Should you switch from a DMF to solid flywheel?

"DMF vs SMF which one is right for you?"

flywheel2

Which one is better to have?

Why do manufactures install expensive and potentially unreliable dual mass Flywheels in cars?

What are DMF flywheels and why do people change them for solid ones?

The flywheel in a car helps to store the rotational energy from the engine.

It helps avoid stalling and bogging down and makes it a lot easier to keep a car engine at constant RPM.

So what does a flywheel do?

Well without a flywheel every fluctuation from the engine would be instantly felt along with every slight blip on the throttle.

flywheel4

What then is a DMF?

Firstly a DMF flywheel or more correctly a dual mass flywheel has two sections which are sprung together. The inner one connects to the engine and the outer one connects to the inner one by means of a flexible sprung connection allowing it to move slightly independently of the inner flywheel.

If there is a power blip or 'burp' from the engine the inner flywheel feels this directly but the outer flywheel can move independently to the inner one (within limited confines) and helps to smooth out these little blips.

We find it hard to justify switching from a DMF to an SMF because of the additional risks and the lack of noticeable performance benefits.

Benefits of Dual mass flywheels.

The big benefit of a DMF is that the engine feels silky smooth. All the power fluctuations are smoothed out or dampened down lessening the wear and tear on the transmission and clutch.

Most manufacturers recommend changing the DMF at the same time as the clutch.

Since clutch replacement usually requires removal of the flywheel it makes sense to do both at the same time. DMF are subject to wear and if the sprung link goes will seriously hamper the smooth running nature of the engine.

Benefits of solid flywheels (single mass)

They do not wear out, and as such will not need to be replaced or repaired. They are also cheaper to buy.

They do not break up when they fail. They are more suited to conditions where frequent engine speed changes and gear changes are made.

flywheels

Benefits of DMF

They smooth out the engine causing it to feel silky smooth and this reduces wear on other parts of the transmission.

They are a relatively new innovation but increasing numbers of manufacturers are fitting them to their cars. In a diesel engine a flywheel is an essential item, as few are refined and smooth in operation.

Whereas in smooth petrol engines they are nice to have and noticeable by their absence on some setups, notable some V5's or inline 4 and 3 cylinder engines.

A DMF will also protect an engine as well as the gearbox from shock and vibration.

Should you replace a DMF with a solid flywheel?

It is our considered opinion that unless a car is used extensively for competition or off road you should stick with a DMF.

The additional torque caused by tuning an engine or heavy competition use can quickly destroy a DMF, without which these issues are passed on to the gearbox and drivetrain.

The solution would be to fit a stronger, higher performance DMF but the aftermarket industry seems geared up to offer a lighter solid one as the upgrade option.

A solid flywheel replacement is often regretted by its owner. They cite vibrations and noise as two of the main issues arising from them. Gear changes appear to be required more frequently.

It is tempting to fit a lighter flywheel for performance reasons.

A full discussion of the merits of lighter flywheels can be found here, but, unless you have a serious need for a solid flywheel, TorqueCars recommends you stick with an OEM spec DMF one.

If you have a 6 cylinder engine that is particularly smooth then a DMF seems to be a luxury you can safely drop.

flywheel3

There are plenty of reports out there of drivers and our members who have happily replaced a DMF with a solid flywheel.

They will generally concede that there is no advantage to having a solid flywheel though in terms of performance, so the only consideration is cost.

You should also bear in mind the possible future cost of transmission failure as a result of the additional vibrations.

If you do fit a solid flywheel you can help reduce some of the vibrations by fitting a carbon fiber drive shaft.

Carbon fiber rotationally flexes absorbing some of the torque and shock from engine speed changes and will help dampen things down a little.

People think lighter flywheels are always better than heavy ones, in reality, this depends very much on the use and conditions the car will be asked to perform in.

Both have advantages and disadvantages. We find it hard to justify switching from a DMF to an SMF because of the additional risks of complications and the lack of a performance benefit other than the obvious lower cost.

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9 Responses to “DMF vs solid flywheel conversions”

  1. Ben says:

    I replaced my dual mass flywheel on a d40 nissan navara diesel. It is now harder to keep a constant 100kmh speed, but gear changes are far easier – making it car like to drive rather than truck like with dmf. I have been told the single flywheel runs cooler also, lengthening the clutch life

  2. Chuko says:

    I am a taxi driver and considering converting from DMF to Solid Flywheel on a volvo v40 2002 estate car due to excessive gear changing. Would it be advisable to do so or not?

  3. TCJBOLDIE says:

    IF a DMF is replaced by a solid flywheel then there should be no change in the number of gear changes. Where are reports of damaged transmissions supposedly damaged by solid flywheels as I have had many cars over a 60 year driving history and can’t recall having to repair a damaged gearbox

  4. TCJBOLDIE says:

    Forgot to say if the replacement solid flywheel is the same weight as the DMF one it is replacing

  5. TCJBOLDIE says:

    I would tend to think that if the weights were the same then the need to change gears would be the same regardless of the type of flywheel type.

  6. Leonard yardley says:

    Great read, but is there any difference in slave cylinder life if using a concentric clutch.

  7. Brett says:

    I’ve just replaced my clutch and fly wheel with a single mass and heavy duty clutch, to say the least i am hacked off, my car has gone from silky smooth to feeling like a Mack truck, loud, vibrations, feels like rubbish…don’t do it, stick with duel mass, also now it jumps out of 5th gear, mechanic says my gearbox is worn, and needs a rebuild, only done 172000k,not happy

  8. J du toit says:

    Replaced a dmf with a solid flywheel on a 5 cylinder merc 2,9 diesel motor. Flywheel bolts keep on breaking off within 200 km. Three times. Any advise welcome. Mechanic blames gearbox.

  9. TCJBOLDIE says:

    Replace the Flywheel bolts with ARP’s

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