Many threads here about the fragility and the cost of dual mass flywheels, which i confess i didn't know anything about till probably 12 months ago, thanks to the good chaps here.
I always where poss have proper auto's so haven't wrecked one yet.
There's advice to start the vehicle rolling on tickover and then to make the smoothest of changes, which is admirable, but i for one would be bored to death in minutes, and large cities would grind to a halt, and i'm sure that 99% of drivers would be the same.
Do the likes of the Ford transit and its peers have DMF's?
If they do, how come they aren't falling apart all over the place with disgruntled owners jumping up and down and shouting from the rooftops.
I drove transits back in the 70's, they used the V4 petrol which in its high compression form in the Ford cars would blow a head gasket very often, but in LC form as fitted to transit would last years.
Do they use vastly modified drive trains compared to cars?
I thrashed the living daylights out of them, and the current transit and other similar vans are driven with equal cruelty by their current young drivers.
Have you ever tried to beat a diesel MB sprinter off the lights, they could give a motorcycle a run for its money, so how come these vehicles which are usually driven absolutely flat out survive.
Whats the difference then, and if they don't have the dreaded DMF, how come they don't shake the engine to bits, as apparently a car diesel engine would?
Several times, people have been advised against fitting a modified normal solid type flywheel.
Please don't tell me it comes down to the strength of the gearbox or something, as i understand that vehicles like the hilux and other pick ups, 4 x 4s etc have these dratted things and the hilux box is far from weak.
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The Transit / DMF story has been on here many times - there is a solid flywheel available for the transit, as the DMF was failing too regularly on Transits.
Although I have heard many technical reasons not too swap to a solid flywheel, I have not yet read of anyone having major problems after doing so - but that doesn't mean that this is a problem free solution.
Ford mechanic also told me that "play" in the Transit DMF can give misleading readings from the Crankshaft timing sensor leading to cutting out and other problems.
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"Do the likes of the Ford transit and its peers have DMF's?"
Yes
"If they do, how come they aren't falling apart all over the place"
They are. Starter motor failure is also a problem with them. Metal dust from DMFs gets attracted to magnets on the starter causing it to stick and jam. New starter and new DMF required.
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DMFs aren't fitted to protect any mechanical component, rather, they're fitted to reduce noise and vibration for the driver.
My concern about replacing a DMF with a solid flywheel is centred on the torsional vibration of the crankshaft.
On the crankshaft nose, there's usually some kind of tuned absorber, where the inner of the pully is joined to the outer using a rubber spring. The rubber spring, and the outer pulley mass together are tuned to absorb trosional vibration at a previously calculated frequency, which corresponds to a resonant frequency of the *whole* pulley, crankshaft, flywheel system. Changing the flywheel could knock the pulley/absorber out of tune, putting the crankshaft at risk from failure from torsional fatigue.
If the solid flywheel is designed by the OEM (and might also be supplied as a kit with a modified pulley/absorber) then there won't be a problem, and all you'll notice is more NVH. If, however, the flywheel has been designed by a man in a shed (or any typical tuning comapany), then there's no way to be sure that torsional stress and vibration has been considered properly.
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"Changing the flywheel could knock the pulley/absorber out of tune, putting the crankshaft at risk from failure from torsional fatigue."
If the DMF fails(or partially fails) or a replacement DMF is not properly aligned then I would assume that the Torsional Fatigue of the crankshaft is still at risk.
As a Chemist I have doubts about how rubber can be connected to metal and expected to withstand the changes in temperature and endure daily high Torque / Stress over several years without failing. I assume it should be possible to achieve the same effect without using rubber.
Surprisingly Ford have kept the DMF in most models of the New Mondeo - I would be very interested to know if they changed the design.
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>>I would assume that the Torsional Fatigue of the crankshaft is still at risk.
Once you look downstream of the compliant part of a DMF, then the rubber, the springs, and second mass of the dual mass flywheel and the remainder of the driveline is, largely, decoupled from the pulley, crank, flywheel system.
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A DMF does reduce vibration and harshness in saloon cars (mine), though, given this, I do wonder why they need to be fitted to vans in the light of them being so costly to replace. My car has done 8 years and 70k+ miles on its original DMF (tho' new clutch has been fitted!) so their poor reputation is not common across all types.
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Thankyou for the interesting replies so far gentlemen.
Seems i was completely wrong about the vans being trouble free on this then.
Surprised that the makers fitted the things, surely they could use some normal white van men for testing.
I've never had to replace a normal flywheel, a few starter rings, yes.
R40, it seems you have got away with replacing the clutch without the DMF, which is often advised against on this forum.
Did you change the clutch immediately you became aware of slippage?
I ask as i wonder if you'd allowed it to slip constantly until virtually undriveable, which many would have done, whether the heat generated by the slippage would have caused the DMF to be destroyed too.
Over the years i've got away very cheaply by doing just that, at the first sense of slippage, having just the driven plate relined by a very useful place in Northampton (they would also reline your brake shoes, ideal for unusual vehicles).
Never failed to get 2 driven plates use out of a decent clutch assembly.
Unfortunately, those very handy chaps are no longer there, but then aprts like clutches are much cheaper relatively now, its the DMF that stings.
Would you tell us which car you refer to, i think we'd all like as much experience of this problem as possible.
Is the DMF getting blamed and replaced sometimes when the problem is maybe a nasty clutch plate, i should imagine main dealers would want to change the DMF at clutch renewal to be on the safe side anyway.
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Ok, DMF diesels are problematic - there seems to be substantial evidence for that.
But is it an development & design problem - (ie all DMF diesels are flawed) or poor manufacturing?
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