Why are dmf so expensive?
By Jenni Wirtz | 21 February, 2020
For more than 100 years, Borg & Beck has been a byword for premium products, which is why brand owner First Line Ltd, continues to invest and update its quality control and test equipment in its bespoke technical centre, enabling it to supply products in which technicians can truly rely.
As a result of the company’s investment in its facilities and engineers, Borg & Beck has the knowledge and ability to take its clutch specialism to a new level as it has, for example, adapted the driven plate equipment to be able to test dual-mass flywheels (DMF) up to 260mm. This enables Borg & Beck to guarantee that its single-mass flywheels (SMF) can match the DMF specification as closely as possible.
Without question, the development of the Dual Mass Flywheel (DMF) Clutch has been a technological triumph and resulted in increased driver comfort and refinement. However, it also has its drawbacks, as it can be prone to problems related to the build-up of heat within the unit, as well as manufacturing costs being significantly higher compared to a standard Clutch Kit.
The complex DMF design makes it very difficult for the heat that is naturally produced during the normal operation of the vehicle to be dissipated through the two masses of the flywheel. This is because the friction plate is, in effect, only attached to the engine side of the flywheel through the centre bearing, which doesn’t allow the heat to be spread away from the friction plate efficiently.
These DMF issues are more of a problem for vehicles that cover high mileage, are driven at low speeds in the city or endure the demanding operating environment commonplace with taxis and LCV applications. When replacing the clutch in these applications, the best solution is a Single Mass Flywheel (SMF) kit.
The SMF kit is an original equipment (OE) designed product that allows the worn DMF and its associated Clutch components to be replaced with a traditional Solid Flywheel and Clutch Kit. This has been made possible by the development of the long travel damper, which uses advanced vibration clutch damper technology to create a damper capable of 40? of torsional movement, which is comparable with the movement that was typical of the equivalent DMF at the time of the vehicle’s original manufacture.
Technically, the SMF will reduce engine vibrations due to the increased inertia of the solid flywheel. In addition, the SMF is extremely durable, due to its efficient heat dissipation qualities and the lack of complex high wearing flywheel components.
The SMF is less expensive to manufacture and has the added advantage that the cost of a subsequent replacement is reduced further by the fact that the flywheel does not need to be changed with the rest of the clutch components.
As well as the cost advantages, the heat issues inherent with the DMF system are nullified when the solid flywheel replacement is fitted. This is because the traditional design of the system allows the heat to be absorbed through the flywheel and dissipated through the engine and flywheel housing in the normal way.
Therefore, the SMF offers a particularly suitable solution for vehicles where the original DMF is unable to dissipate heat effectively, but in addition, it offers greater longevity over DMF technology and is much more cost effective to replace.
Furthermore, a Borg & Beck spline grease sachet is included in every kit, as well as new flywheel bolts to allow workshops to benefit from the most straightforward fitting procedure.
The Borg & Beck Clutch programme includes 2 in 1, 3 in 1, 3 in 1 CSC, and SMF Kits, as well as Concentric Slave Cylinders and Hydraulic components which cover modern and classic applications, making it the preferred choice for factors and technicians.
Dual mass flywheels – a unique kind of flywheel – have been used on a variety of pickup truck and passenger car applications since the late 1980s. You’ll find them on 1987 Ford F-Series 6.9L diesels, 1992-96 Chevy 6.5L diesel trucks and 1992-02 Chevy 8.5L diesel trucks. Dual mass flywheels have also been used on some passenger car applications such as 1989 through 1996 vintage LT5 Corvettes, a variety of BMW, Audi, Porsche and Volkswagen models, plus some Hyundai and Nissan applications.
A dual mass flywheel is essentially two flywheels in one that provides some spring cushioning to dampen torsional crankshaft vibrations and shock loading when the clutch is engaged. Think of it as a flywheel with some “give.” In others, a solid disc is utilized and the dual mass flywheel provides all the dampening.
The two-piece assembly has a front “primary” flywheel and a rear “secondary” flywheel. The primary flywheel bolts to the crankshaft just like an ordinary solid flywheel, and has the ring gear for the starter. The clutch is bolted to the secondary flywheel, which is separate from the primary flywheel but attached to it with a series of coil springs mounted sideways between the two flywheels. The springs allow just enough movement between the flywheels to dampen the power strokes from a diesel engine so the vibrations are not felt throughout the drivetrain when the clutch is engaged. The cushioning effect also reduces shock loading on the transmission for longer gear life and less noise.
On gasoline-powered passenger car applications, a dual mass flywheel can provide the same kind of drivetrain cushioning and dampening for a smoother, quieter ride. A dual mass flywheel also helps smooth clutch engagement in vehicles with high torque output engines. It’s sort of like relocating the springs from the hub in the clutch disk further out so they can handle greater loads. Splitting the mass of the flywheel also reduces the rotating mass of the clutch assembly when shifts are made for smoother gear changes and reduced drivetrain noise.
Some dual mass flywheels use a slightly different design to achieve essentially the same end. Instead of relying solely on springs between the two flywheels to dampen vibrations and shock loading, a planetary gear set is used to control the motions between the primary and secondary flywheels.
DUAL MASS PROBLEMS Despite the functional advantages that dual mass flywheels have over conventional one-piece solid flywheels, some dual mass flywheels have proved to be troublesome and prone to premature failure. The dual mass flywheels in early Ford 6.9L F-Series diesel trucks have experienced a high rate of failure because of a weak spring design in the OEM flywheel. Spring fatigue and failure causes the flywheel to make a rattling or clunking noise when the clutch is engaged. Depressing the clutch pedal may cause the noise to go away. Debris from broken springs can also become trapped between the back of the flywheel and engine causing damage to the rear main oil seal housing and oil pan.
FLYWHEEL MOAN Another problem that has been reported is a vibration/moaning condition on some 1996-97 Ford F-250 and F-350 trucks with the 7.3L diesel engine and dual mass flywheel. Ford technical service bulletin #03-21-19 describes a moaning or vibration that can be heard or felt between 2,600 and 3,000 rpm. According to Ford, the cause is an imbalance between the engine, flywheel and clutch. The fix for this condition involves adding a stack of washers to one or more of the clutch cover bolts to change the balance of the rotating assembly. The idea is to add weight at various locations around the cover until the vibration goes away.
OTHER CAUSES OF FLYWHEEL FAILURES Premature failure of a dual mass flywheel can be caused by a variety of things other than normal wear and tear. The flywheel is engineered to handle a specific load, so if the engine has been modified to produce more power (turning up the boost pressure, for example), or adding a turbocharger or supercharger to a naturally aspirated engine, or nitrous oxide, the engine may produce more torque than the stock dual mass flywheel can handle.
Overloading the drivetrain by pulling more weight than the vehicle’s maximum towing or hauling capacity can also overtax a dual mass flywheel and lead to premature failure.
On diesel applications, anything that causes the engine to run roughly (bad fuel injectors, improper injector timing, loss of compression in a cylinder, etc.) may produce enough vibration to cause premature failure of the damper springs or nylon spacers inside a dual mass flywheel.
If a clutch starts to slip at low mileage, the problem may be a worn or defective “friction ring” between the primary and secondary flywheels. The friction ring allows the secondary flywheel to slip when torque loads are too high (to protect the transmission). The friction ring can wear out if excessive torque loads are continuously applied (as when overloading a vehicle and exceeding its rated hauling or towing capacity).
To check for a worn slip ring, block the engine so it cannot turn and partially insert two long bolts in the bolt holes on opposite sides of the clutch cover. Insert a pry bar between the bolts and try to rotate the secondary flywheel with respect to the primary flywheel. Most dual mass flywheels will have about 8 to 11 degrees of free rotational movement before the friction ring engages. If the secondary flywheel rotates with hand pressure, the ring is slipping and the flywheel needs to be replaced.
REPAIR OPTIONS Even if a dual mass flywheel does not experience a spring failure, the service life of most OEM dual mass flywheels is typically about the same as the clutch, which means the flywheel usually needs to be replaced when the clutch wears out. If you simply bolt in a new clutch, chances are your customer will have flywheel problems at some point down the road because of the weakened springs in the flywheel. That’s why many experts recommend replacing a dual mass flywheel when changing a clutch – especially if the flywheel has more than 80,000 or 90,000 miles on it. The flywheel should be considered a wear item just like the clutch, and should be replaced when a new clutch is installed.
Surface wear is another reason for replacement. The friction surface of a dual mass flywheel will wear the same as an ordinary flywheel as a result of normal clutch operation. The clutch surface may become rough, grooved or develop cracks or hard spots. Minor scoring and grooving is acceptable, but if the surface has hard spots, is warped or cracked, the flywheel must be replaced.
Resurfacing a dual mass flywheel with a rough or grooved surface is usually out of the question because of the two-piece design of the flywheel. To resurface a dual mass flywheel, the unit would have to be taken apart so the secondary flywheel could be remachined. The unit would then have to be “rebuilt” with new springs and reassembled with the same tolerances as before to work properly. Most of these units are not designed to be disassembled or serviced by technicians, so replacement is recommended if the unit shows a lot of wear or is making noise.
Dual mass flywheels are very expensive to replace. The list price for the flywheel alone is typically $800 to $1100. Add in a couple hundred bucks for a new clutch and clutch disk, plus labor to replace all the parts and you end up with a sizable repair bill.
A more affordable alternative is to replace the OEM dual mass flywheel with an aftermarket one-piece solid flywheel (which also requires a different clutch and clutch disk). In most cases, you can get a new flywheel and clutch for hundreds less than what it would cost to replace a dual mass flywheel itself.
When the one-piece solid flywheel replacement kits were first introduced for the early Ford and GM dual mass flywheel applications, some people said the kits would cause more problems than they solved. They said a solid flywheel would not provide enough dampening to protect the gears in the transmission from shock loading and would cause the transmission to fail. It never happened. By using a slightly larger clutch (13 inch as opposed to a 11 or 12 inch clutch in the stock dual mass flywheel) with redesigned hub springs in the clutch disk, the solid flywheel replacement kits proved to work just fine in these applications and caused no harm to the transmission.
For racing and high-performance applications, similar kits have been developed for Corvette, Porsche and BMW applications. These are mostly solid one-piece flywheels with stronger clutches and high performance or ceramic clutch disks, but there are some lightweight racing dual mass flywheels for BWM and Porsche.
FLYWHEEL R&R Replacing a dual mass flywheel may involve some extra work depending on the application.
A major part of these advancements is the direct result of smaller engines. Auto makers are now designing cars with three and even two-cylinder engines, and while these smaller engines have been successful in reducing fuel consumption, they are now being asked to provide the torque and power of much bigger motors. The result is a significant increase in vibration and noise, particularly at low speeds.
How did the automotive industry deal with this increased vibration and noise? The Dual Mass Flywheel.
A DMF acts in much the same way as a traditional, single flywheel – they provide direct contact between the engine and the clutch assembly in manual transmissions. Where DMFs differ from single flywheels is more than the fact that there are two flywheels as opposed to one - it’s what happens between the two flywheels that makes all the difference.
DMFs incorporate a series of springs between the flywheels and these springs act as vibration dampeners. Where vibration and noise in transmissions using a single flywheel has nowhere to go except directly into the powertrain system, a DMF’s spring system dampens this engine vibration, resulting in less noise, increased comfort for the driver, and increased life of the transmission.
What’s the downside? Having a DMF installed has generally meant higher maintenance costs for drivers. Clutch replacement has often required DMF replacement at the same time, and DMFs have traditionally been expensive and time consuming for workshops to install.
But some recent developments are making replacing DMFs much more affordable.
Major DMF manufacturers like Valeo are producing DMFs that are simple for mechanics to install and require no special tools, meaning significantly reduced fitting costs.
Valeo have also recently introduced a new type of DMF, the VBladeTM. Instead of a series of springs between the two flywheels, the VBladeTM utilises two vibration dampening blades. The result is an incredibly durable DMF that will mean lower maintenance costs for drivers.
Dual Mass Flywheels have proven to be so successful in reducing vibration and noise that now one in every two vehicles rolling off the assembly line is fitted with a DMF*. Chances are you have one on your car right now.
The idea is that the rubber creates smoother operation of the clutch release and reduces vibration in modern cars. The main reason these jobs tend to be more expensive than with typical older type clutch jobs is the price of the parts. A standard style flywheel is much more durable so does not often need to be changed.
Every car you see on the road has some sort of flywheel, and many of them have a dual-mass flywheel or DMF. It’s a crucial component, adding weight and momentum to the engine’s crankshaft to keep it spinning and smoothing out vibrations for quieter, more refined cars.
Different weights and sizes of flywheel are used depending on the type of engine and the car it’s installed in; as powerful, torquey turbo and diesel engines have become more popular in smaller cars, the dual-mass flywheel has stopped them being snappy, jerky or prone to breaking gearboxes prematurely. It’s also used to make cars more refined overall by damping small vibrations and encouraging the use of higher gears at slow speeds, for better economy.
If you think about how your car’s engine and gearbox are connected, the flywheel is connected to the clutch – and in the case of the dual-mass flywheel, there is almost always a clutch attached, as its purpose is to smooth out the torque and power of modern engines when putting drive to the road.
As a result, you will generally be aware of the DMF in smaller diesel manual cars where the vibration of the engine and amount of force it can generate when pulling away is enough to jolt and shake the car even when driven normally, and low speed refinement used to be poor. The DMF made these diesels more civilised and appealing from the mid-1990s on.
In technical terms, it’s a torsional damper – it performs the same task as the shock absorbers in your car, but on a spinning motion rather than a vertical motion. As the name implies, there are two masses – two flywheels – sandwiched together with a set of springs or rubber that allow an averaging of the rotation and torque coming from the engine (which is usually a set of pulses at high speed) and the gearbox’s rotation, which is usually smooth at a given road speed.
2The effect of dual-mass flywheens on vibration and refinement
The upshot of this is a car that is quieter and smoother to drive. It’s so effective that you’ll find dual-mass flywheels in cars with semi-automatic gearboxes or CVTs, and in those places it will often last a long time.
In a manual car, however, the driver can rev the engine hard and release the clutch abruptly. The dual-mass flywheel will attempt to smooth this difference, where a solid flywheel will usually cause the tyres or the clutch to slip. Over time, the DMF wears out from constantly absorbing that shock – but it is working all the time, even when not abused, to reduce vibration and noise.
Symptoms can include rumbling or squawk noises when chainging gear, shuddering when pulling away and in extreme cases, severe vibration and rattles when the car is in neutral.
On a test drive, if you’re particularly aggressive with the accellerator and clutch you may cause the DMF to ‘yelp’; if it does that with normal inputs then it’s starting to fail.
Some signs of dual-mass flywheel failure are shared with engine running problems, clutch, or gearbox failure but as investigation needs that whole area of the car stripping down, it’s more a case of being prepared for it being needed.
This handy guide from Sachs has some good tips on diagnosing and understanding dual-mass flywheel problems.
On many cars you can replace the dual-mass flywheel with a conventional one, but you may need to change the clutch, starter motor and other components too. Replacement of the flywheel can cost around £800 including labour, but they typically last as long as a clutch and the work involved to replace both components together is almost the same as replacing either one. For example, a common fitment – the Ford Focus 1.6TDCi which uses a joint-venture engine shared with many different marques – costs around £179-279 for the part.
"DMF or SMF which one is right for you?"
Which one is better and what are the pros and cons of conversion?
Why do manufactures install what appears to be an expensive and potentially unreliable dual mass Flywhee (DMF)?
What are DMF flywheels and why do people convert to solid ones?
The flywheel in a car helps to maintain the rotational energy from the engine.
This helps to avoid stalling and bogging down and makes it a lot easier to keep a car engine at constant RPM which is great for everyday driving and cruising.
Think of it as a buffer or reservoir. Without a flywheel every single fluctuation from the engine would be noticed. The gearbox and clutch would suffer from these shock waves, and the car would lose speed really quickly when you lift off throttle.
Firstly a DMF has two sections 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 so it rotates with a slight delay smoothing things out considerably.
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 these little blips.
The big benefit of a DMF is that the engine feels incredily smooth. 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.
The DMF is usually more expensive than a solid flywheel and due to complexity has more opportunity to go wrong.
They do not break up when they fail. They are more suited to conditions where frequent engine speed changes and gear changes are made.
They smooth out the engine causing it to feel silky smooth and this reduces wear on other parts of the transmission.
You really do need this in a diesel engine as they are quite rough running compared to a petrol engine. In smooth petrol engines they are nice to have. A DMF will also protect an engine as well as the gearbox from shock and vibration.
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. The solution would be to fit a stronger, higher performance DMF but the aftermarket industry seems geared up to offer solid ones as the upgrade option.
A solid flywheel replacement is often regretted by it's owner. They list vibrations and extra noise as the main issues. Gear changes appear to be required more frequently especially on hills.
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.
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 on other components.
If you do fit a solid flywheel you can help reduce some of the vibrations by fitting a carbon fibre drive shaft. Carbon fibre 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.
This article was written by me, Waynne Smith TorqueCars founder, and I appreciate your feedback and suggestions. This entry was filed under Engine Mods, Transmission, Tuning. You can leave a response below or join our forum to discuss this article and car modification in detail with our members.
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