All About Fox Body Clutches - Part 1

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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 begin looking at replacement options, let us first talk about what a clutch is and how it functions (we won’t dwell on this too long), then a briefly discuss the stock equipment, and finally on to the fun stuff – upgrades.

Fox Body Clutch Overview

Like any component on an aging Mustang, the clutch used in manual-transmission equipped Foxbody Mustangs 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.

Fox Body Clutches - Facts & Fundamentals

  • • 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 that 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

Clutchology 101: How a Fox Body 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 finally to the wheels, moving the car forward. Clutches operate on a very simple principle – friction. Clutch discs, are a disc (D’oh!) with a specially coated friction surface, called the clutch lining, (the lining varies, dependent on manufacturer, intended use, vehicle etc.) that when mated with the flywheel (the part on the engine that the clutch engages with) 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 ‘little’ bit of force…), it locks and will turn at the same pace as the engine flywheel with no slip.

Your Mustang's Original Clutch

The original clutch used in all Foxbody Mustangs (1979-1993) is a constant 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 15,000mi, 30,000mi, or even 60,000+mi, depending on how you drive. Many Foxbody Mustang owners have 100,000+miles on the odometer and are still using the stock, factory equipped clutch! Mind you, it is most likely near its end, but it goes to show that how you drive is the main factor in the longevity of your clutch.

Is my Fox Body Mustang's Clutch Toast?

How do you know when the clutch in your Mustang is going to break? The most obvious symptom that 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.

Fox Body Mustang Aftermarket Clutch

Replacement Clutch Options For Fox Body 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 probably could imagine, are the least expensive. Stock units are available from a host of manufacturers. Ford and Exedy are two reputable sources for replacement OE units.

Now, 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. To begin, performance clutches can support more horsepower and torque. How much more? Well that depends on the manufacturer, and specifically, 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 and so forth. Sometimes they may even have levels between whole numbers (ex: stage 2, stage 2+, stage 3). 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. Now, in the aftermarket world, particularly with clutches, there are a ton of players out there looking to make a sale. Between technical jargon and competitive pricing, sometimes it is quite hard to figure out which clutch will do the job and which is a lemon. Spec, Exedy, Ram and Ford Racing are four reputable companies that offer excellent performance clutches, available a la carte depending on what you need. The four companies all offer varying levels of performance and all 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 that Ford smallblock is, or will be, creating.

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, as there really are just so many options out there. On a side note, when choosing a new clutch, just be aware that some manufacturers rate their clutches by horsepower whilst others by torque. Also be aware that 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.

Now, there are a few other parts that work in conjunction with the clutch that are worth looking at and perhaps replacing/upgrading at the same time as the clutch. To read about these, please continue on to Clutches : Part II(link this). There we’ll go through cables, cable adjusters, quadrants and flywheels.

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