If you drive a car with a manual transmission, perhaps you’ve wondered exactly how it works. Most people are familiar with the major components of the powertrain, including the transmission, the engine, the differential, but far fewer people understand how these components connect in order to deliver power to your wheels. One of the most important components required to transfer power from your engine through your transmission is the flywheel.
Function of a Flywheel
The ultimate goal within an engine is to make the crankshaft turn as a result of the combustion process. All other major components within an engine exist to support this primary goal. In other words, crankshaft rotation is the primary output of a motor. Attached to the rear of the crankshaft is the flywheel.
Due to the fact that they are directly connected, the flywheel spins at the same speed as the crankshaft. The flywheel is the disc shaped component that the clutch comes into contact with when engaged that allows the energy output from your engine to be transferred to your transmission.
In order to understand how a flywheel works, it’s important to understand how a clutch in a manual transmission works. A clutch is essentially a disc with a friction surface on it that is connected to the input side of the transmission that can be engaged and disengaged by depressing the clutch pedal. When the pedal is pushed down, the clutch disc is disengaged, and when you release the clutch pedal, the clutch is engaged.
When engaging the clutch (releasing the pedal), you are essentially pressing the clutch disc against the spinning flywheel. Due to the friction surface on the clutch, when the clutch comes into contact with the flywheel, the clutch experiences rotational acceleration until it’s speed matches that of the flywheel. At this point, the output of the engine is directly connected to the input of the transmission as the clutch and flywheel have stopped slipping against each other and are now spinning in unison. When you disengage the clutch (press the pedal), you break this connection which allows you to coast in neutral and shift gears more easily.
The flywheel also has one other function, which is to assist in starting the vehicle. The flywheel has gear teeth around its circumference. The starter motor is positioned such that the starter motor gear engages the teeth on the flywheel. When you turn your ignition on and the starter motor spins, it spins your flywheel which, by virtue of the direct connection to your crankshaft, also spins your motor allowing it to eventually turn over and start.
Common Symptoms of a Bad Flywheel
The clutch flywheel is an integral part of the manual transmission system. There are general signs or symptoms you can detect that will tell you when the flywheel needs to be inspected or potentially replaced. It should also be noted that many of the common symptoms of a bad flywheel are also symptoms of a bad clutch or related components. Considering the amount of work required to replace either component, most often the flywheel and clutch are replaced at the same time. The following are the most common issues:
Hot Spots On Flywheel – Because the flywheel and clutch are subject to heat created by the friction between the two components, hot spots can occur on the flywheel under certain heavy driving conditions, due to poor manual transmission driving habits, or due to clutch component failures and wear. Hot spots are essentially portions of the flywheel that have been overheated, which can create rough spots that significantly reduce clutch life. In addition, flywheels with hot spots are far more likely to be warped. If you have a single mass flywheel, sometimes you can reface the flywheel to save a few bucks. Due to the construction of dual mass flywheels which are more commonly found on modern vehicles, hot spots are typically reason for replacement as this type of flywheel is much more difficult to reface. Hot spots are typically noticed incidentally by a mechanic during a clutch replacement.
Vibration And Chatter – If a flywheel becomes sufficiently warped due to heat, it can cause a vibration when the vehicle is running and the clutch is engaged. It is often most noticeable when switching gears, as it can sometimes be felt in the clutch pedal itself. Often times, this vibration is accompanied by chatter or sounds most noticeable when shifting gears.
Grinding When Starting the Vehicle – When you start your vehicle with a manual transmission, the starter gear engages with the ring gear on the circumference of the flywheel. If the teeth are worn on the flywheel ring gear, it may make a grinding noise and not engage with the starter correctly. If the ring gear on the flywheel is damaged to the point where teeth have chipped completely off, you may notice intermittent issues where the starter won’t spin the flywheel at all because the starter gear can’t engage the flywheel when the gear is aligned with a portion of the flywheel that is missing gear teeth.
Replacing a Flywheel
When you detect an issue with the flywheel, it may be time to inspect for a problem and potentially replace the flywheel. Most often, considering the amount of work required to inspect the flywheel, mechanics choose to replace it either way along with the clutch since most of the cost in the project is associated with labor rather than the cost of components. Due to the fact that the procedure for replacing a flywheel is pretty involved, we are going to cover only the more major steps to give you an idea of what you’re signing up for. Additionally, the procedure for a rear wheel drive car differs significantly from a front wheel drive car.
Note: The example steps below are intended for general informational purposes solely to help give you an idea of project difficulty and tools required. As all cars are engineered differently, repair procedures and safety hazards vary from vehicle to vehicle. To ensure that you have a vehicle specific repair procedure and an exhaustive list of potential safety hazards, we advise you reference a factory service manual for your vehicle. Similarly, referencing a repair manual such as Chilton or Haynes might serve as a less expensive alternative.
Step 1 – The first thing you’ll have to do with both a FWD and RWD car is raise it up in the air. To accomplish this, you will need a good floor jack and an appropriately rated set of jack stands. Alternatively, you could also opt to use a set of car ramps for a rear wheel drive car. If using a floor jack and jack stands, make sure you are utilizing the vehicle’s designated lifting points, as described in the owner’s manual. As you may be working with electrical components, such as the starter, you should also disconnect the negative battery cable to avoid electrical shock.
Step 2 – For rear wheel drive cars, you will have to disconnect the drive shaft. This may require a socket and ratchet set or a set of combination wrenches. The bolts fastening the driveshaft to the transmission may be extremely tight, so you may consider spraying on some penetrant and letting them soak for a little while before removal. You may also benefit from the use of a breaker bar to help break the bolts loose more easily.
For front wheel drive cars, you will have to remove the CV axles. This will require you to remove the wheels and likely some of the front suspension components. You will need to separate the ball joints, which can be accomplished with a ball joint separator.
Essentially, you have to remove everything connected to the transmission before it’s ready to come out.
Step 3 – Once everything is disconnected, you will have to remove the transmission. For rear wheel drive cars, you will need support the transmission using a transmission jack, remove the crossmember for the transmission, unbolt it from the motor, and lower it using the transmission jack.
Front wheel drive cars tend to be more varied since the working space is tighter. Often times, you will need to remove the entire engine and transmission assembly (which includes disconnecting all the other stuff from the engine to allow this) from the car before removing the transmission from the engine. For this task, you will need an engine hoist.
Step 4 – Once the transmission is separated, you can remove the clutch next. This requires a socket set and sometimes a breaker bar. Once the clutch is out of the way, you can unbolt the flywheel.
Step 5 – Reassembly occurs in the reverse order that components were removed. Before reassembling, this is a good time to check your rear main seal for leaks. If leaking, you should repair it. To reinstall the clutch, you will need a clutch alignment tool. This is a good time to consider replacing your clutch, throwout bearing and pilot bearing if they are worn to save yourself some labor in the future as these parts are relatively cheap. As a safety matter, you will need to make sure all bolts are appropriately torqued to spec, which can be achieved using a calibrated torque wrench with the appropriate torque range. If you had to drain any fluids such as your oil, make sure you replace them.
Step 6 – Once everything is reinstalled and you are sure your vehicle is safe to drive, you can take it for a spin to confirm that the repair was performed correctly. If you notice anything out of the ordinary, stop immediately, trouble shoot, and repair the issue.
Best Flywheel Brands
When it comes to selecting a replacement flywheel for your vehicle, there are many quality brands to select from. To help narrow your search, we have provided three brands we recommend as we have found them to be a good balance of quality and value over the years.
Sachs produces both stock replacement and high-performance flywheels depending on your application. In addition to flywheels, Sachs is also well known for making clutches, as well as suspension components and torque converters for automatic transmissions. Sachs flywheels are made to high quality standards, and the pricing for their components is affordable, especially considering the quality. Overall, we think you’ll be pleased if you decide to install a Sachs flywheel in your vehicle.
Click here to find a Sachs flywheel for your vehicle.
Luk produces a line of replacement flywheels that are functionally tested to meet or exceed OEM specifications. Luk is an OEM supplier and also develops performance specifications for individual vehicle applications. Each flywheel component and assembly is engineered and manufactured for reliable performance and the attractive pricing makes Luk a high value proposition for your flywheel replacement project. Overall, you will be in good shape if you opt to install a Luk flywheel next time you are due for a replacement.
Click here to find a Luk flywheel for your vehicle.
Fidanza offers OEM replacement and performance flywheels. They make aluminum flywheels as well as steel flywheels, so it is reasonable to expect that Fidanza will have a flywheel option that suits your vehicle. In addition to the flywheels, they offer complete matching clutch assemblies for most vehicles, adjustable camshaft gears, and other performance parts. Fidanza is a well known company among car enthusiasts, and we are confidant that you will be satisfied if you choose a Fidanza flywheel.