Dual Mass Flywheels - Your views?

[Volvo2002]

As someone who is relatively new to the inner workings of cars and have recently taking an interest thanks to my clutch symptoms, I wondered what some of the more experienced users have to say regarding DMFs (Dual mass flywheels)?

From what I gather this was a solution to a problem that didn't exist or didn't need fixed. From my own findings the benefits are as follows...

To eliminate excessive transmission gear rattle, making driving comfortable at any speed,
reduce gear change/shift effort, and
increase fuel economy.

From speaking with two different mechanics who have experience with both a single and dual mass flywheel, their own conclusion was that the DMF really doesn't offer much of a difference in the feel of the car when it's being driven. Of course that is just their opinion and I wanted to know other peoples views on this?

My own car a 52 REG Volvo S40 1.8 petrol has a DMF and my worry is the pedal pulsation/judder/pedal weight changes is linked to a bad DMF. Also the failure of a DMF seems common in diesel motors.

Anyway I'm new to all of this and would be interested to hear some of your thoughts

[popuptoaster]

A pointless waste of money when it eventually goes wrong, which it will.

great idea by manufacturers,

"Lets replace something which never breaks with something that will fail AND is expensive AND difficult to get out"


Its bollocks about smoothness and easier gear changes anyway, anyone who cares about that buys an automatic and if you want better mpg stop fitting wide low profile tyres on the cars is what I reckon.

[tt82]

Whilst looking into the problems with my brothers audi 1.9 diesel engine it appears that they suffer with DMF's and most revert back to a solid.

[Daim]

A DMF is something, which will not really improve to much, other than comfort.

The problem being the following:

A 4 cylinder engine doesn't run totally smooth. So it means a powerstroke doesn't straight away get followed by another one somewhere in the drive engine (a 6 cylinder does). So it will always be accelerating and decelerating.

So, a car with 4 cylinders and a SMF will, if you leave it running at idle but in gear (all cars can do this), judder slightly, as the engine doesn't transfer a constant power to the gear box.

In order to remove this (yes, people would complain about this, even in the old 700 and 900 series), the car and gearbox manufacturers came up with the DMF. This has enough "spring rate" inside to smoothen out the engine.

The older 700 and 900 series had a little something behind the gearbox and infront of the prop - it is a little rubber disc with 6 screw holes. 3 for each side (prop and gear box). This acts as a damper between engine and drive wheels. It is constantly stretched and compressed whilst driving - no matter at what RPM.

As a FWD car or rear engined car doesn't have enough space to fit some rubber dampers, the DMF was introduced.

It reduces stress on the gearbox as well as drive shafts etc. and produces more comfort.

So it isn't a "solution to a problem which doesn't exist". It is a solution to a problem to a long time issue which got more and more common as FWD and 4 (and 5) cylinder engines were getting more and more common.

[owyn]

I thought it was introduced thanks to modern diesels having such a choppy torque profile across the power stroke.

With the higher injection pressures and direct injection in modern diesels you get a great big power spike early in the expansion stroke, the DMF tries to smooth this out.
Unfortunately adding more moving parts tends to make things less reliable.

[Volvo2002]

Originally Posted by owyn

I thought it was introduced thanks to modern diesels having such a choppy torque profile across the power stroke.

With the higher injection pressures and direct injection in modern diesels you get a great big power spike early in the expansion stroke, the DMF tries to smooth this out.
Unfortunately adding more moving parts tends to make things less reliable.

More moving parts = reliability compromise!

Such a good idea, shame about the execution.

[Volvo2002]

Originally Posted by Daim

A DMF is something, which will not really improve to much, other than comfort.

The problem being the following:

A 4 cylinder engine doesn't run totally smooth. So it means a powerstroke doesn't straight away get followed by another one somewhere in the drive engine (a 6 cylinder does). So it will always be accelerating and decelerating.

So, a car with 4 cylinders and a SMF will, if you leave it running at idle but in gear (all cars can do this), judder slightly, as the engine doesn't transfer a constant power to the gear box.

In order to remove this (yes, people would complain about this, even in the old 700 and 900 series), the car and gearbox manufacturers came up with the DMF. This has enough "spring rate" inside to smoothen out the engine.

The older 700 and 900 series had a little something behind the gearbox and infront of the prop - it is a little rubber disc with 6 screw holes. 3 for each side (prop and gear box). This acts as a damper between engine and drive wheels. It is constantly stretched and compressed whilst driving - no matter at what RPM.

As a FWD car or rear engined car doesn't have enough space to fit some rubber dampers, the DMF was introduced.

It reduces stress on the gearbox as well as drive shafts etc. and produces more comfort.

So it isn't a "solution to a problem which doesn't exist". It is a solution to a problem to a long time issue which got more and more common as FWD and 4 (and 5) cylinder engines were getting more and more common.

So, a car with 4 cylinders and a SMF will, if you leave it running at idle but in gear (all cars can do this), judder slightly, as the engine doesn't transfer a constant power to the gear box.

Interesting never knew that. Thanks for the informative post Daim

[Volvo2002]

Originally Posted by tt82

Whilst looking into the problems with my brothers audi 1.9 diesel engine it appears that they suffer with DMF's and most revert back to a solid.

Seems common with Ford transit vans being converted from DM to SM.

This is not an option for every car as it seems some are designed around the DMF and it's not wise to convert back to a SMF.

[volvorocks]

After reading up on DMF they appear to be for less noise vibration and harshness, better fuel consumption,for less stress on the gearbox/ transmission from high torque output engines.It appears they are more or less being seen in some instances as a 'consumable' like brake pads are..!!!

Apparently Ford and Mazda are looking at fitting some electronic trickery to limit torque output in first and second gear instead of using DMF.

Thoroughly enjoyable research - off for a kip....

Regards

[Daim]

Originally Posted by volvorocks

After reading up on DMF they appear to be for less noise vibration and harshness, better fuel consumption,for less stress on the gearbox/ transmission from high torque output engines.It appears they are more or less being seen in some instances as a 'consumable' like brake pads are..!!!

Apparently Ford and Mazda are looking at fitting some electronic trickery to limit torque output in first and second gear instead of using DMF.

Thoroughly enjoyable research - off for a kip....

Regards

Volvo has that already. The T5 in the P1 does that in first. It won't put full power on the gearbox in 1st. Volvo also has had a "power reduction" on the autoboxes for yonks. The old 960 with the AW30-43LE had that (the gearbox would wait for a signal from the engine saying that it has reduced engine output in order to get a smooth gear change).

Years ago you could get the over these DMFs by having clutch plate springs. But as the engines got more and more powerful (say 70 hp/liter of displacement instead of 30 hp like in the day), the forces got higher and the work on the clutch would simply kill it quicker than you think.