Dual mass flywheel – the bane of everyone’s existence when it fails, but the only thing that’s keeping your commute somewhat enjoyable when it’s working as intended. These mechanical devices used to be found only in cars with larger displacement engines, but nowadays, they’re everywhere.
Today we’re going to learn what this component does, how to recognize a failing DMF and what you can do as a driver to avoid any issues in the future.
What is a Dual Mass Flywheel and What is its Purpose?
If we remove electric cars from the equation, just about any motor vehicle out there requires an engine to create power and a drivetrain to deliver said power to the wheels.
In our endless search for improved efficiency, we’ve started creating smaller but more powerful motors that deliver high amounts of torque. This is especially true for modern diesel engines, which are extremely popular in places like Europe.
By squeezing more power out of a small engine, engineers across the industry have run into a fairly serious issue – these new engines are creating way too much vibration and harmonics for the drivetrain to handle.
Internal combustion engines found in cars today use four strokes to create power. You’ve got intake, compression, combustion, and exhaust. That means that you’re getting one power stroke for every 180 degrees of crankshaft rotation. If we were to graph this, we’d see a high-frequency power wave where harmonics peak at each power stroke only to dissipate in between two power stroke cycles.
In other words, the power created by the engine isn’t smooth. Those vibrations are transferred to the entire drive train, which is often not built to withstand such forces over a prolonged period, especially with high torque figures. One way to eliminate or at least minimize these harmonics is to use a dual mass flywheel.
The Insides of a Dual Mass Flywheel – Springs
What is the best way to eliminate vibrations in any system? Dampening. A dual mass flywheel is based on two separate masses and a set of dampening springs that connect them. Aside from these springs, the two masses are entirely free to move independently from one another. When the clutch is released, and the powertrain starts sending power to the wheels, the two masses meet and start rotating together.
By having the springs between the primary and secondary flywheel mass, you’re essentially soaking in most of the torsional vibrations from the engine and putting out smooth power to the transmission and the rest of the drivetrain.
Recognizing Dual Mass Flywheel Failure
Just like most other mechanical systems that are constantly under stress, DMFs tend to fail from time to time. Years of use will leave a mark on any of the clutch components, let alone a fairly complicated system such as the dual mass flywheel assembly.
Fortunately for us, it is rather simple to recognize a failing DMF long before it reaches a stage where it can impact the performance of your car. Here are several things to look out for.
Excessive Vibration on Engine Shutdown
One of the easiest ways to tell if your DMF is on its way out is to check for vibrations when you turn off the engine. What you’re looking for is a sensation that the drivetrain needs a moment to settle down once the power to the engine is cut.
Truth be told, this can also be due to faulty engine mounts, but more often than not, such vibrations are a dead giveaway that your DMF is about to go.
Vibrations During Acceleration
Next up are vibrations that occur as you accelerate, especially in the lower RPM range. A fully functioning DMF will offer smooth acceleration with very little or no vibrations at all, depending on your engine. A failing unit won’t react well to low-end torque and will cause excessive shaking and vibrations as you let off the clutch and apply the gas.
Clunking or Spring Noise While the Car is in Neutral
Additionally, you’ll find that failing DMFs tend to produce an irregular clunking noise while the car is in neutral. This type of noise is often called ‘DMF death rattle’ and is something you definitely don’t want to hear when you start the car in the morning.
What Causes Dual Mass Flywheel Failure?
Before we get into specific ways these units fail, we have to clear one thing up – DMFs wear out over time. It’s just how things are. You can count on having to change your flywheel at around 100,000 miles depending on your car’s make and model.
With that said, DMFs can fail much sooner than that if you’re not careful. As a matter of fact, you can take a 2019 manual car and abuse it to a point where you’ll cause DMF failure in less than a year.
The key to a long lifecycle of this part of your clutch system is to know what not to do during your everyday commute. Here are a few things that cause DMF failure:
- Aggressive Acceleration – To start things off, let’s talk about flooring your car from a standstill. Even though just about every car is capable of launching from a standstill, most are not designed to endure frequent aggressive acceleration. By flooring it on every stoplight, you’re putting excessive strain on the springs that connect the primary and secondary flywheel masses. Additionally, your clutch will also suffer. Do this enough times, and you’ll hear that death rattle sooner or later.
- Using a Higher Gear than Recommended – We’ve all been in that situation where you’ve slowed down to 25mph but didn’t downshift into 3rd gear. Using higher gears at low speeds is a good way to put unnecessary strain on the DMF and the springs assembly inside. If you do this excessively, you might want to schedule a visit to your mechanic soon.
- Engine Tuning – Modern turbocharged engines bring plenty of headroom for upgrades. This is especially true when tuning turbo diesel engines. With so much potential that can be unlocked with a simple ECU remap, it’s not uncommon to overload the gearbox to the point of failure. One of the first things that goes is usually the DMF. Even though they too can handle a bit more torque than specified, an average DMF isn’t won’t survive an aggressive remap. Because of that, you need to be extremely careful with your engine tuning.
Converting Dual Mass Flywheels to Single Mass Flywheels
Since replacing a DMF is no cheap affair, many are considering simply converting their dual mass flywheels into single mass flywheels. The idea here is to simplify the entire assembly and make the clutch system more robust and durable. But does this always work?
The issue most of these conversion kits bring to the table is the lack of vibration dampening – the very thing DMFs were invented to counter. If the whole problem came down to ride comfort, there are undoubtedly many people out there who would rather have a more reliable car in exchange for a shaky idle. However, it’s not just the ride quality that’s the issue here.
Letting all of those vibrations reach the transmission can cause serious problems. You’re looking at potential gearbox damage and a whole bunch of other potential issues.
Naturally, this doesn’t apply to all cars. Some models will easily accept a single mass flywheel conversion kit and work just fine, but for some, that would be the last straw.
If you decide to go ahead with the conversion, make sure that you have all the facts. The last thing you want to do is invest, tear down your transmission, and pop the clutch out only to find out that your plan won’t exactly work after all.
At the end of the day, DMFs have proven to be a necessary evil that keeps things running smooth. Taking good care of your car will be more than enough to prolong the lifespan of your flywheel and postpone that expensive swap job. However, if you recognize some of the symptoms mentioned above, don’t hesitate to get flywheel fixed. Ignoring this issue can only create cause more problems down the road.