan 2013
Word to the UKC Octavia posse. What's the deal with dual mass flywheels? When did they stop fitting them? Will SUK really replace them, or only under warranty or good will contribution?
Siward on 04 Jan 2013
In reply to iksander: I've been looking into these because they are an increasingly common fitment to all sorts of, particularly modern diesel, cars including my Saab where its starting to give problems at a measly 65k.

My research concludes that they are a very BAD THING, always fail in any model of car and are an inherently retrograde step in automotive engineering. I'm thinking of reverting to an old saab 9000 with a proper clutch.

Replacing one for a solid version is also a bad thing since the opinion seems to be that its all well and good to convert them but you are inviting gearbox failure within 10-20K thereafter.
Dom Whillans on 04 Jan 2013
In reply to iksander:
i had DMF problems develop in my mkII octavia last year, after 130,000 miles mind you... i replaced timing belt, flywheel, clutch and water pump in one fell swoop for a wallet busting 1100. Bearing in mind (pun intended) the work that needs to take place to get at these parts, i thought it wise to get everything sorted whilst the front of the car was off. fingers crossed i'll get another 100,000 miles out of most of it.
Martin W on 04 Jan 2013
In reply to iksander: Have a look on the Octavia forum on Briskoda.net: http://lmgtfy.com/?q=site%3Abriskoda.net+octavia+dmf (sorry, not being sarky, it's just a clearer URL than the actual Google search one).

A brief scan of the first hit from that search suggests that SUK are replacing DMFs for conventional flywheels on cars which have DMF problems.

My understanding is that DMFs they are becoming increasingly common on modern automotive diesels and even some petrol engines, so I'd be surprised if they actually stopped fitting them unless there was an insurmountable problem with a particular engine - which might be the case for the VAG 1.9Tdi (I haven't read that far).

As whether or not they are a BAD THING: they're obviously one more thing that can go wrong - and unfortunately they are quite expensive to replace when they do go wrong. I believe the idea dates back to the 1980s so you could argue that it's a young-ish technology which still has to have some of the bugs ironed out. The benefits, as I understand it, are that the overall mass of the transmission can be reduced cf a SMF, so the motivation for fitting them is probably reduction in emissions as much as anything. Hence also why a straight swap for a SMF is not necessarily a brilliant idea, as Siward suggests. Presumably SUK are confident in their SMF modification, though - or maybe they've decided it's easier to placate irate owners by replacing their DMF, and hoping that the number of people who subsequently suffer other transmission problems and link it back to the SMF will be relatively small...

(I remember the complaints when ECUs aka "black boxes" first started to become common in the 70s. They often went wrong, and they cost an arm and a leg to replace. They still cost a lot to replace, but they go wrong much less commonly these days. And you pretty much can't build a car that meets modern emissions regulations without an ECU.)
wilkie14c - on 04 Jan 2013
In reply to Martin W: Yea thats how i've understood them, an improvement in fuel economy, decrease of emissions and smoother take up of drive which high torque diesel engined cars need to smooth out drive. The extra cost comes in where a normal clutch kit would be a plate, diaphram and bearing, the DMF is 2 diaphrams and a flywheel <sort of> The later mondeos have the same arrangement as do Fiat doblos, my old fella has one in his mondeo and pricing the parts for him meant he wasn't really saving that much overall and he had it done in a garage in the end, 500 ish. One thing to watch for is folk just replacing the diaphams but keeping the original flywheel and then selling on. If buying a car with a DMF that has had the clutch done recently my advice would be to inspect the parts list of the invoice of the clutch.
A bummer when it goes but they aren't something to be frightened of.
Andrew Lodge - on 04 Jan 2013
In reply to iksander: It seems a bit of an exaggerated problem I think, partly becasue it is a big bill when it does go wrong, my Mondeo did 255k on the original clutch and I know of a lot of others with big miles and no problems
Neil Williams - on 05 Jan 2013
In reply to Siward:

They were one big reason my current car is petrol rather than diesel, given that they tend to fail because of the high torque of a diesel.

Neil
iksander on 05 Jan 2013
In reply to Neil Williams: yes I wonder if an FSI would make more sense for me, as I only do low mileage
monkeys on 05 Jan 2013
In reply to iksander:
Diesel engines did last forever, and they still can, but all the expensive ancillary items like DMF, Diesel particulate filter, turbos give up way too soon. Some because of lack of vehicle empathy by drivers, and others just because !.
Diesel makes no sense for a lot of drivers if you take whole lifetime cost of ownership v improved mpg into account.

Doesn't have to be as cripplingly expensive as it first appears though.
In my experience DMF & clutch at Main Stealer 1500, Independent specialist 800, good independent garage 650 - all with identical LUK or Sachs parts.

Martin W on 05 Jan 2013
In reply to Neil Williams:

> given that they tend to fail because of the high torque of a diesel.

I think you have that the wrong way round. The DMF is used because of the high torque of the diesel (although they are increasingly being used on petrol engines as well). They tend to fail simply because they are mechanical items which are prone to wear, can be assembled incorrectly, or can be built using the occasional just out of tolerance part which gets through the quality processes. In comparison, an SMF is basically just a solid lump of metal.

As Andrew Lodge says, they're not something to be afraid of. They're there for a reason. It's just that, before they were used, they couldn't go wrong. Now they are used, and they can and do wrong - but people have never experienced that problem before, don't like the bill and conclude that the thing which broke must be evil.
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Lord of Starkness - on 05 Jan 2013
In reply to iksander:

The petrol engine was a no brainer for me. I now only do less than 8k per year, so I opted for a 1.4tsi instead of the diesel. Performance wise it knocks spots off my old 53 plate 1.9tdi, yet still gives around 40mpg on all but the shortest of runs. I reckoned that it would take around 8 years for the extra fuel economy of the diesel to justify the extra cost of having a diesel engine. Furthermore there are well documented problems with the VAG Diesel Particulate Filter if you only do small mileages.

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