Dual Mass Flywheels - Your views?

[Bill_56]

My own understanding is as follows...

It's worth remembering that the DMF is working all the time, not just when you let the clutch out.

It's purpose, as has been said, is to smooth out the torque pulses that would otherwise lead to unpleasant cabin vibration and/or premature transmission wear & tear. These pulses are of course per-cylinder, per ignition, pulses, not so much to do with clutch activity.

When the engine is running at higher rpm, the torque pulses are closer together, hence don't need so much smoothing. Also, the higher the car's gearing, the more 'resistance' there will be to these pulses, as torque reaction at the crankshaft is proportional to overall gearing, and more resistance means more work for the DMF.

These factors (low rpm and high gearing) conspire to create a much harsher environment for DMFs in a diesel car. DMF's are fitted to many petrol cars too, don't seem to be associated with such common failure.

[Shadeyman]

Originally Posted by Bill_56

DMF's are fitted to many petrol cars too, don't seem to be associated with such common failure.

Petrol engines don't produce huge torque spikes, relatively small compared to diesels, hence they're failure rate is less.

[Volvo2002]

Not DMF related (clutch)

Someone for no apparent reason decides to toast an Audi A5s clutch!!

http://www.youtube.com/watch?v=qQgLJ...eature=related

[Daim]

Originally Posted by Bill_56

My own understanding is as follows...

It's worth remembering that the DMF is working all the time, not just when you let the clutch out.

It's purpose, as has been said, is to smooth out the torque pulses that would otherwise lead to unpleasant cabin vibration and/or premature transmission wear & tear. These pulses are of course per-cylinder, per ignition, pulses, not so much to do with clutch activity.

When the engine is running at higher rpm, the torque pulses are closer together, hence don't need so much smoothing. Also, the higher the car's gearing, the more 'resistance' there will be to these pulses, as torque reaction at the crankshaft is proportional to overall gearing, and more resistance means more work for the DMF.

These factors (low rpm and high gearing) conspire to create a much harsher environment for DMFs in a diesel car. DMF's are fitted to many petrol cars too, don't seem to be associated with such common failure.

If I bring in my car's engine (a typcial NA petrol) in comparisson to the equal sized diesel, you'll probably see it:

2.0l non turbo petrol with 185 nm (no idea what that is in lbft) at 4500 rpm.
2.0l turbo diesel with 320 nm (no idea what that is in lbft but a lot more) at 2000 rpm.

The diesel has all it's torque basically from idle. The petrol will build up it's power (and torque) over a long period. So a constant power increase compared to instant power... Therefore a DMF will hold longer (if you use THE SAME type) in an NA petrol than a turbo diesel. A turbo petrol though can have the same problems...

[popuptoaster]

I'd rather go back to an internal balance shaft in the engine and a normal flywheel, both of which normally last the life of the engine. DMFs are a common failiure point on all types of cars and vans.

Ask any decent sized garage how many they change on modern cars compared to SMF they ever did on older cars.

[Bill_56]

Originally Posted by Shadeyman

Petrol engines don't produce huge torque spikes, relatively small compared to diesels, hence they're failure rate is less.

Agreed,

And moreover, even if a highly tuned petrol engine produced the same or greater torque than a diesel equivalent, the DMF will still be better off, thanks to the higher frequency (higher rpm) of the torque pulses/spikes.

[Daim]

Originally Posted by popuptoaster

I'd rather go back to an internal balance shaft in the engine and a normal flywheel, both of which normally last the life of the engine. DMFs are a common failiure point on all types of cars and vans.

Ask any decent sized garage how many they change on modern cars compared to SMF they ever did on older cars.

Only thing is, internal balace shafts DON'T interfere with the torque peaks. They just counterbalance the engine movements but not the torque... So that wouldn't work what so ever... A 2.3l Ford Duratec has an internal balance shaft. The engine though still has a DMF.

[Volvo2002]

Some excellent posts guys. I'm being educated and fascinated from all of these replies

[Shadeyman]

There are alternatives to DMF's.

A solid flywheel with uprated torsional damping in the clutch plate.....just like it used to be years ago.

I'm not able to find any right now to link to but they are available and work quite well but I'd still prefer a DMF.


Edit.
Here, unfortunately they don't do Volvo.
http://www.prospectautospares.co.uk/...kits_623_1.htm

[Volvo2002]

Originally Posted by Shadeyman

There are alternatives to DMF's.

A solid flywheel with uprated torsional damping in the clutch plate.....just like it used to be years ago.

I'm not able to find any right now to link to but they are available and work quite well but I'd still prefer a DMF.


Edit.
Here, unfortunately they don't do Volvo.
http://www.prospectautospares.co.uk/...kits_623_1.htm

Looked at that site yesterday, yep no Volvos. My problem is probably not flywheel related, I hope!