A clutch is one of the crucial items within the drivetrain sector. A clutch is responsible for moving the power from the engine, to the drivetrain itself. There are many different types of clutches, varying from material to actual designs. However, the common theme is a clutch cannot have any slip. If a clutch slips, power is not fully transmitted to the wheels of the car. As a result, power loss occurs and the drivetrain is not optimized. Upgrading a clutch, along with a clutch line (if hydraulic), throwout bearing, pressure plate, and pilot bearing can really reduce parasitic loss and have better transmission of power towards the wheels. One additional component that coincides with the clutch is the flywheel, but mor eon that later.

Choosing the correct aftermarket Mustang clutch means taking into consideration several operational features, including clutch feel, operating temperature range, wear characteristics/durability, clamping force, the break-in period, and the clutch material.

There are a lot of people who believe if you choose a clutch made of extremely aggressive material, it will be better for your Mustang, no matter what situation you drive in. This is not true. Choosing a clutch that is too aggressive for the driving you do means compromising on some of the above features.

If you drive a car with a manual transmission, you know what to do to move the car: press the clutch, select a gear, and release the clutch while pressing down on the gas. Because the engine is constantly turning and your wheels are not, the clutch also allows you to disconnect the wheels from the engine without killing it. Pretty simple, right? But, what’s happening to your car when you do that? The clutch connects two rotating shafts so that they can either be locked together to spin at the same speed, or detached to spin at different speeds. These actions provide the two basic functions of your Mustang’s clutch:

1. To gradually apply engine power when the car is moving

2. To interrupt power to avoid gear crunching when shifting, or stalling out when stopping

When you’re driving, this engages the clutch and allows power to transfer from the engine to the transmission and wheels. When the clutch is disengaged (while shifting), the power transfer stops, and the engine continues to turn without force to the wheels. To fully understand how a clutch works, however, you need to know all of the parts of the clutch system, and how they work together.​

There’s more to the clutch than just the disc and the pressure plate. There are actually seven different parts to the system that you should know about.

• Engine: generates the power needed to move your Mustang
• Flywheel: bolts to the engine crankshaft and provides a friction surface for the clutch
• Clutch Disc: a friction surface that transfers power from the engine to the transmission
• Pressure Plate: provides the clamping power needed to lock the clutch to the flywheel
• Throwout Bearing: sometimes called the release bearing, this part reduces the friction between the clutch fork and the springs in the pressure plate
• Clutch Fork: provides a lever action to engage or detach the clutch
• Transmission: provides a lot of selectable gear ratios, which allows the driver to match the power the engine puts out to changing driving conditions

Let’s take a look at each of these parts a little more closely, so you know just how to optimize your Mustang's clutch system.

You already know the engine runs the car. The backbone of the engine is the crankshaft, and it is the hardest working part of your engine. The crankshaft drives all belt-driven accessories, such as the water pump, the alternator, the A/C, and the fan.

However, its primary function is to change the give-and-return motion of the piston and rod into a circling motion that is transferred to the transmission and drive wheels. As the fuel/air mixture in the cylinder burns, it forces the pistons down. Each piston is connected to the crankshaft by a connecting rod.

As the piston goes down, the connecting rod causes the crankshaft to turn. This isn’t a big deal if your car is a daily driver that you never race. For highly modified cars putting out extreme amounts of power, this task can be hard on the engine.

The flywheel does a lot of things – it maintains engine momentum, reduces vibrations caused by cylinders firing, and it provides a smooth friction surface for the clutch. The flywheel’s main function is to transfer engine torque (the turning effort produced by the pressure from the crankshaft on the pistons) from the engine to the transmission.

The flywheel connects the clutch and the driveline to the engine. One side is bolted directly to the crankshaft, and one side is bolted to the clutch assembly. When the clutch is engaged, power transfers from the engine to the wheels, through the flywheel itself.

The flywheel's rotation creates forces that can cause power loss if the flywheel is too heavy. One modification commonly used to reduce the loss is to convert to an aluminum flywheel. Compared to traditional steel flywheels, aluminum flywheels weigh substantially less than the steel counterparts, which can drastically improve efficiency. The flywheel/clutch/transmission combination then directs the power to the driveshaft.

The pressure plate is a spring-loaded clamp that is bolted to the flywheel. As you can tell by the name, the pressure plate presses the clutch disc and allows for the transfer of power to the transmission.

When the clutch pedal is pressed down, the throw-out bearing – also called the release bearing – moves toward the flywheel. It pushes in against the pressure plate’s release fingers and moves them against the force of the plate’s springs. This action moves the pressure plate away from the clutch disc, interrupting the flow of power and reducing friction.

The clutch fork provides a lever action to engage or disengage the clutch. It forces the throw-out bearing into the pressure plate.

TIP: Every clutch, regardless of type, has a break-in period. This means you need to be careful not to overheat the clutch from excessive slipping. Always follow the suggested break-in guidelines, or risk clutch failure.

Before you buy a clutch, you need to ask two questions to understand the characteristics of your Mustang:

• How much power does your Mustang make?
• How is it used? (street driving or track use, or a combination of both)

You’re also going to want to know which type of disc you will need – puck-style or full disc? Should I get one with or without a torsion dampener? And what material should the clutch disc be made of? Should you go with a compound or Kevlar, or a Carbon-Kevlar mix? What type of flywheel should you get: steel or aluminum? The amount of information out there can be dizzying, but we’re here to make sense of it for you.

There are two types of clutch discs – full discs and puck-style.

Full Disc: You will find OEM replacements and aftermarket Mustang clutches designed with stock applications in mind, usually have full disc clutches.

Puck-Style Discs: These discs – available in multiple puck configurations – cool better than full discs. This style of disc is usually found in clutches meant for racing applications.

A twin disc clutch, while generally more costly, is much more beneficial than a traditional single disc clutch. Compared to single discs, twin clutches get rid of heat better. They also have a higher hp tolerance and provide smoother shifts. Twin disc clutches provide more friction material, which in turn can result in quicker engagements. The primary benefit is while essentially doubling the clamping surface, the pressure on the pedal remains light and simple.

Clutch with a Torsion Dampener: Also called the sprung hub disc, the hub floats in a spring loaded assembly which is attached to the carrier plate – the circular metal plate that holds the friction material. When the hub is loaded – when the clutch is engaged – the springs help absorb the load, rather than transfer it directly to the carrier plate. This keeps the shock of aggressive engagement from damaging the drivetrain.

Clutch without a Torsion Dampener: In this case, the hub is connected directly to the disc carrier plate.

There are many different types of material used on clutches. It would be impossible to go into detail about all of them, so let’s just talk about the most common ones.

Organic: Organic means the clutch disc is made of a blend of several different materials. The disc is generally steel-backed, and the material includes metal fibers that are woven into a multi-compound material. Most stock clutches are made of organic material such as fiberglass, which is similar to a brake pad.

Clutches made of organic material are generally very similar to the OEM clutch, and are known for smooth engagement, long life, broad operating temperature, and a very quick break-in period. An organic clutch will stand up to hard use, but it won’t be able to take repeated abuse because it will overheat.

Carbon-Kevlar Mix: The materials in these discs are segmented together to make a very friendly material for your Mustang. A disc made of this material has a similar feel to stock.

Kevlar: Kevlar is a highly durable material that is more resistant to hard use. It has similar engagement to discs made of organic material, but it may glaze slightly in stop-and-go traffic. However, with Kevlar once you’ve broken in the disc, if it glazes over it doesn’t stay that way. It can overheat and will go back to its original state once it has cooled down. This doesn’t mean you can completely cook the clutch and have it still be okay though. If you “cook” your clutch, the disc will not return to its original form.

Hybrid Carbon/Ceramic/Organic: These discs have organic material on one side and a segmented carbon or ceramic material on the other. The idea behind these is the organic side will help smooth the engagement and reduce the shuddering from the segmented side. However, they can be used in the same situations as regular organic clutches, though the carbon or ceramic side will wear the flywheel and pressure plate surface faster in traffic situations.

Carbon: Carbon is a material that can withstand a lot of heat. However, clutch engagement is more abrupt, and the flywheel surface will wear faster, especially in traffic situations. Still, carbon is more flywheel-friendly and slightly more durable than ceramic.

Ceramic: Like carbon, ceramic discs can also withstand a great deal of heat – more than carbon. Ceramic discs will cause the flywheel to wear faster, and puck-style discs with ceramic can result in slight shuddering when used in stop-and-go traffic situations. Since ceramic is a more aggressive material, it will hold more power.

Sintered Iron: This is the type of material you want your clutch to have if your Mustang is strictly a racing car. Clutch discs made of sintered iron can withstand very high temperatures, and will accommodate more that 700 hp. Engagement is immediate on or off, and a clutch disc made of this material will require a special flywheel surface.

A sintered iron disc is primarily used in high-horsepower, endurance racing applications. If you run quarter-miles only, then this is not the clutch for you. Clutches like these do not work as well when the weather is cold, and a high-durability flywheel surface is required. If you use a standard flywheel with a clutch disc like this, be prepared to change it out after every race.

It is worth repeating that picking out the right clutch for your Mustang is a difficult process that ultimately takes a good bit of research. There is really no definitive power range you can assign to one type of clutch, yet at the same time, it's not going to make a whole lot of sense to use a sintered iron clutch in a sub-500 HP Mustang. When purchasing a clutch, take into consideration everything you plan on doing with the car and use the above chart as a reference tool to help make your decision a more confident one.

While browsing for a new clutch, you may notice that many, if not most, aftermarket manufacturers use a “stage” system (stage 1, stage 2, stage 2 , for example) to rate their clutches performance. Typically, the lower the stage number, the more similar the aftermarket unit is to the stock unit.

It is important to note, however, that there is no industry standard definition in regards to clutch stage level or series number. This means that a stage 2 clutch from company A could be entirely different than what company B has labeled their stage 2 clutch.

Thus, it is important to read all of the finer details when looking at clutches, as the ‘stage’ names are a marketing term, not a regulated term. Read below to get a better understanding of what each typically stage offers.​

Determining which clutch is right for you depends upon how much power your Mustang is making at the time of install. Some manufacturers, like SPEC, rate their clutches based on torque ratings. Other companies, like RAM, rate them based on horsepower at the crank. When choosing a clutch you should always select the clutch that fits your needs based on these numbers. Keep in mind that the higher stage the clutch is, the firmer it will be.

At the risk of being repetitive, DO NOT BUY MORE CLUTCH THAN YOU NEED. If you have a mildly modified Mustang, you don’t want to purchase a clutch that is meant for a racing application, and vice versa. Putting a clutch meant for street driving on a Mustang built for racing means that it will not last as long as you may need it to.

A simple organic disc will handle a wide variety of uses, including street driving and racing. A Kevlar disc is a good choice for a Mustang that races heavily on the track or the road, especially if you have forced induction. Carbon and ceramic discs should be left to high-horsepower Mustangs that see lots of drag racing, or are only track/drag cars. And sintered iron should only be used on high-horsepower, endurance racing Mustangs.

Stage 1: Clutches dubbed as stage 1 are the first level above a stock clutch. Typically, they have a higher clamp load and are usually good for an extra 100 ft-lbs of torque over stock discs. Furthermore, stage 1 clutch kits still utilize a full-disc, organic compound friction surface making them very streetable.

However, because of the softer friction surface, like the stock unit, they will not last long under heavy racing conditions. These kits sell anywhere from $280-$360 depending on manufacturer and engine combination.

Stage 2: Stage 2 Clutch kitw will be capable of holding more power over their stage 1 brethren, but will also be more aggressive in terms of operation. However, as noted above, there is no industry standard in regards to clutch kit naming.

This becomes very evident when looking at stage 2 and comparable clutch kits, and thus makes it doubly important to read each kit’s details very carefully. We saw with stage 1 kits, the friction surfaces were only organic compounds.

Stage 2 kits, on the other hand, vary with manufacturer. Some stage 2 kits will still be an organic compound (still more aggressive than stage 1 compounds), whereas others may utilize Kevlar, or a mix of organic and metallic materials.

The latter materials, Kevlar and semi-metallic, will offer more aggressive engagement and bite, and will stand up better to hard driving. Withstanding 600 ft-lbs of torque seems to be the industry norm for these mid -level upgrade kits. Some stage 2 offerings may be puck-style, as opposed to full-disc. We will touch on this subject further on. Prices are around $400.

Stage 3: If you’re mainly interested in racing and pushing the limits of your Mustang every time, all the time, a stage 3 kit is probably what you are looking for. Some stage 3 kits are still made with organic compounds, but the majority uses a more aggressive semi-metallic carbon or semi-ceramic friction surface, which offer the most bite and near instant engagement.

Stage 3 discs are made to work in the neighborhood of 700 ft-lbs of torque, and their aggressive and instant engagement nature make them more suitable for track use over street use.

However, many manufacturers claim that their stage 3 clutch will still work well on the street, but it is not uncommon to have clutch chatter at low RPMs whilst cruising the town. Available in full-disc or puck-disc, stage 3 units cost anywhere from $360-$550.

Having more clutch gripping power is always better than not having enough. If you plan on making additional modifications in the near future, but are in need of a clutch now, it is better to go with a stronger clutch that will handle your future mods.

When replacing a clutch, you should ALWAYS either resurface your flywheel or replace it with a new one for the following reasons:

• Prevents installation of a warped flywheel
• Creates a better gripping surface for the clutch
• A new clutch and a new flywheel will match the performance of your Mustang’s power
• Along the same lines as the gears, it can be costly to install a new clutch. Installing a new flywheel will ensure that you only have to pay the shop once.

The typical break in period for a clutch is about 500 miles of mixed highway and city driving. It is recommended to take it easy on the new clutch until the break in period is over to avoid any potential damage. Allowing the clutch to break in will ensure that the clutch and flywheel seat together properly and you will get the best performance out of the combination.

When installing an upgraded, aftermarket clutch, the normal clutch engagement point will no longer be applicable. Adding a clutch adjustment kit will allow you to adjust the tension on the clutch cable so that you are able to engage your clutch properly.

Stock flywheel was generally composed of friction material. Friction material is known as "paper, elastomerics, graphics, and sintered metals. A wide variety of other materials are also used, such as ceramics, advanced fibers and different metal alloys." However, on 2003/2004 Cobra models, an aluminum flywheel was utilized in the stock setup.

A slave cylinder is similiar to a master cylinder in that it stores hydraulic, uncompressible fluid. This is primarily utilized for hydraulic clutch setups. A hydraulic clutch setup generally has less pedal pressure than a traditional mechanical assembly, but still utilizes a traditional throwout bearing.

Bench bleeding is a key part of a throwout bearing (slave cylinder) installation for any hydraulic clutch driven vehicle. Failure to complete this process will result in air in the hydraulic clutch system. Air in the system will result in the inability to shift into gear as well as some strange noises. 

Step 1: Using a very clean container pour the OEM specific fluid in (roughly 4oz).

Step 2: Submerge the feed hose to the slave cylinder into the brake fluid ensuring the line cannot intake any air.

Step 3: Slowly compress the bearing down, releasing the air inside of the slave cylinder until the bearing is fully compressed. Make sure the inlet hose stays fully submerged during this process (Bubbles will rise from the submerged hose to let you know you are doing it correctly).

Step 4: Slowly release the bearing back up, allowing the fluid to be drawn into the hydraulic cylinder. Make sure the inlet hose stays fully submerged during this process  (If the hose comes out of the fluid for a split second then air will be sucked into the cylinder).

Step 5: Repeat process 3 and 4 until you don't see air coming out of the feed hose (bubbles). This may take several compressions to achieve. Vacuum force will hold the fluid into the hydraulic cylinder, but it is essential to cap the feed line with the original cap to ensure no foreign debris enters the hydraulic cylinder.

Step 6: Once the slave cylinder is installed into the bell housing and the transmission is on the transmission jack, you will need to remove the cap and either wrap the feed line with a clean rag or connect the master cylinder line as some fluid will compress out when the transmission is bolted to the engine block.

Step 7: Bleed the hydraulic assembly according to the factory service manual procedure.

Stiffness of a pedal can be from a multitude of different variables. Some common variables can be the type of clutch, the material the clutch is made with, whether the clutch is properly bled, etc. On 2005 models, the clutch is engaged hydraulically. As a result, improper bleeding of the line can leave air trapped which will soften the pedal pressure greatly. Other soft clutches, such as Mcleod RST and RXT, are soft by nature. While on the other hand Exedy tends to produce clutches on the stiffer side of pressure.

What clutch is best for your modified Mustang? Well that depends a lot on the driver (aka, you). For someone just looking to cruise the town with the occasional spirited drive down the strip, a stage 1 clutch will fit the bill without issue. For those drivers that are more regularly racing their Mustangs, but still wish decent street manners, a stage 2 clutch kit would be a good choice. Finally, hardcore drivers that want the power transmitted to the wheels right away, a stage 3 kit will offer you that instant engagement and high load capacity you’re looking for, allowing for many high RPM launches down the strip. The bottom line:

• Stage 1: great for street-driven Mustangs with higher than stock power levels
• Stage 2: aggressive engagement and stronger friction materials make these clutches good for a combination of street & strip driving
• Stage 3: geared for those with a heavy foot and spend lots of track at the time. Manufacturers claim streetability, but more orientated for aggressive driving and track use
• Twin Disc Cluthes: Superb performance and usability in all scenerios, but very pricy