Driving a vehicle with a manual transmission that has a dual-mass flywheel automatically creates a close relationship between you, the clutch pedal, and the transmission in a way that automatic transmissions simply don’t allow. It cultivates an intuitive sense of how the clutch and transmission are operating.
So, when the clutch starts to vibrate and then rattle, but the rattle then goes away, you press the clutch pedal all the way down, you know there’s something wrong. This experience can worsen if you also feel an increasingly rough idle or the car jerks violently when setting off in first gear.
These are all common symptoms of a dual-mass flywheel problem. Left unchecked, not only could it damage your transmission, but the repair bill alone can take a big bite out of your bank account. Of course, these symptoms can also mimic other engine, clutch, and transmission issues. So to find out if it truly is a failing dual-mass flywheel, we will have to take a closer look at some important technical details.
How Does a Dual-Mass Flywheel Work?
Dual-mass flywheels help to protect the drivetrain from the stresses of excess torque as well as engine torsional vibrations. These “Torque Pulses” commonly occur in heavy, manual transmission vehicles that have to do a lot of rapid shifting. The dual-mass flywheel is installed at the end of the crankshaft where you would normally find a traditional single,solid-state flywheel.
Dual-mass flywheels are more commonly paired with heavy-duty diesel engines and high-performance gasoline engines that produce a lot of torque. They help smooth out the gear changes and reduce the vibration of the engine idling, making the relationship between the engine, idling, and gear changes smoother. A dual-mass flywheel also helps reduce the torque pulsing and surging when towing and changing up quickly into a higher gear.
A dual-mass flywheel is made up of a pair of independent flywheels that are interconnected via a series of springs. The first flywheel is connected to the engine’s crankshaft. The second flywheel then acts as the friction surface for the clutch. The springs buffer the relationship between the two flywheels, dampening the engine’s vibrations while also keeping torque pulses from affecting the gears in the transmission.
6 Signs Of Dual Mass Flywheel Failure
If you suspect your vehicle has a bad dual-mass flywheel, look for a few common symptoms, such as jerking when going into first gear, vibrations in the clutch pedal, and rattling noises that vanish when you press the clutch pedal down. As the dual-mass flywheel continues to break down, you might notice.
1. A Stiff Clutch Pedal
A stiff clutch pedal that gets increasingly harder to press is one of the earliest signs of a dual-mass flywheel problem. This is a symptom of failing springs struggling to dampen the vibrations, which is translated to the clutch pedal.
However, this isn’t a standalone symptom of a dual-mass flywheel problem, as several other things can cause a stiff clutch pedal. Not the least of which is the clutch itself going out, a badly worn pressure plate, or even a failing clutch cylinder. So, you’ll have to be mindful of other potential signs that the dual-mass flywheel is failing.
2. Rattling Sounds Near the Firewall or Engine Bay
Strange rattling noises that sound like they’re coming from the firewall or the engine bay can also be a sign that the springs in the dual-mass flywheel have started to fail. Often, just a few springs wear out, impeding their ability to dampen the engine’s vibrations. This also places excess stress on the few remaining good springs, accelerating the speed as they wear out.
In many of these cases, the springs are starting to fail due to the lubricant inside the flywheel drying out. As it gets worse, the flywheel has a hard time rotating smoothly, causing a persistent rattling sound. You might also notice that this rattling sound temporarily vanishes when you press the clutch pedal all the way down, only to be replaced by physical vibrations.
3. Difficulty Shifting Gears
Difficult gear shifts are also a common early symptom of a failing dual-mass flywheel due to excess wear and tear caused by engine vibrations. As the flywheels start to wear on each other, shifting gears becomes harder and harder. At the same time, you’ll also start to notice unusual grinding and clunking noises as it finally changes up.
4. Shaking and Heavy Vibrations When Idling
A failing dual-mass flywheel can also cause increasing hard vibrations when idling as if it fails to buffer the twisting force of the engine’s crankshaft sufficiently. As the springs get worse, you’ll notice more shaking and vibrating in the car, which can feel like someone is banging on the transmission or the driveshaft with a hammer.
5. A Slipping Clutch
Imbalances and delamination in failing dual-mass flywheel can cause the manual transmission’s clutch to slip. This can lead to excessive heat build-up in the transmission as well as ineffective friction between the dual-mass flywheel and the clutch disc. As time goes on, both flywheels and the clutch disc wear out, and the transmission develops a nasty habit of slipping in and out of gears.
Early on, you’ll notice this trying to set off in first gear. You might feel a jerking motion as you engage and disengage the clutch. This problem will also be pronounced when you shift it into reverse and slowly start to let off the clutch.
6. Burning Smells
As a dual-mass flywheel continues to fail, the excess friction can start to burn out the clutch and clutch plate. Sometimes, this will show up as strange burning smells like a mixture of bread and oil. You might even notice a white puff of smoke or two in the engine bay.
What Causes A Dual Mass Flywheel to Fail?
While excess wear and tear can certainly damage a dual-mass flywheel manual transmission, other factors can accelerate the process, leading to premature failure. These include worn-out bearings, failing springs, friction heating from riding the clutch a lot, poor lubrication, or simply asking the car to do a lot of stop-and-go driving.
1. Overheating
If you frequently ride the clutch or drive in heavy stop-and-go traffic, the heat from friction can shorten the lifespan of your transmission’s dual-mass flywheel. In some cases, frequent overheating from friction can cause one or both of the flywheels to crack or warp.
2. Spring Failure
The springs in a dual-mass flywheel have a limited lifespan of roughly 75,000 to 90,000 miles. Though abusive driving habits, a lot of driving stop-and-go traffic, and frequently riding the clutch can speed up the rate of spring failure causing them to start to fail prematurely around 40,000 to 60,000 miles.
When the springs start to fail, they often cause strange rattling noises. Then, you often hear a “Clunk” when the clutch engages.
3. A Loss of Lubricant
Excess friction and heat can also cause the lubricant on the dual-mass flywheels to break down and dry out. This essentially accelerates the overheating problem and can lead to cracks and deformation of the shape of one or both flywheels.
4. High Mileage Wear & Tear
The springs and other components of a dual-mass flywheel have an average lifespan of 75,000 to 90,000 miles. This is also the average lifespan of a clutch, which is why many mechanics recommend replacing the dual-flywheel components when you replace the clutch.
5. Worn Out Bushings or Bearings
Worn-out bearings or bushings can quickly cause a dual-mass flywheel system to fail. This essentially allows the two masses to spin relative to each other without damaging the actual flywheels themselves. When a bushing or a bearing starts to wear out the two masses no longer spin correctly and can become imbalanced. While this can happen with natural wear and tear, bearing failures can be accelerated by excess heat from friction as well as a loss of proper lubrication.
6. Abusive Driving Habits
If you have a bad habit of always riding the clutch, making hard, quick gear changes, and getting stuck in a lot of stop-and-go traffic, it can decrease the lifespan of your dual-mass flywheels. These things place unnecessary stress on the flywheel. It can even cause the flywheel to crack or fracture in some severe cases.
7. Frequent Heavy or Overloaded Towing
If you frequently have to tow heavy loads or you have a bad habit of towing more than 80% of your vehicle’s rated maximum towing capacity, the excess force can wear on the dual-mass flywheels. The friction and forces applied to the flywheels and the other transmission components can be compounded if you also have a bad habit of short-shifting while towing.
How Do You Test for a Bad Dual-Mass Flywheel
If you’ve been noticing the telltale signs of a bad dual-mass flywheel, like rattling, a stiff clutch pedal, and vibrations when you’re in neutral, you usually have to remove it from the car to test it. However, there is a special dual-mass flywheel test tool. It’s sold at some auto parts stores and is often available via special order. Once you have it, you can use the DMF test tool and the following steps to determine if your dual-mass flywheel assembly is bad, or if there’s some other fault in your clutch.
What to Do When Your Dual Mass Flywheel Has Failed
Dual mass flywheels aren’t really engineered to be rebuilt or repaired. With most, the wisest option is to have it replaced. Since the mechanic is already tearing into the clutch, and the clutch likely has excess wear and tear of its own, it’s a good idea to replace it as well.
This will save you the long-term labor costs of having the clutch replaced in 10,000 miles or so. Especially if your clutch already has 75,000 miles or more on it.
Another option to consider is replacing the dual-mass flywheel with a single-mass flywheel, though this is usually something a professional mechanic should handle.
Replacing A Dual Mass Flywheel vs. Converting to A Single Mass Flywheel
It is possible to convert a manual transmission with a dual-mass flywheel to a single via a special conversion kit. This will change the driving dynamics of your car. You’ll often need to give the car more gas, and you’ll notice the gears feel different. You’ll also get more noise and vibration without the buffering of the springs of a dual-mass flywheel. Especially at low speeds.
However, single-mass flywheels tend to smooth out in higher gears at highway speed. They can also take more hard shifts without wearing out the way a dual-mass flywheel is prone to do. That’s one of the reasons why you see single-mass conversion flywheels in a lot of race cars, rat rods, and project cars.
Should You Convert A Dual Mass Flywheel To A Single Mass?
Converting a worn-out dual-mass flywheel transmission to a single-mass is a bad idea for a daily driver commuter car especially if you have to do a lot of stop-and-go traffic, moving at low speeds and RPMs.
You have also to consider that the average price for a DMF to SMF conversion kit ranges from $425 to $650 for just the parts. Then you’re looking at another $225 to $375 in labor costs to have it installed for a total conversion cost of $650 to 1,050. That’s all before making any replacement or repairs to the clutch.
Whereas having a mechanic replace the worn-out dual-mass flywheel and clutch costs around $850 to $1,200.
Frequently Asked Questions
Can you drive with a faulty dual-mass flywheel?
If your manual transmission has just started showing signs that the dual-mass flywheel is going out, you might be able to drive it for a while before you cause serious damage to the transmission. However, you’ll still be putting increasing stress on the clutch and could risk burning it out in the process. So, the wise move is to have the DMF replaced as soon as possible.
How long will a failing dual-mass flywheel last?
If your dual mass flywheel has just started to show signs of a problem, you might theoretically be able to drive it for another 2,000 or even 5,000 miles. However, you risk damaging the clutch and the transmission, leaving you with an even higher repair bill. If the DMF is in dire straits already, it’s best to park it rather than risk causing more major mechanical problems, especially if your daily commute involves a lot of stop-and-go traffic.
Should I change DMF with the clutch?
Most mechanics will tell you that the wise move is to replace the clutch when you replace the DMF. Especially if the clutch already has 75,000 or more miles on it, or you have to put it through a lot of stop-and-go traffic. The mechanic will already have to tear apart most of the clutch assembly anyway, so you’re saving yourself labor costs in the long run.
Can you replace a DMF with a normal flywheel?
There are conversion kits that will let you replace a bad DMF with a traditional single flywheel. However, there are drawbacks to this. You often have to give the car more gas as you shift through the tree, which hurts your MPG. It also tends to produce an uncomfortable amount of vibration. The biggest deciding factor with replacing a DMF with a normal flywheel is that the parts and labor end up being very similar to simply replacing the bad DMF with a new one.
How expensive is it to replace a flywheel?
The final cost to replace a dual-mass flywheel can vary, with an average cost between $850 and $1,200. Depending on the make and model, the part cost itself isn’t very high—usually between $85 and $300. However, some exotic models might have a much higher part cost, especially if it’s a rare foreign car maker that doesn’t have a wide parts distribution in North America.
The labor cost is typically the most expensive part of replacing a flywheel. Depending on the mechanic the cost to remove the old dual-mass flywheel and replace it with a new one can add an extra $450 to $700 to the final repair bill.
What cars have dual-mass flywheels?
Many cars with diesel engines have dual-mass flywheels to help reduce the engine’s vibration on the rest of the drivetrain and improve shifting performance. Dual-mass flywheels are also gaining in popularity in cars with gasoline engines. The Audi TT, the BMW 325, the Porsche Boxter, and the Chevy Corvette all have models with DMFs.
Conclusion
Symptoms of a failing dual-mass flywheel often start out as a strange rattling noise and vibrations in the clutch pedal. As the problem progresses, you’ll likely have an increasingly hard time changing gears, and/or the clutch will start slipping a lot.
Abusive driving habits and getting stuck in a lot of stop-and-go traffic can both accelerate the decline of a dual-mass flywheel. This can put excessive stress on the flywheel’s springs, bearings, and bushings and damage the clutch.
You can buy a special tool to test the imbalance and rock of your dual-mass flywheel without uninstalling it, though the cost can be prohibitive if it’s a one-off project.
There are conversion kits on the market that make it possible to replace a DMF with a single flywheel. However, the cost is on par with what you’d likely pay to replace the failing DMF with a new one. Replacing with a single flywheel can also affect performance and cause a lot of undue vibration.
Written By
Jason Farrell
Jason Farrell is a certified master technician, the editor of Mechanic’s Diary in Pittsburgh, Pennsylvania. He is ASE (Automotive Service Excellence) certified and earned a Bachelor’s Degree in Automotive Technology from Pittsburg State University. With nearly 18 prior years of experience in the automotive field, he has extensive knowledge about Domestic, European, and other foreign makes and models of cars and light trucks. Jason’s experience working as a technician and service manager at dealerships, gave him the experience and know-how of most aspects of inspection, diagnosis, and repair from engine and drivability to electrical, HVAC, brakes, steering and suspension and everything in between.