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All About Foxbody Clutches

Written By: Connor MC

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A quality clutch can transform your Mustang from a mundane, run of the mill muscle car into a tuned performance car you feel connected with. For that perfect clutch feel, ditch the stock clutch and find the performance level the rest of your Mustang was designed for.

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Before we look at stock or aftermarket replacement options for your Foxbody Mustang's clutch, let's first talk about what a clutch is, how it functions, and other stock equipment. Finally on to the fun stuff – upgrades.

Foxbody Clutches - Facts & Fundamentals 

Like any component on an aging Mustang, the clutch used in a manual transmission Foxbody Mustang will eventually need to be replaced. At what interval and after how many miles depends on how you drive. If you’re driving your Mustang all the time, dropping the clutch and spinning the tires to boot, you’ll be replacing the clutch sooner rather than later. Not to say this is a bad thing - rather it is just a fact of life. Along with the clutch there are other components you'll want to consider replacing to make sure your clutch and clutch system are operating at their peak.

  • The clutch connects and transmits the power generated from the engine through the transmission
  • Stock clutches are 10.5 inches in diameter
  • The most obvious symptom a clutch needs to be replaced is the engine revving and the car not accelerating
  • When replacing a clutch, Mustang owners have two options: stick with an OE stock unit or upgrade to an aftermarket performance clutch
  • Clutch quadrants compensate for clutch cable wear as the clutch ages
  • Flywheels are the plates on the engine that connect to the clutch and transmit power to the wheels
  • Stock flywheels are made of iron and weighs 22 pounds
  • Aftermarket performance flywheels use either billet steel or aluminum and weigh much less than stock
  • Adding an aftermarket flywheel will no cause the engine to gain power, but it will rev faster because of the decreased weight
Foxbody Convertible at the Drag Strip

Clutchology 101: How a Foxbody Mustang's Clutch Works

The clutch connects and transmits the power generated from the engine through the transmission, where it then goes through the differential, and then finally to the wheels to move the car forward. Clutches operate on a very simple principle – friction. Clutch discs are a disc with a specially coated friction surface called the clutch lining (the lining varies dependent on manufacturer, intended use, vehicle, etc.). When mated with the flywheel (the part on the engine the clutch engages with) the lining will provide an iron, non-slip grip. Basically, the clutch’s surface is so ‘sticky’ that when pushed up against the flywheel (this does take a bit of force) it locks in and will turn at the same pace as the engine flywheel with no slip.

Spec Billet Steel 50oz Flywheel for 1986-1995 5.0L and 1993-1995 Cobra Mustangs
Billet Steel 50oz Flywheel for 1986-1993 5.0L and the 1993 Cobra Foxbodies

Your Mustang's Original Clutch

The original clutch used in all Foxbody Mustangs is a 10.5 inch in diameter, 10 spline clutch (clutch lining varied, however). The stock clutch is perfectly adequate for an OE car, albeit a bit heavy. Engaging and disengaging the clutch on 1987-1993 model Mustangs is equivalent to lifting a 39 pound weight! Who said you need to go to the gym to get fit. And again, the life of the clutch is dependent on your driving style. It could last 15,000 miles, 30,000 miles, or even 60,000 miles. Many Foxbody Mustang owners have 100,000 miles on the odometer and are still using the stock, factory equipped clutch! Mind you it's most likely near its end, but it goes to show how you drive is the main factor in the longevity of your clutch.

Convertible Foxbody Mustang Cruising Down the Road

Is My Foxbody Mustang's Clutch Toast?

How do you know when the clutch in your Mustang is going to break? The most obvious symptom the clutch is slipping is of course the engine revving and the car not accelerating. Other indications are changes in clutch engagement point (a clutch suddenly engaging higher off the floor is wearing). If you are experiencing any of these symptoms, or just decide your clutch has had enough enough, there are plenty of options out there for you.

Replacement Clutch Options For Foxbody Mustangs

When replacing the clutch there are two avenues to choose from. Stick with an OE stock unit, or upgrade for an aftermarket performance clutch. If you plan to keep your car stock, there really is no need to upgrade to a performance clutch. Stock clutches, as you can imagine, are the least expensive. Stock units are available from a host of manufacturers. Ford, Exedy, and SR Performance are three reputable sources for replacement OE units.


SR Performance OE-Style Replacement Clutch Kit for 1979-1985 5.0L Foxbodies
OE-Style Clutch Kit for 1979-1985 5.0L Foxbodies

If you plan on upgrading your ride (or already have) and are looking for a bit more ‘bite’, then consider an aftermarket performance clutch. Differences over stock clutches are many. Performance clutches can support more horsepower and torque. How much more? Well that depends on the manufacturer and the clutch. Manufacturers commonly market performance clutches in stages, or by numbers (100, 200, 300 etc). I.E., the next level up from a stock unit is a stage 1 clutch; an upgrade from stage 1 is stage 2 and so on.

Generally speaking, the difference between levels is the clutch lining material and spring/diaphragm force. As you move up clutch levels, horsepower and torque ratings increase as does clutch stiffness during operation. Spec, Exedy, Ram, Ford Performance, McLeod, Centerforce are six reputable companies who offer excellent performance clutches. Most companies offer varying levels of performance and usually include a release (throwout) bearing and alignment tool as part of the package (very important for install). Which level to choose depends on what kind of horsepower your engine has, or will be, creating.

Spec Stage 2 Clutch Kit for 1986 to Mid-2001 GT and 1993-1998 Cobra Mustangs
Stage 2 Clutch Kit for 1986-1993 GTs and the 1993 Cobra

Additional Things to Note on Mustang Clutches

Outlined above is what I like to call Clutchology 101. Nothing too complicated, but it should provide some insight into the world of Mustang clutches, since there are just so many options out there. On a side note, when choosing a new clutch, be aware some manufacturers rate their clutches by horsepower whilst others by torque. Also be aware it is highly recommended (if not required) to change the release/throwout bearing when doing a clutch swap. Most clutch kits take this into account and include one, but not all do. Furthermore, when replacing a clutch, the flywheel must always be resurfaced (for those guys undertaking the swap themselves) or replaced.

There are a few other parts working in conjunction with the clutch worth looking at and perhaps replacing/upgrading at the same time as the clutch. Those will be detailed below. Consider the next section "Part 2" of our clutch overview.

RAM HDX Clutch for 1986 to Mid--2001 GT and 1993-1998 Cobra Mustangs
Underside of the Clutch Disc (right)

Clutch Cables - How Do They Work?

The clutch cable works exactly like brake cables do on your bike. Pull the brake lever and the brake engages. Release the lever and the brake releases. In the automotive world of mechanical clutches the same principle applies – except opposite motion. Pushing the clutch pedal causes the cable to disengage the clutch and releasing the pedal engages the clutch. No surprise here. Anyway after years of use, just like bike cables, automotive clutch cables can stretch, fray, and even bind in their housing leading to sloppy clutch movement. To fix this issue, simply replace the cable.

Ford Performance Clutch Cable and Fork for 1979-1993 5.0L Foxbodies
Clutch Cable and Fork for 1979-1993 5.0L Foxbodies

Replacing a Foxbody Clutch Cable: Stock or Aftermarket?

Surprisingly, many Mustang enthusiasts recommend using a stock, OE cable. They are actually quite durable. An option you may notice aftermarket companies including on their clutch cables is an adjustable option. The idea here is that if used in conjunction with a firewall adjuster (basically a screw you install in the firewall), you can adjust the cable and thus clutch engagement point from inside the car – no wrenches necessary. This is an entirely optional choice. Many people prefer this adjustable setup (the firewall adjuster is another separate piece) and many also keep the stock setup. The choice is left to you.

Adjustable SR Performance Clutch Cable Kit for 1983-1993 5.0L Foxbodies
Clutch Cable, Quadrant, and Firewall Adjuster for 1983-1993 5.0L Foxbodies

Clutch Quadrants - the Grand Adjuster

The second piece to look at is the clutch quadrant. This is a piece you don't want to replace unless you have to (meaning the one in the car is broken). Later model Foxbodies (1987-1993) came equipped with a self-adjusting mechanism incorporated into the clutch pedal. This self-adjusting system is basically a ratcheting piece built into the clutch pedal assembly to compensate for clutch cable wear as the cable ages and stretches. This system works really well.

The only issue is the stock piece is plastic, and after a lot of use they commonly strip, no longer working. You typically notice this problem when you press the pedal and hear a ratcheting noise. The stock quadrant is toast. The solution is to replace it with an aftermarket aluminum piece. The aluminum pieces are much more durable, and some are even tailored to work specifically with their own adjustable clutch cable. The issue with this part is it's a pain to replace! The whole pedal assembly and a good portion of the steering system and lower dash must come out to accomplish this.

Stock Plastic Quadrant Versus Aftermarket Aluminum Quadrant for 1979-2004 Mustangs
Stock Plastic Quadrant Versus Aftermarket Aluminum Quadrant

Flywheels - the Power Convertor

Now onto the last piece of the puzzle, the flywheel. As previously mentioned, the flywheel is the plate on the engine that connects with the clutch and transmits the power to the wheels. It was also said when replacing the clutch, the flywheel must also be replaced or machined. The main reason people replace the flywheel is if they are building a high-performance car. In most cases, the stock flywheel just needs to be resurfaced and you are good to go. If the stock one needs to be replaced you can go with a stock option, which is recommended for street applications, or aftermarket.

The difference between a stock and aftermarket flywheel is a construction material. A stock flywheel is made of iron and weighs 22 pounds. Aftermarket performance flywheels use either billet steel or aluminum and weigh considerably less (both stock and aftermarket are 157 tooth, 28 or 50oz balanced, depending on year of engine).

Ford Performance 50oz Steel Flywheel for 1981-1993 5.0L and 1993 Cobra Foxbodies
50oz Steel Flywheel Installed

Benefits of an Aftermarket Flywheel

Flywheels are kind of like differential gears in the sense they can radically change how the car performs. Swapping the stock piece with an aftermarket aluminum or steel piece won't net you any power, but the engine will rev faster due to less weight, thus helping your acceleration. With this increase in performance, however, comes a decrease in overall driveability. As a street car, you may find the revving nature of a billet flywheel to be somewhat annoying. For this reason performance flywheels are recommended for racing applications.

Remember…the cable, quadrant and flywheel are some of the necessary components to check when doing work on the clutch. At the minimum, a new clutch cable is a good idea when replacing the clutch. It's cheap insurance! One last note: if you are purchasing a new flywheel, double check you are buying the correct flywheel with the right external balancer. Different years used different weights.

RAM Billet Aluminum 28oz Flywheel for 1986-1995 5.0L Mustangs
Billet Aluminum 28oz Flywheel for 1986-1993 5.0L Foxbodies
Fitment includes: 1979, 1980, 1981, 1982, 1983, 1984, 1985, 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, GT, Cobra, LX, SVO