Dual Mass Flywheels.

[Brian Kirby]

Sorry this is a bit technical, but can anyone please explain, in layman's terms, jut what are the supposed advantages of these? 

I understand they are supposed to contribute to greater fuel efficiency, but by just how much?  Does the saving in fuel costs equal the extra cost of a replacement over its expected life?  If not, what are they for?

It seems they are implicated in a number of driving difficulties, and may have a hand in the infamous Sevel reversing judder.  Am I missing something?

I am aware there are kits available to substitute standard flywheel/clutch assemblies for at least some engines, so presumably they have not been welcomed with open arms by all users!  However, I don't remember seeing many kits to install them in lieu of conventional clutch/flywheel assemblies.  Why not?

It seems universally accepted that the clutch assemblies are far more expensive to replace that conventional clutch assemblies, and it is not clear they last correspondingly longer.  In fact, rather the reverse seems the case.

So, the users seem to experience a number of unwelcome effects from their inclusion in vehicles, with some even spending substantial sums to be rid of them, yet they seem more and more widely specified by manufacturers.  Why is this?  Just why are we being fobbed off with these apparently fragile, expensive, and unreliable items, when there is a perfectly good, tried, tested and satisfactory alternative?  Or am I just being a Luddite again?

[neillking]

I'm no expert on these but came across a few things that made them more understandable ...

"The dual-mass flywheels absorb engine vibrations before they are transmitted to the driveline where they can create gear rattle. The unit is split into two sections: a primary section that bolts to the crankshaft, and a secondary section, onto which the clutch is bolted. The primary section dampens, isolates engine vibrations and prevents engine torque spikes from damaging the transmission." 

and

"(it is a) view of a dual mass flywheel as a mechanical low pass filter that is important here. It isn't the level of torque output of modern diesels that's the problem - at least not in a direct sense, it's actually how suddenly this torque is built up during a cylinder firing event" 

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

[Guest Tracker]

I don't know either Brian but - just like catalytic converters - I believe it is called, by those who sell the ideas, 'progress'?

 

Along with many other 'design' features and 'construction' methods and materials used in 'modern' vans the whole world of motorcaravan and automotive design in general has gone stark bonkers by introducing 'new' concepts before they are fully tested.

 

There are of course very many advantages of newer vehicles over older ones - safer, quieter, smoother, more economical, more reliable (well usually).

 

However I find the current approach of making the consumer pay for the 'privilege' of being the manufacturers final testing process, during which any problems found can be ignored or blamed on the user, thoroughly distasteful and that's why I'm sticking to the well tried and tested old Ducato / Boxer!

 

Some manufacturers are more concerned about their reputations than others, as ever was, and those manufacturers with a poor reputation seem to think they have nowt to lose by making it worse.

 

Sorry it's a bit off topic, anyway - rant over!

[Derek Uzzell]

Brian:

 

I'm not aware that dual-mass flywheels as a breed offer better fuel efficiency, though I guess fuel consumption might theoretically improve if the complete DMF assembly were lighter overall than a 'one-piece' (SMF) equivalent.

 

My understanding was that (as Neillking quotes) the raison d'etre of a DMF was its better effectiveness in damping abrupt changes in a modern motor's (particularly a diesel motor's) power delivery than a traditional SMF, thus allowing greater 'civilisation' and providing shock-protection for the transmission.

 

Replacement of a DMF with a SMF kit is likely to be significantly cheaper than straight DMF-for-DMF replacement and consequently will be attractive where an older/high mileage vehicle is involved. SMF-for-DMF kits are also marketed to cope with increased power outputs when a motor has been heavily performance-tuned and 'civility' is a secondary consideration. I'm doubtful that vehicle owners choose to replace DMFs with SMFs unless they must (eg. the DMF is worn out, broken, or unable to handle a hike in power). Presumably the present relatively limited number of SMF-for-DMF kits suggests that it's not financially worthwhile producing them for a very wide range of vehicles.

 

My Mk 6 Transit's 2.0-litre motor with DMF is much more civilised (and powerful and abstemious) than its uncouth but simpler 2.5-litre predecessor with SMF. If I could have all my current motor's benefits with a SMF rather than a DMF, then that would be my clear preference as I naturally favour simplicity over complexity. But if I knew that changing to a SMF would be detrimental in terms of motor-noise or smoothness, then I might change my mind. It would be nice to have all like the sophistication of a modern vehicle coupled to the simplicity of a wheel-barrow, but that's really not feasible.

 

I'm not sure if yearning for SMFs makes you a Luddite, but it may be symptomatic of Morris Minor-ism. It would be interesting to know whether - should the DMF on your Hobby fail within warranty - you would deliberately opt for a SMF replacement.

[Slim]

I suspect that the DMF is a contributary factor in the reverse judder problem.

There is no doubt that there is less vibration and noise transferred from the engine to the drive chain.

 

I also suspect that different styles of driving contribute to early failure and labouring of the engine would give the DMF springs the worst possible treatment.

 

White van man usually drives at full power and full revs, forward or reverse so the springs don't get such a hammering and probably wouldn't judder either.

 

It is easy to see from the youtube video how the judder can occur.

 

Given a choice I would have the DMF every time . I much prefer the quieter and more relaxed driving experience that the X250 chasis gives over the previous model, even if it does take a little more skill to reverse without juddering.

I remember having a new Marina van which juddered forward and backwards, wouldn't go round bends and needed ear plugs over 50 mph., but it was back to basics and easy to repair! We wouldn't want to go back to those days would we? >:-(

[davenewellhome]

I don't know the answers to all your questions Brian but I'll throw in my two penn'orth for what its worth.

 

A SMF damps out the variations in power and torque delivery from the engine by means of its mass, i.e. its a fairly heavy lump of metal and the lumpier the engine the heavier the flywheel required to damp its delivery variations.

 

A DMF by contrast damps out the same variations by means of a two pieced flywheel assembly connected together via springs which damp out the variations. This allows the Flywheel assembly to be considerably lighter which gives two benefits:

1, lighter overall weight which can contribute to better fuel economy.

2, the lower flywheel mass gives a more responsive engine.

 

The beauty of the SMF is its simplicity, it doesn't really get any simpler than a heavy lump of steel does it? The major downsides of DMFs are:

1, they are prone to breakdown of the springs.

2, because they have a lower overall mass they also have a lower thermal mass, this means the flywheel assembly cannot absorb the heat generated by friction on the clutch plate to the same level as a SMF and will overheat a lot quicker (as evidenced by the number of X250 owners complaining of smoking clutches after very short times).

3, an increase in performance of the engine might well require different springs in the DMF which would realistically mean replacing the DMF completely as it is not normally possible to alter them.

 

Hope this helps, D.

[Rayjsj]

Slim - 2008-10-29 4:22 PM

 

even if it does take a little more skill to reverse without juddering.

>:-(

 

Are you saying that all of the problems with Reversing X250's up an incline

are down to the skill of the driver ??

I think there are a few(more than few) people who would argue that point with you. (you don't work for Fiat do you ??)

Even if you are right, a gearbox shouldn't destroy itself after being asked to propel it's vehicle backwards uphill, should It ?

Over-revving and slipping the clutch WILL destroy the clutch, especially a DMF one. But that does'nt explain the 'porcelain' gearboxes.

I think you are wrong. And Yes, bring back WELL designed, Simplicity to Motoring. :D :D

[Guest JudgeMental]

I always thought they were to reduce vibration....I asked my ford dealer some time ago regards changing and can't remember what he said other then it would make the driving experience worse.

 

Just back from a long weekend in France, and after 18 months of ownership I and still managing to stall it frequently....but its a small price for what is essentially a satisfying vehicle IMO.

[Brian Kirby]

Well, firstly thanks for that brilliant little animation, Neill.  Very slick!

So, it isn't really about fuel economy, but about damping engine vibrations.  I must say I'm tempted to wonder just how harsh our Transit would be with a conventional clutch/flywheel assembly.  You'd need to try both, in the same vehicle, to find out.  Anyone feel like funding some research?

Somehow, the extra responsiveness from the lighter flywheel doesn't seem that critical in a commercial vehicle; in a light car, yes, but in a van?  Besides, a bit more damping of the engine's responses might be useful in curtailing its stall tendency as well.  (Anyone driven a 2CV?  You drive them on the flywheel, rather than the accelerator.  600cc, no torque and no HP, but once you get their dirty great flywheel spinning, you can get wheelspin in second gear no trouble, and scorch off like lightning - for at least 20 yards.  :-))

Would I contemplate changing?  I just might, if it were cheaper than a replacement DMF clutch, especially if that fails in under 45,000 miles.  But will we still have the same van then?  Who knows?

But really, is NVH really all DMFs are about?  It does seem a bit of a retrograde step to install something so apparently fragile and fault prone even if it is quieter.  After all, what do we really want?  Reasonably economical, reliable, vehicles; or just quieter ones?

Out last van was a Fiat 2.8 JTD, and it was noisier that the Transit.  However, it would pull smoothly from tickover, it was a delight to drive in traffic, it pulled away without fuss or drama on wet, icy, muddy, and snowy conditions, and tight manoeuvres did not require a slipping clutch.  The fuel economy wasn't as good as the Transit (25MPG vs 29MPG), but that 2.8 Fiat engine never returned good fuel economy in any of its incarnations.  Not all of that is DMF relevant, but even if it was noisier and thirstier, it was infinitely more controllable when fine control is required.  If I had the choice, I'd settle for a bit more noise in exchange for better slow speed control.

In the meantime, thanks for all your replies.

[sunbeam]

I have fitted more than a dozen solid type clutches in place of the mass type one because they dont give any problems and if anything have a lighter and smoother feel plus the parts are about £250 cheaper, as far as weight is concerned there aint much diffs. (?) (?)

[Guest JudgeMental]

sunbeam - 2008-10-29 7:52 PM

 

I have fitted more than a dozen solid type clutches in place of the mass type one because they dont give any problems and if anything have a lighter and smoother feel plus the parts are about £250 cheaper, as far as weight is concerned there aint much diffs. (?) (?)

 

Does this solve the stall problem with new Transit?

[Slim]

Ravisi

I have to agree with all you say and perhaps I used the term skill when I should have used Perseverance and hoping for level ground to reverse on.

It will also judder starting off forward but a few more revs and power seems to overcome that, but in reverse you don't go as fast, so is reverse gear too high?

I would like a test drive with an X250 with a solid flywheel to see how it performed before I changed.

With DMF it is easier to stall the engine so I was surprised to read that both flywheels weigh about the same.

Off topic a bit, but our X250 is a Peugeot, but the engine is stamped "Ford". Is it really a Transit engine?

I would love to have simple technology that I could service and repair, but I can now cruise fast in quiet comfort compared to 10yrs ago. So for the moment I put up with the quirks.

 

 

[Guest JudgeMental]

Yes the engine's are a shared development.....so many non ford owners can be surprised to open their bonnet to reveal a Ford badged lump....

[rupert123]

So people would like to go back to simple technology, well not me I remember the simple stuff of the 1970's only to well. Points you had to change every few thousand miles, valves burning out, bearings and rings going, decokes, remember them. You were lucky if an engine/gearbox lasted 30,000 miles never mind the 200,000 which is now common place. Sure vehicles have teething problems but they always have. The DMF which some seem to assume is new has been around since 1987 to my knowledge and is better in every way than a solid flywheel, is it to blame for the vibrations in some Fiats, no of course not.

[Derek Uzzell]

I'm reliably informed that Ford offers an 'official' SMF replacement kit for the vast majority of Transit Mk 6/7 variants that start life with a DMF. The notable exception (when I last explored this) was the recently-introduced FWD Mk 7 with 2.2-litre 140PS motor and 6-speed gearbox.

 

Regarding JudgeMental's stalling question, I can't really see why swapping his Transit's DMF for a SMF should improve things. As Sunbeam advises, the parts included in a SMF kit aren't likely to weigh much more than the DMF unit they replace. OK, if the SMF were massively heavier than the original DMF, then it might possibly tame the stalling characteristic, but otherwise not.

 

I'm told that the 2.0litre 125PS TDCi diesel motor in the Mk 6 Transit and the 130PS 2.2litre motor in the Mk 7 are first-cousins and share the same gear ratios. My experience of a 2005 Mk 6 Transit with the former motor suggests that the tendency to stall when moving off is due to a combination of things. These include a lightweight flywheel/clutch assembly, a high 1st-gear ratio, a 'no way back' engine management system that stops the motor stone-dead if the revs drop below tick-over speed, and the manner in which the motor reacts to the throttle pedal. One might have thought that the Mk 7 motor's 200cc increase in capacity would have helped matters, but this seems not to have been the case. I've always felt that Ford shortened even further the accelerator-pedal travel on Mk 7s (which definitely wouldn't assist delicate throttle control) - certainly, when I looked at early FWD versions I thought the all-or-nothing accelerator-pedal movement was atrocious. The only consolation I can offer is that my Mk 6, that was a brute for stalling for a long time, after around 15k miles seems to have become less aggressive. This may be because the motor will have loosened up and/or I'm now especially careful when moving off not to let the revs fall back. Whatever the cause(s), I rarely stall the thing nowadays, though it does need saying that it's definitely not stall-proof and will still do it if I drop my guard.

 

Regarding burning out clutches on X250 Citroen/Fiat/Peugeot-based motorhomes, I believe George Collings comments on page 205 of October 2008's MMM are very relevant.

 

In my Hobby's case, if the motorhome is travelling sufficiently quickly to have the clutch fully engaged in 1st gear and the motor well into its 'power band', then the vehicle can climb (and maintain speed) on very steep inclines. But I'd be very reluctant to attempt a hill-start on such inclines as I know full well it would be placing the clutch under serious stress. Of course things become a whole lot more difficult when reversing, as it's less natural, one hasn't the same field of view and will normally wish to perform any manoeuvre at a much lower speed.

 

I actively try to avoid situations where I might be forced into having to start the Hobby from rest on a steep slope. This is not just because I know there will be a big bill if its DMF gets damaged, I'd do the same if it had a SMF assembly. It's primarily because, due to my Transit's high 1st gear, there's absolutely no way I can get the beggar to move off on a steep hill without slipping the clutch much more than I care to. If anyone wants to suggest that this high bottom-gear makes the chassis 'unfit for purpose' for a 3500kg motorhome conversion, I won't disagree. I don't know what my motorhome's reverse-gear ratio is, but, on the one occasion when I experimented with beginning to reverse up a very steep slope, it certainly felt high and I curtailed the trial immediately.

 

What has perplexed me about the X250 in-reverse juddering business - right from the beginning - is not so much that the problem exists or what's causing it, but that some vehicles are reported as evidencing severe symptoms, while others (with apparently an identical chassis specification) are claimed to show no symptoms whatsoever. This seems very strange for mass production vehicles built using heavily automated methods. One might perhaps expect the juddering characteristic to be present in all identical-spec vehicles to a greater or lesser degree, but not that some judder madly and others don't judder at all.

 

Siffice to say, if you've got an X250-based motorhome and you find that it begins to 'judder' (I don't think the characteristic has ever being adequately described on this forum) when reversing, if you try to counter this by increasing the engine speed and slipping the clutch for any length of time, then the clutch WILL inevitably fail and probably sooner rather than later.

[Brian Kirby]

rupert123 - 2008-10-30 12:31 AM ............... The DMF which some seem to assume is new has been around since 1987 to my knowledge and is better in every way than a solid flywheel, is it to blame for the vibrations in some Fiats, no of course not.

Now Rupert.

My original question was what is the advantage of the DMF?  I asked because it seems to bring problems as well as advantages, and it seems for many of us the problems are apparent, whereas the advantages are not.

Your part quoted response above, if taken as a reply to that original question, falls some way short of an answer.  Granted, it is a strong assertion, but you provide no evidence to support that assertion.

So, can you please quantify exactly how the DMF is "better in every way than a solid flywheel", rather than just asserting that it is?  Then we can have an informed debate, instead of just a disagreement. 

The only good point I've read so far is a reduction in NVH.  What other evidence can you offer in favour of the accused?

[Brian Kirby]

Hello Derek, and thanks for your, as usual, thoughtful response.  You raise a number of interesting points, so to aid reply; I’ve carved up your post a bit.  Apologies for the liberty.

“I'm reliably informed that Ford offers an 'official' SMF replacement kit for the vast majority of Transit Mk 6/7 variants that start life with a DMF.  The notable exception (when I last explored this) was the recently-introduced FWD Mk 7 with 2.2-litre 140PS motor and 6-speed gearbox.”

Interesting.  I hadn’t heard that Ford offer this kit for their own vehicles.

“Regarding JudgeMental's stalling question, I can't really see why swapping his Transit's DMF for a SMF should improve things.  As Sunbeam advises, the parts included in a SMF kit aren't likely to weigh much more than the DMF unit they replace.  OK, if the SMF were massively heavier than the original DMF, then it might possibly tame the stalling characteristic, but otherwise not.”  

Possibly because the lining material in a DMF, if I’ve understood the diagrams right, bears on the flywheel face further towards its periphery.  This would seem to mean the friction material has a greater lever arm against the flywheel as the clutch is engaged, and so a greater capacity to stall the flywheel.  It would also mean the speed of the mating surfaces is higher, and so liable to generate greater friction/heat if slipped to any extent, but also that greater engine power is needed to counter the stall effect, generating a kind of “feed back loop”. 

“I'm told that the 2.0litre 125PS TDCi diesel motor in the Mk 6 Transit and the 130PS 2.2litre motor in the Mk 7 are first-cousins and share the same gear ratios.  My experience of a 2005 Mk 6 Transit with the former motor suggests that the tendency to stall when moving off is due to a combination of things.  These include a lightweight flywheel/clutch assembly, a high 1st-gear ratio, a 'no way back' engine management system that stops the motor stone-dead if the revs drop below tick-over speed, and the manner in which the motor reacts to the throttle pedal.  One might have thought that the Mk 7 motor's 200cc increase in capacity would have helped matters, but this seems not to have been the case.  I've always felt that Ford shortened even further the accelerator-pedal travel on Mk 7s (which definitely wouldn't assist delicate throttle control) - certainly, when I looked at early FWD versions I thought the all-or-nothing accelerator-pedal movement was atrocious.  The only consolation I can offer is that my Mk 6, that was a brute for stalling for a long time, after around 15k miles seems to have become less aggressive.  This may be because the motor will have loosened up and/or I'm now especially careful when moving off not to let the revs fall back.  Whatever the cause(s), I rarely stall the thing nowadays, though it does need saying that it's definitely not stall-proof and will still do it if I drop my guard.”

Hear, hear!  I am finding the same improvement and, with 10,000 now on the clock, things are somewhat better.  Part of this is due to a slight change in technique.  If the engine begins to falter on drive away, instead of prodding the accelerator to increase power, as I usually would, I first momentarily dip the clutch, to remove load, and then titivate the accelerator.  It doesn’t always work, but it helps.

“Regarding burning out clutches on X250 Citroen/Fiat/Peugeot-based motorhomes, I believe George Collings comments on page 205 of October 2008's MMM are very relevant.”  

Agreed, ‘though I think they are equally relevant to other motorhomes.

“In my Hobby's case, if the motorhome is travelling sufficiently quickly to have the clutch fully engaged in 1st gear and the motor well into its 'power band', then the vehicle can climb (and maintain speed) on very steep inclines.  But I'd be very reluctant to attempt a hill-start on such inclines as I know full well it would be placing the clutch under serious stress.  Of course things become a whole lot more difficult when reversing, as it's less natural, one hasn't the same field of view and will normally wish to perform any manoeuvre at a much lower speed.”

 “I actively try to avoid situations where I might be forced into having to start the Hobby from rest on a steep slope.  This is not just because I know there will be a big bill if its DMF gets damaged, I'd do the same if it had a SMF assembly.  It's primarily because, due to my Transit's high 1st gear, there's absolutely no way I can get the beggar to move off on a steep hill without slipping the clutch much more than I care to.  ……………………………………..”

Ours has a bit more weight behind the axle than yours, so less FWD traction.  I just end up using the front tyres as an auxiliary clutch under these conditions (though not in reverse!).  Probably cheaper?

“What has perplexed me about the X250 in-reverse juddering business - right from the beginning - is not so much that the problem exists or what's causing it, but that some vehicles are reported as evidencing severe symptoms, while others (with apparently an identical chassis specification) are claimed to show no symptoms whatsoever.  This seems very strange for mass production vehicles built using heavily automated methods.  One might perhaps expect the juddering characteristic to be present in all identical-spec vehicles to a greater or lesser degree, but not that some judder madly and others don't judder at all.”

I assume, in common with most other manufacturers, the Sevel plant works on a “just in time” basis, with many components delivered form multiple sources.  Whether this extends to DMF assemblies I know not, but if it does, it seems at least possible that one producer’s product is poorly matched to the engine characteristics, or that their quality control is suspect, giving variable results.  It must also be true that even with the precision of robotic production; the tolerances necessary for fit can accumulate across components with adverse, but fairly random, consequences.

“Suffice to say, if you've got an X250-based motorhome and you find that it begins to 'judder' (I don't think the characteristic has ever being adequately described on this forum) when reversing, if you try to counter this by increasing the engine speed and slipping the clutch for any length of time, then the clutch WILL inevitably fail and probably sooner rather than later.”

Amen!

[Slim]

Excellent posts from all concerned, and back to the original question of the advantages / disadvantages of a DMF. My new Focus I believe has a DMF, but my previous one didn't. The new one will pull at far lower revs with no vibration at all

Is this therefore a plus or a minus point as I assume the DMF is damping the engine vibrations - GOOD, but at the same time stressing the springs inside - BAD. I think you must make your own choice.

Having gleaned more information from this thread, I suspect that the right gear at the right time would help conserve this seemingly delicate part of the drive train.

Oh and Yes, I would still like to keep my DMF with the more refined and comfortable driving environment please.