Flex plate diagram

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What's the Difference between a Flywheel and a Flexplate in Diesel Engines?

flywheel diagram clutch disc pressure plate | Highway & Heavy Parts


We get a lot of people wondering what the difference is between flywheels and flexplates.

While flywheels and flexplates have similarities, they are not the same. People often refer to them as the same part, but while flywheels and flexplates help accomplish the same task, they do it in different ways.

This depends on whether its an automatic or manual transmission.


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What's a Flywheel For? 

Flywheels are used to mount clutches on manual transmission vehicles.

A manual transmission has a flywheel that is attached to the crankshaft and has a clutch disk in between the pressure plate and flywheel.  The flywheel is connected directly to the clutch, allowing torque to transfer between the transmission and the engine. The flywheel can provide a friction surface for the clutch to contact.

Needing to replace your crankshaft? Check out our crankshaft installation guide!

Myodesie.com shares the three functions of a flyweel: "First, through its inertia, it reduces vibration by smoothing out the power stroke as each cylinder fires. Second, it is the mounting surface used to bolt the engine up to its load. Third, on some diesels, the flywheel has gear teeth around its perimeter that allow the starting motors to engage and crank the diesel."

A flywheel is a heavy wheel that takes a lot of force to spin around. When it's spinning at high speed, it can store a great deal of kinetic energy. Its job is to store rotational energy that produces power to the transmission. It has a good bit of mass to store energy to keep the engine turning between pulses at idle.

Flywheels vary in size. It could be a large-diameter wheel with spokes and a very heavy metal rim, or it could be a smaller-diameter cylinder made of a carbon-fiber composite sometimes with steel rims.

Their life cycle can outlast that of the clutch, but if you're installing a new clutch, it will need to be resurfaced.


Signs of a Bad Flywheel

There are some signs and symptoms to look for that will let you know when the flywheel needs to be replaced. Here are 3 common signs:

  • A burning smell: This smell comes from too much heat produced by the clutch facings. "Riding" the clutch while driving causes this burnt toast odor. This causes the flywheel to wear out prematurely. 
  • Gear slippage: You'll notice this while you're driving. If the transmission can't shift to the next gear, it will slip into the previous gear. When caused by a bad flywheel, gear slippage causes plate grinding, and the driver or a mechanic may find small metal shavings in the transmission fluid.
  • Clutch vibrations: You'll feel this in the passenger compartment of the car while driving. They are typically caused by the spring mount mechanism on the flywheel failing, and will greatly reduce the flywheel's performance when the driver depresses the clutch.


What do We Need a Flexplate For?


flex plate diagram engine components | Highway & Heavy Parts


Flexplates are used to mount torque converters on automatic transmission vehicles. 

Torque converters replace the clutch of a manual transmission. A flexplate is mounted to the crankshaft and connects the output from the engine to the input of a torque converter. The torque converter is located between the flexplate and the transmission.

A flexplate is typically a stamped steel disc with a ring gear welded on that mounts the torque converter to the rear of the engines crankshaft. Flexplates are generally much thinner and lighter than a flywheel because of the elimination of the clutch surface.

The metal frame of the flexplate has multiple uniform machine-cut holes for mounting to the crankshaft. The other holes are specific to the vehicle, torque converter set-up, and potential weight balance of the flexplate.

While there are some exceptions, if your vehicle has a manual transmission, you want a flywheel, and if your vehicle has an automatic transmission, you want a flexplate.

Need help with your diesel engine? Our ASE Certified Techs have answers for you! Call them at 844-304-7688. You can also request a quote online!


Originally posted October 8, 2015; Edited September 24, 2019

Sours: https://highwayandheavyparts.com/n-12101-flywheel-versus-flexplate.html


Automatic Transmission


The flywheel for most automatic transmissions/transaxles is simply a stamped-steel disc with a ring gear located at the outer edge for engagement with the starter’s pinion gear. With this type of flywheel, the torque converter has no ring gear. Some cars use a more modest flywheel known as a flexplate, which is all that’s needed because the torque converter itself has a ring gear located on its outer edge.


The flywheel, or flexplate, mounts to the engine's crankshaft and also serves as a mounting location for the torque converter. Consequently, the flywheel or flexplate transmits engine torque to the torque converter housing. The flywheel’s ring gear also serves as an engagement point for the pinion of the starter motor when cranking the engine. Because of the lightweight design of the flywheel or flexplate, it does not help to smooth out power pulses from the engine like the flywheel does on a car with a manual transmission. On cars with automatic transmissions, the torque converter provides this function.

Maintenance Tips/Suggestions

The flywheel/flexplate does not require regular maintenance. Sometimes, the ring gear may suffer damage from improper starter engagement or alignment. If this is the case, the ring gear or flywheel may need replacement.

Sours: https://www.mastermechanic.ca/inspection/flywheel-flexplate.php
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Flexplate vs Flywheel – 3 things you need to know [Most important]

Often referred to as being the same thing, flywheels and flexplates have similarities but are quite different.

AKMI' Product: K-21514061 Aftermarket Volvo D11 Flywheel1. Flywheels are typically found on vehicles equipped with manual transmissions, while flexplates are used in vehicles with automatic transmissions.

A manual transmission has a flywheel that is attached to the crankshaft and has a clutch disk in between the pressure plate and flywheel.

When someone presses the clutch, the throwout bearing is pushed in, which forces the pressure plate to stop applying pressure to the clutch disk.

As this happens, it stops receiving power from the engine.

So the gear shifts without damaging the transmission.

Once the operator/driver shifts into a new gear release the clutch pedal then the clutch disk is allowed to start receiving power from the engine once again.

Automatic transmissions eliminate the clutch and grinding.

Basically automating the shifting process so the driver does not have to worry about shifting gears while driving.

A flexplate is mounted to the crankshaft and connects the output from the engine to the input of a torque converter.

Torque converters replace the clutch of a manual transmission.

Allowing the load to be separated from the power source.

They are generally a type of fluid coupling that can multiply torque and is used in transferring rotating power from the prime mover (internal combustion engine or electric motor) to a rotating driven load. The torque converter is located between the flexplate and the transmission.

Flywheels, due to the friction process, are very thick, made of steel and are as heavy as they look.

Their lifecycle can outlast that of the clutch but will need resurfacing before installing a new clutch.

When they need do need replacing, you can typically get away with using an aftermarket replacement.

2. Flexplates are much thinner than a FlywheelAKMI' Product: AK-3973497 Cummins ISC ISL Flywheel

As well as the ring gear it uses to connect with the starter (depending on vehicle and engine size), and are much, much lighter.

This is due to the fluid coupling of the torque converter, which eliminates the grinding of a clutch.

The lighter, thinner metal frame has an ability to flex across its main axis – bending side to side (hence the name Flexplate) – taking up motion in the torque converter as the rotational speeds change.

The metal frame of the flexplate itself will have multiple machine-cut holes within the body of the plate.

One set of holes will look uniform and would be for mounting to the crankshaft.

The other holes are specific to the vehicle, torque converter set-up and potential weight balance of the flexplate.

No matter the car size, small economy size or heavy-duty truck.

If your vehicle has a manual transmission and you have to step on the clutch to shift gears,

your vehicle has a flywheel as part of your transmission. If all you have to do is put the shifter in a drive (D) and step on the gas pedal, your vehicle has a flexplate.

AKMI' Product: Mack MP7 flywheel diesel trucks

3. Repair and replacement cost

If you have problems with your flywheel you probably have to replace them, but what it´s their costs?

The replacement of the flywheel can vary depending on the model and the quality,

the prices are about 35$ and 400$. In our shop, we have a variety of flywheels for your comfort.

Those were some important facts about flywheels and flexplates.

Now, can I drive with a cracked flexplate?

Sure you can drive with a broken flexplate but is heavy dangerous.

And the sound of the broken part is terrible if you have a broken flexplate or flywheel you have to go to your mechanic immediately and change the part.

Sours: https://akmicorp.com/flywheel-vs-flexplate/

Flexplate – What Does It Do?

What is a Flexplate?

Situated between the engine of a motor vehicle, and the gearbox and transmission mechanism, is a clever and essential device that has been fitted to engines of all shapes and sizes since the early days of steam locomotion up to high performance vehicles of the present day. That device is known as a “flywheel” and its somewhat more recent counterpart, which is fitted to engines within vehicles with an automatic transmission, is known as a “flexplate.”

Their roles in the task of driving a motor vehicle forwards, (or backwards for that matter), are virtually identical but it is the specific function of the flexi plate that we are discussing in this article.

Car Engine

Flexplate: What Does it Do? – Back to Basics

The basic principle behind flexplates, and their manual transmission counterparts, flywheels, is to store the energy that is generated by the engine until it is needed and to deliver it in a smooth and even way via the vehicle transmission system, (gearbox) to where it is needed, which is ultimately in the wheels of an automobile, in order to propel the vehicle along.

Internal combustion engines are very powerful but the power that an engine generates is not completely smooth. This is because the firing process comprises of several different actions that, despite happening very quickly, do not happen simultaneously. The power generated by the engine therefore is not smooth but it needs to be so because if it wasn’t the “ride” of the vehicle would be rough and uneven – quite unpleasant for an automobile.

The flexplate effectively captures the energy that is created by the engine and stores it in its large mass by spinning at a speed that, although it is not required all the time, is smooth and even.

The energy held in the flexplate/flywheel is transferred to the gearbox and transmission by means of a system called a torque converter which broadly is the equivalent of a clutch on a manual transmission vehicle.

The role of the torque converter is to replace the clutch on a manual transmission vehicle. In this case, the flexplate would be mounted to the crankshaft of the engine in order to transfer the output (energy) from the engine to the torque converter. The configuration would be for the torque converter to be located between the flexplate and the automatic gearbox unit.

Flexplate vs Flywheel – Some Important differences

The design of a flexplate is somewhat different to that of a flywheel although they are in essence the same thing – a large wheel that spins at high speed to even out and store energy that is generated by the motor.

Whereas a flywheel is a heavy wheel, a flexplate is usually a somewhat lighter and thinner stamped steel disc fitted with a ring gear welded that couples the torque converter to the engine’s crankshaft. The reason that flexplates are generally much thinner and lighter than a flywheel is due to the fact that the clutch surface that would be found on a conventional flywheel is not required for an automatic transmission as there is no clutch involved.

The flexplate will normally have a variety of holes drilled into its surface which perform various tasks. Some of these holes are to facilitate mounting the flexplate to the crankshaft whereas the others are for torque converter settings and weight balancing – very important for a spinning object in order to avoid bumps and unevenness. Because of the balancing aspect of the flexplate it is important that, when removed for servicing, the flexplate must be replaced in exactly the same position.


What is the “Flex” in Flexplate?

The inclusion of the term “flex” in the name flexplate implies some kind of flexibility and this is another important aspect of a flexplate that differs from that of a flywheel, which is rigid.

The flexplate is made from a sheet of fairly thin stamped steel whereas the flywheel is heavier and solid. The flexibility of the flexplate enables it to adjust to slight misalignments between the engine and the transmission without causing it to crack or otherwise damage the parts involved. A flywheel doesn’t need this amount of flexibility since it is decoupled from the engine by the clutch when the driver changes gear.

Just to put this “flexibility” into context it should be remembered that you cannot manually flex a flexplate – this will normally only occur when the considerable forces of a powerful engine causes the flexplate to spin at high speeds and the torque convertor comes into play in order to change the gear in the automatic gearbox.

Bad Flexplate Indications

How can you tell if something is not right with your flexplate or transmission system?

There are a few indicators that the layman can use in order to determine whether the flexplate has developed a fault or become damaged.

Firstly, when starting the engine, pay attention to the noise made by the starter motor when it spins and engages with the flexplate, or with the torque converter if the vehicle is not fitted with a toothed flex plate. If the starter makes a whining noise while spinning that can indicate a flexplate problem.

Also listen for any rhythmic clunking or grinding noise while the engine is idling in neutral or park. If a bolt has broken or become loose, on the flexplate, these can misalign the flexplate and cause the side of the plate to come into contact with other components. If the flexplate becomes warped this can cause metal-to-metal contact with the cover, or the starter drive mechanism, and can also make a knocking noise once the vehicle is put in forward or reverse gear.

Bad vibrations – if, when driving the vehicle, you notice vibrations that may gain in severity as the speed increases then this can indicate a flexplate fault – sometimes pointing to a balancing weight that has become dislodged.

Other Flexplate Problem Causes

Flexplate malfunction can be caused in several ways, some of which require a well-equipped workshop in order to diagnose but some common ones are:

  • The engine or torque convertor is out of balance.
  • A fault on the starter drive sometimes causes teeth or the ring gear to wear rapidly or snap.
  • The flexplate bolts have not been set for the correct torque settings and tightened in the specified sequence.

If your vehicle develops a flexplate problem you will probably require the services of a trained mechanic with suitable tools and equipment on order to rectify that problem. Replacing/repairing flexplates is generally not a job for an amateur.


  1. Flexplate – What Does It Do ? – What Happens When It Fails – Danny’s Engine Portal
  2. What is a flex plate in Ann Arbor MI – Ron’s Garage
Sours: https://www.carbibles.com/what-is-a-flexplate/

Diagram flex plate

The last 60 years of hot rodding has experienced a wide variety of engine combinations that can be used to power your project. The choices between big blocks, small blocks, Y blocks, Hemi, LS, Cleveland, and Windsor can be a little mind-boggling sometimes, but typically we all have our favorite that we wouldn’t trade for anything. The big three automakers all had dreams and visions of what would make the ultimate power plant to propel their cars and trucks down the road. Some were revolutionary and some were better suited as boat anchors. Regardless of which engine is your favorite, it’s important to know how your engine is set up to work with the wide variety of transmissions available today. One of the biggest challenges you may face is learning exactly how your engine balance is set up to ensure that the correct flywheel or flex plate is bolted on the first time. Some of you may be thinking that this seems pretty elementary, but you’re not alone if you just aren’t 100% sure of what you’re working with.

The focus of this article will be on the more popular V8 applications you see used in abundance throughout hot rodding. If you have something you don’t see listed here, there will likely be a little more research to be done in determining whether or not you’d need a custom-built flywheel or flex plate to accommodate your chosen combination. In addition to the importance of engine balance there are two other important factors to consider: your crank flange bolt pattern/sealing arrangement, and your ring gear tooth count. These are the critical elements to making sure you are able to properly attach your engine to your chosen transmission.

Each engine family has its own specific set-up, so the critical first piece of information is knowing exactly which engine you’ll be using. This is especially important because not everyone refers to things the same way.  Two engines might both be part of the “small block” family, but are completely different when it comes to which flex plate or flywheel they use. You’ll want to gather as much possible information as you can before you set out on your parts-gathering journey, so that you can find the right parts in one trip! 

Let’s begin with the GM stuff, since those are fairly common and popular engines used in the hot rod community. The crank flange bolt patterns of Gen I (two-piece rear main seal), Gen II (one-piece rear main seal), and Gen III, IV, V (LS style) are all different and will not permit any interchange between them. These bolt patterns became successively smaller with each generation. Gen I and Gen II Chevy engines featured two available diameters of flywheels / flex plates and two corresponding tooth counts of 153 and 168. Gen III, IV, V LS/LT series engines feature only the large diameter, 168 tooth flywheels and flex plates, but carry either a 6, 8, or 9 bolt crank flange.

Early GM(Chevrolet) Small Block Engines

  • Built from 1955-1985
  • Displacements were 265c.i. up to 400c.i.
  • 2pc rear main seal design crank shaft with 6 bolt flange
  • 153 tooth and 168 tooth ring gears- many of the factory bellhousings will only accept the 157 tooth size, typically the aftermarket bellhousings will accept both sizes.  In many cases if you’re changing from one size to the other you will also need a new starter that is paired for that ring gear
  • All had an internal or “0” balance

Late GM Small Block Engines

  • Built from 1986-2003 for factory vehicles, still available through GM’s crate engine program
  • Displacements were limited to 305c.i. or 350c.i. (the L99 262c.i. was a rare exception)
  • 1 pc rear main seal design crank shaft with 6 bolt flange
  • 153 tooth and 168 tooth ring gears- many of the factory bellhousings will only accept the 157 tooth size, typically the aftermarket bellhousings will accept both sizes.  In many cases if you’re changing from one size to the other you will also need a new starter that is paired for that ring gear
  • Engines will be either internally or externally balanced with the external balance being most common

The GM (Chevrolet) Big Blocks

  • The early 454c.i. design used a 2pc rear main seal and had its own specific balance
  • The later (after 1990 or Gen V) 454/502 c.i. engines were all 1 pc rear main seal and externally balanced
  • All other big block displacements used a 2pc rear main seal, internal or “0” balance, and 168 tooth ring gear.  They will accept the same flywheel/flex plate as the early small block engine

LS/LT series engines 1997-present (Gen 3, 4, & 5)

  • All engines use a 168 tooth ring gear
  • All engines are internally balanced
  • LS1,2,3,6,7  have 6 bolt crank flange bolt pattern
  • LSA, LSX (aftermarket), and the new LT1 & LT4 engines have 8 bolt crank flange pattern
  • LS9 use a special 9 bolt crank flange pattern
  • Early 4.8L & 6.0L LS engines have an extended crank flange that requires a specific flywheel/flex plate

The second engine group to go over is the Ford produced V8s. This is where you have to be very careful of engine balance since Ford used three different balances. Many aftermarket stroker kits will carry their own balance that is different from the original.

Ford Small Block Engines

  • Use either 157 tooth or 164 tooth ring gear
  • 221ci 1962–1963 28.2 oz-in
  • 255ci 1979–1982 50 oz-in
  • 260ci 1962–1964 28.2 oz-in
  • 289ci 1963–1968 28.2 oz-in
  • 302ci 1968–1980 28.2 oz-in
  • Boss 302ci 1969-1970 28.2 oz-in
  • 302ci 1981–2001 50 oz-in
  • 351W (Windsor)1969–1997 28.2 oz-in
  • 351C (Cleveland)1970–1974 28.2 oz-in
  • Use a 6 bolt crank flange

Ford FE & Y Block engines 

  • FE blocks were built from 1958-1976
  • Unique crank flange bolt pattern and balance
  • 184 tooth ring gear

Ford Big Block Engines

  • Came in displacements of 370, 429, & 460c.i.
  • Also referred to as the 385 series of engines sold between 1968 – 1997
  • Uses a 176 tooth ring gear
  • All are internally balanced

Ford Modular & Coyote Engines

  • Built from 1990-present
  • Check for 6 or 8 bolt crank flange
  • Will be 4.6L, 5.0L, 5.4L common displacements
  • There was one variation for the Mustang Shelby GT500  at 5.8Lthat will be different than the others
  • all are internally balanced
  • 164 tooth ring gear

The Chrysler/Dodge/Mopar engine groups aren’t as varied, but will each need to be checked for their individual set up.

Mopar Small /Big Block and Early Gen1&2 Hemi Engines

  • Check for 6 or 8 bolt crank flange
  • 130 tooth ring gear for most, some bigger displacements may use 143 tooth
  • Will need to check for internal or external balance
  • Engines mated to automatics from the factory are not machined for a standard Mopar pilot bushing, will require special bronze bushing to run manual transmission.

Mopar Gen 3 Hemi

  • This covers the 5.7, 6.1 , & 6.4L engines
  • Will have an 8 bolt crank flange
  • Internally balanced
  • 130 tooth ring gear
  • Caution: some engines have a flush ring gear mount and others are offset by .850” from the factory.  If incorrect set up is used the starter will not engage properly

Flywheels and Flexplates For Hot Rod Transmissions

If you have more questions about the state of your engine rebuild or which flexplates and flywheels you need, don’t hesitate to check out our site or reach out to our experts! Here at Bowler Performance, we can help you identify and achieve the next steps of your hot rod transmission dreams. Contact us today!

Sours: https://www.bowlertransmissions.com/how-to-find-the-right-flywheel-and-flexplate-for-your-engine/
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