(Updated on November 3, 2020)
Every car with a manual transmission has a mechanical device called a flywheel. Flywheels are heavy, balanced metal disks that store rotational energy.
Since heavy spinning objects have high inertia (that is, resistance to change in velocity), flywheels keep your engine running smoothly even when torque delivery is inconsistent or changes quickly, such as when you’re shifting gears.
If you have only driven automatic transmission vehicles before then you have probably never heard of flywheels. Flywheels are usually only found in manual transmission vehicles.
Flywheels on cars and trucks are attached to the back of the engine between the engine and transmission. Flywheels provide an additional friction surface for the clutch and come with teeth that engage with the starter. When you turn the key, the starter motor turns the flywheel, which spins the crankshaft and starts the engine.
It is important for a manual vehicle to have a flywheel for gear changes and clutch engagement. Without a flywheel, the vehicle would likely stall when you engage the clutch to move the vehicle from a standstill. This is because the engine speed would drop too fast without all the angular momentum the flywheel provides.
If you could somehow drive your car without a flywheel, it would probably not be an enjoyable experience.
Bad Flywheel Symptoms
Unfortunately, flywheels do not last forever. They gradually become worn as they are consistently used in the vehicle. If your flywheel becomes too worn out or damaged, there will be some noticeable symptoms that you won’t be able to ignore.
Do not let these symptoms carry on for too long or else it will impact the overall drivability of the vehicle. Here are some of the most common signs of a bad flywheel.
1) Slipping Gears
If you shift to a new gear and then notice that the engine speed (RPM) increases much faster than your ground speed, this is called gear slippage.
Since the flywheel and the pressure plate both have friction surfaces that are designed to grip the clutch, a slipping flywheel may feel like a slipping clutch.
If oil or grease were to make its way onto the friction surface of the flywheel, it would impact the clutch’s ability to engage with the flywheel and grab it without slipping, even when the clutch should be fully engaged (with your foot off of the clutch pedal).
If the gear keeps slipping when you change it, then it will certainly impact your driving ability and eventually damage your clutch.
2) Cannot Change Gears
Sometimes you will have the opposite problem with your gears. Instead of your gears slipping, you won’t be able to change your gears at all. The flywheel would need to be in pretty bad shape for this symptom to occur, and other transmission components may be damaged as well.
Obviously, if you cannot switch gears, then you won’t be able to drive your vehicle at all.
3) Burning Odor
If there is a burning smell which consumes your passenger cabin, this could be attributed to many possible causes. A bad flywheel could be one of those causes because of all the heat generated from the friction in the clutch.
If you have used the clutch at times when you weren’t supposed to, this could cause problems with the flywheel.
4) Vibrations of the Clutch (Clutch Chatter)
If your clutch pedal is experiencing lots of vibrations, then your flywheel is likely going bad. The vibrations will eventually get so bad that you will be able to feel them on the floor rather than just from the clutch pedal.
As you drive your vehicle, the flywheel could end up with excessive runout over time, which leaves the surface feeling warped as you engage the clutch.
If you’ve ever overheated your flywheel or driven too long with a clutch that was on its last legs, it is very likely that you have damaged the flywheel due to excessive heat or metal on metal wear. Clutches that are worn down to the rivets will damage the flywheel.
A damaged flywheel may have a bluish color as the metal is heated far past its operating temperature. You’ll likely see some hairline cracks on the surface as well. There may even be smears of metal on the surface as the flywheel has heated and cooled.
Some flywheels contain springs, such as dual mass flywheels. If your car is equipped with one of these, the flywheel’s springs may be causing these vibrations. Dual mass flywheels will likely need replacement, as they cannot be resurfaced like a standard flywheel.
5) Unable to Start, or Inconsistent Starts
If the teeth on the flywheel are damaged, the flywheel may have trouble engaging with the starter motor. This could make it difficult or impossible to start the vehicle.
If you are having issues starting your vehicle, you may want to take a look at your starter as well.
6) Engine Stalling
An aftermarket flywheel that is too light for the vehicle (or the driver) will make it much easier to stall the vehicle and could give you a rough idle.
On very light flywheels, you may even stall the vehicle simply by pushing the clutch in, just because the engine speed drops too fast for the ECU to add additional air and fuel to compensate.
7) Engine Vibrations with Clutch Engaged
If a flywheel is unbalanced, it may vibrate the whole powertrain even while the clutch is engaged.
If you recently replaced the clutch, flywheel, or pressure plate, make sure you torqued all bolts to spec and applied thread locker if it was called for in the factory service manual. A flywheel that comes loose or disintegrates while driving is incredibly dangerous, as there is a considerable amount of energy stored in the flywheel.
The flywheel is very heavy and has the potential to shake the vehicle considerably if everything isn’t balanced and lined up properly.
Flywheel Replacement Cost
The replacement cost of a flywheel will depend on the make and model of your vehicle. You may get lucky and find the cost of a new flywheel to be only $40 or so. However, there are some flywheels which will cost up to $400 or more which are made up of stronger and lighter materials than just steel. Dual mass flywheels or other complicated implementations are more expensive.
On top of the parts cost, you’ll have to worry about the cost of the labor too. This will not be a short job to perform, so the mechanic may be spending close to 4 to 5 hours. If their hourly rate is $100, that would mean $400 to $500 just for the labor costs.
Add the totals together and you are looking at around $400 to $1500 for the total cost of getting the flywheel replaced, depending on the vehicle.