Dual or single mass flywheel?
Discussion
Few points:
DMFs have gotten better. A good quality replacement might last significantly longer than the original. With that in mind, is the car likely to need another during it's life? During your ownership? If the answer is 'no', fit a new DMF in my opinion. Don't chose it as a cost saving option because the price difference between DMF and SMF pales into insignificance in comparison to the cost of the labour to fit it. Regardless of what SMF suppliers might tell you, an SMF cannot do the same job as a DMF.
Remember to ensure the space cylinder/release bearing is replaced.
DMFs have gotten better. A good quality replacement might last significantly longer than the original. With that in mind, is the car likely to need another during it's life? During your ownership? If the answer is 'no', fit a new DMF in my opinion. Don't chose it as a cost saving option because the price difference between DMF and SMF pales into insignificance in comparison to the cost of the labour to fit it. Regardless of what SMF suppliers might tell you, an SMF cannot do the same job as a DMF.
Remember to ensure the space cylinder/release bearing is replaced.
There has been many PH topics on DMF`s with endless discussion on the pro`s and con`s.I`m old school and to me a flywheel was just a lump of metal that stayed on an engine for all its life.When DMF`s arrived (and the problems started)I thought what`s the point? I then contemplated fitting the "solid kits" until I read various reports on crankshaft failures,bell housing cracks etc.
As said above these new generation engines are designed around a DMF.My advice is replace the DMF with a top quality O/E part and do not be tempted to get cheep stuff online or solid kits.
As said above these new generation engines are designed around a DMF.My advice is replace the DMF with a top quality O/E part and do not be tempted to get cheep stuff online or solid kits.
A farm mechanic form our local was discussing DMFs after replacing the one in his van and mentioned that some machines he repairs have a dual mass drive coupling fitted to later models on the input shaft to minimise`take up snatch,just a straight two foot long solid shaft with splined ends.
These couplings apparently fail rapidly and a solid(older/original design)coupling is now the only replacement.
This he assured me would always result in the input shaft shattering after around 160 running hours.
He also assured me that the earlier model with the solid coupling fitted form new never failed.
His theory is that the dual mass coupling causes vibration during use which weakens the shaft and the solid replacement not supplying the cushioning affect of a DMF finishes it off.
Backed up by the fact that that the original solid coupling model never broke a shaft and that only when the solid replacements were fitted that the failure would occur.
Inspecting broken shafts he noticed they all snapped where small,obviously older cracks joined to make one big radial break in the opposite direction to power application.
Not a theory I have ever heard mentioned before concerning DMFs but as the same principals of operation apply,plus a crankshaft has what is essentially some big weights swinging from it.
Add to that the fact that most will continue to drive them until they are shaking like a s
tting dog and I suppose looking at it that way it could be possible that the DMF could be cause of failure in the first place.
These couplings apparently fail rapidly and a solid(older/original design)coupling is now the only replacement.
This he assured me would always result in the input shaft shattering after around 160 running hours.
He also assured me that the earlier model with the solid coupling fitted form new never failed.
His theory is that the dual mass coupling causes vibration during use which weakens the shaft and the solid replacement not supplying the cushioning affect of a DMF finishes it off.
Backed up by the fact that that the original solid coupling model never broke a shaft and that only when the solid replacements were fitted that the failure would occur.
Inspecting broken shafts he noticed they all snapped where small,obviously older cracks joined to make one big radial break in the opposite direction to power application.
Not a theory I have ever heard mentioned before concerning DMFs but as the same principals of operation apply,plus a crankshaft has what is essentially some big weights swinging from it.
Add to that the fact that most will continue to drive them until they are shaking like a s
tting dog and I suppose looking at it that way it could be possible that the DMF could be cause of failure in the first place.shoehorn said:
A farm mechanic form our local was discussing DMFs after replacing the one in his van and mentioned that some machines he repairs have a dual mass drive coupling fitted to later models on the input shaft to minimise`take up snatch,just a straight two foot long solid shaft with splined ends.
If this is a tractor PTO (power Take Off) coupling it's probably to reduce the torsional vibration caused by the universal joints in the PTO shaft, which can run at unequal angles in some cases. A DMF would not be required to reduce snatch, you would simply need a sprung drive, like the center of the clutch friction plate.shoehorn said:
His theory is that the dual mass coupling causes vibration during use which weakens the shaft and the solid replacement not supplying the cushioning affect of a DMF finishes it off.
Far more likely that the shafts on the older machines without the DMF are tougher than the ones used with the DMF, since they would have to cope with the higher torque peaks, and the torsional vibration that induces fatigue.Mr2Mike said:
Far more likely that the shafts on the older machines without the DMF are tougher than the ones used with the DMF, since they would have to cope with the higher torque peaks, and the torsional vibration that induces fatigue.
These machines are self propelled(mitsubishi diesels,so no pto shaft mis-alignment is possible)and as I understand it the coupling is engaged by sliding another shaft up to meet it, where a reverse arrangement to a starter handle is used,the drive or speed of the motor keeps it engaged rather than to throw it out like a starter handle,there is no clutch or sprung mechanism.The dual mass affair was fitted to the supply side of the coupling and allowed about 100-120 degrees of twist to take up drive,then it was supposed to return to it`s at rest position to maintain joint alignment and balance once the initial drag was overcome.
The earliest of these machines had a crude 3 cylinder engine fitted that run at high rpm to produce the power needed,but these would cause vibrational wear and thow off belts but apparently never broke a shaft in operation,the same shaft has been used throughout the range only the couplings have been altered.
We asked all these and many more questions about this.
Today I showed this thread to a retired major of the royal engineers(bridge specialist)taking into consideration his knowledge of metals and the effects of stress/torque/vibration and any other force acting upon them,plus his understanding of physics and general engineering practice.
He spent a while explaining how different frequencies of vibration affect metals and so on.
He talked about how the crank,rods,flywheels etc. are all balanced to ensure smooth running and durability and the notion of fitting something that will upset that balance,a faulty dual mass fly wheel on one end of that shaft would alter the structure of the metal grain over time due to vibrations etc.
With a faulty dmf the frequency of vibrations will alter the metal over time slowly,moving the grain of the metal the same as when working it,if is changed by then fitting a solid mass the change in frequency occurs too quickly,the grain tears rather than moving together slowly over time and then a break occurs.
Much like a spring,it will compress over and over but one day it will snap,and the break will be one made of hundreds of little cracks.
He finished by saying in his words,It would be like hitting a piece of metal hundreds of times with little tiny hammers and never having any visual effect,you could go on hitting forever.
Fitting a solid flywheel is akin to then coming along with a sledge hammer and hitting the same piece of metal once,breaking it and proclaiming the sledge hammer did all the work.
It may be true but if you don`t know what damage the small hammers did in the first place you can never be sure of the sledgehammers triumph.
What he was saying basically is that if you cant prove why it broke then any sound theory is plausible,until dis-proven by comparative testing.
He agreed that without that you would never know but did agree that the farm mechanics assessment was sound and plausible.
My DMF failed on a Mondeo TDCI after 85k didn't help that the previous owner had previously just replaced the clutch plate, after several startermotor rebuilds I had no option but to replace, I got a fair deal on a new DMF fitted and thought I would change like for like as the next DMF change would be at or around 170k that'll do for now and if I sell I can prove a full DMF replacement
Driving with mechanical sympathy would mean slipping the clutch, driving gently, being hyper aware all the time.
Rather ruins the driving experience for the sake of a few hundred quid
By a cheaper car with a standard flywheel don't bodge what manufacturers have spend millions developing and I can assure you if they could get away with fitting a cheaper system they would.
A mate of mine some years back was developing a software traction control to replace fords throttle cable control, this saved 15 dollars per car, sell a million cars well you work out the math
Rather ruins the driving experience for the sake of a few hundred quid
By a cheaper car with a standard flywheel don't bodge what manufacturers have spend millions developing and I can assure you if they could get away with fitting a cheaper system they would.
A mate of mine some years back was developing a software traction control to replace fords throttle cable control, this saved 15 dollars per car, sell a million cars well you work out the math
Hi Phil
I have a 54 plate Mondeo 130TDCI thats now reading 147,000 miles on its original DMF and is still ok, when looking into a replacement i was advised to replace like for like as the original one has been no trouble! Hope you find a suitable salution with yours..
PS hows the white beast progressing?
Martin
I have a 54 plate Mondeo 130TDCI thats now reading 147,000 miles on its original DMF and is still ok, when looking into a replacement i was advised to replace like for like as the original one has been no trouble! Hope you find a suitable salution with yours..
PS hows the white beast progressing?
Martin
I'm not sure which brands are good now but when I had my Mondeo TDCI it was LUK or Sachs. I know I've said it before but have the concentric slave replaced and also the starter motor inspected at the same time.
Regarding the idea of 'preserving the DMF by driving with mechanical sympathy'- mechanical sympathy will only go so far. The DMF is working hardest at or near engine idle speed because every two revolutions of the crankshaft the four combustion strokes each produce a massive torque spike at a frequency which is quite low compared to at higher engine speeds. The best thing you can do is drive the car keeping the engine revvs well above idle speed. Smooth gear changes and revv-matching are unlikely to make a significant difference to the life span of the flywheel.
Regarding the idea of 'preserving the DMF by driving with mechanical sympathy'- mechanical sympathy will only go so far. The DMF is working hardest at or near engine idle speed because every two revolutions of the crankshaft the four combustion strokes each produce a massive torque spike at a frequency which is quite low compared to at higher engine speeds. The best thing you can do is drive the car keeping the engine revvs well above idle speed. Smooth gear changes and revv-matching are unlikely to make a significant difference to the life span of the flywheel.
Thanks for all your replies and advice. I've bought another dual mass flywheel, clutch and slave cylinder and will be having them fitted soon. Incidentally, I got the bits from euro car parts - they,ve got a 15% off offer online on clutches and flywheels at the moment, which is a bonus! Cheers all.
I am new to the forum but not new to the world of automotive engineering. I have worked up to the level of RND, design & manufacturing and automotive electronics & software. The point I am making, if an engine is designed, manufactured and tested with a dual mass flywheel, you should NEVER use a single mass flywheel as a replacement. I could go into the mathematics side of things and bore you to death so just take my word for it.
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