I thought flywheel is a component of all transmissions but web searches suggested that automatics often use flex-plate. I was not aware of this term before!
So does it mean that all autos (especially those with fluid coupling) use flexplate instead of DMF?
I have heard about lots of horror stories on DMFs failing - so are these confined to diesel manuals only?
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DMF is used to damp vibrations in the engine as the drive is taken up. Used to be done with springs in the clutch driven plate, but DMFs can accommodate more. Not necessary on an auto as the torque converter smooths things out. Flex plate has been std way of transferring the drive from the crank to the TC input for a long time.
That's not to say of course that some autos are not fitted with DMFs. However, the main cause of them failing - driver abuse - is removed.
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What counts as 'abuse' in the context of a DMF?
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Excessive clutch slip, eg holding it on the clutch on hills, or using too much revs pulling away. Although I have no evidence, overheating the DMF seems to be contributory factor.
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>> Excessive clutch slip, eg holding it on the clutch on hills, or using too much
>> revs pulling away. Although I have no evidence, overheating the DMF seems to be contributory
>> factor.
Excess heat is a big problem for DMFs as it weakens the rubber cushions between the two parts of the unit and allows excess movement, reducing vibration damping, and sometimes causing a lot of noise as the movement between the two masses becomes less controlled. In extreme cases, the two parts of the flywheel can seize together, as ours did on our old mk4 Golf TDI. This throws the balance out and makes for very harsh progress indeed. Can also make it a pig to get to the bolts to remove the flywheel.
Excessive clutch slip should be avoided on any DMF equipped car, and a clutch slipping through wear should be replaced immediately to avoid having to replace the flywheel as a matter of course.
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Rough gearchanges can impact on it as well but slipping clutch (heat) is the biggest thing to avoid. Surprising the number of people who do it, I would never buy a second-hand DMF vehicle. As that rules out diesels, then that is no hardship for me.
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I belive that some petrol powered cars have DMFs.
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>> I belive that some petrol powered cars have DMFs.
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Yes, quite a few nowadays.
DMFs tend not to give as much grief stuck on the end of a petrol engine, as they generally run smoother and with less vibration than equivalent diesels, so the flywheel gets an easier time.
My Golf GTI 1.8T was on 147k on its original clutch and DMF. While the clutch was showing signs of coming toward the end of its life, biting right at the top of a very heavy pedal, there was nothing to indicate any issue with the DMF at all. I sold it on before it got worse, so I can't say, but most people convert these to solid flywheel anyway if there's any doubt. There are kits from reputable manufacturers to do this, which have very good feedback.
Last edited by: DP on Mon 7 Sep 15 at 22:52
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Putting torque through it at the wrong engine speed is probably the quickest way to see it off. The engine management computer should be aware of this though and limit the torque available (one of the reasons I ditched the Insignia, because the ECU made it impossible to accelerate from idle speed in third gear).
You can get torque converters with a dual-mass flywheel and it's probably essential in a diesel auto given you can get a lockup in every gear.
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Talking of autos, Fursty, you've not mentioned your new Volvo much, which may or may not be a good thing. How do you find the adaptive cruise now you have it? Up to snuff or not as useful as you hoped?
Doesn't need to be a new thread I don't think.
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Which autos have a TC and a DMF? I have not heard of one. I thought the TC lockup was controlled by the transmission ECU and only occurred when the TC turbines were speed matched.
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Generally it's only the high performance petrol engines that have DMF although they are appearing in some versions of three-cylinder affairs. Neither of which appeal to me.
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Do autos have DMF? - RichardW
