Jim Smart
November 1, 2016

Fox-Body Mustangs haven’t been this popular since the 1990s. Sales of these lightweight, good-looking 1979-1993 Stangs haven’t been this brisk in ages. They’re plentiful and cheap, and you can have yours now for a song.

The Fox Mustang with five-speed manual transmission was factory fitted with a cable clutch release mechanism, which is surely better than the original, classic 1965-1973 Mustangs with that bellcrank equalizer bar and fierce pedal effort, which has caused many an arthritic knee for more than half a century.

If you have been thinking about a five- or six-speed driveline conversion for your classic or late-model performance ride, chances are good that Modern Driveline has thought about it too. Modern Driveline has developed a wide variety of five- and six-speed conversion packages, cable clutch improvement kits, and light-pedal-effort hydraulic clutch packages for all kinds of popular performance cars. That said, what about your Fox-body driveline conversion or perhaps a hydraulic clutch for ease of pedal effort?

The Fox hydraulic clutch conversion kit by Modern Driveline is engineered for ease of installation. The clutch master cylinder secures to the firewall via this billet aluminum adaptor. Pedal to master cylinder linkage employs extraordinary “light pedal” geometry that eases pedal effort.

Modern Driveline has invested an enormous amount of time developing the new 1979-1993 Fox Mustang hydraulic clutch kit as a complement to the company’s T-56 Magnum six-speed, heavy-duty TKO, and original T-5 five-speed for the Fox. During development, Modern Driveline found variations in Fox Mustang firewall stampings and pedal support structures, which made it necessary to revise this low pedal-effort hydraulic clutch system to where it would be easy and enjoyable to use in all Fox Mustang applications. “The challenge was formidable,” says Bruce Couture of Modern Driveline. “We want challenges here at Modern Driveline, not in your garage.”

Modern Driveline introduces the Fox hydraulic clutch system for one of the most popular Mustangs in history. This system works well with both external and internal clutch slave cylinders. Both are available from Modern Driveline. We are going to show you how easy this system is to install, then invite you to take it for a test drive for the easiest clutch modulation and shifting of your life.

Modern Driveline’s Fox Mustang hydraulic clutch development has been performed on two Mustang engineering mules, hence the two colors visible in this installation. Count on excellent fit and minimal adjustment when it is time to tackle your Fox Mustang hydraulic clutch project. If you have any questions, Modern Driveline’s world-class tech support team is there to serve you.

Safety must always be your priority working in the garage. Always support your vehicle at the framerails with heavy-duty 2- or 3-ton capacity jackstands, and never with a hydraulic or scissor jack. Never trust your life to those stamped steel tubular jackstands, which can fold and collapse. Check vehicle and jackstand security before going underneath your Mustang. Always wear ANSI-approved safety glasses or a face shield. Wear proper gloves to protect your skin from hot surfaces and corrosive liquids.

Before getting started on your Fox hydraulic clutch conversion from Modern Driveline, disconnect the battery’s negative cable. Because Modern Driveline has paid close attention to detail developing this kit for easy installation, most of what you’re about to do can be done by feel and can be accessed from just above the accelerator pedal. You don’t have to remove the steering column or pedal support.


Tools for the Job

You’re going to need the following:

• Electric drill, 3/8-inch
• Drill bit, 5/16-inch
• SAE Allen wrench set
• Open end/box end wrenches; 1/2-inch, 10mm, 12mm, 13mm
• Socket wrench, 1/1-inch
• Drive ratchet, 3/8-inch
• Vise grips
• Flat-blade screwdriver, common small size
• Silicone RTV sealer
• Loctite
• A reliable friend


1. Once you have disconnected the battery, remove the driver’s seat for easier underdash access. Remember, electrical connections in a number of Fox Mustang applications must be disconnected. You don’t have to remove the seat, but it makes installation a lot easier.

2. The factory clutch cable is disconnected at the bracket and framerail as shown.

3. This is where the clutch cable passes through the firewall above the accelerator pedal. Remove the clutch cable firewall mount by removing the hex-head sheetmetal screw with an 8mm socket. Inside insulation will have to be trimmed and body sealant removed in this area to make way for your Modern Driveline clutch master cylinder linkage.

4. Remove the clutch fork dust cover. Have a buddy lift the clutch pedal to relieve tension on the cable here at the bellhousing and clutch fork. If cable release proves difficult, you can bear forward against the fork to relieve tension.

5. Disconnect the clutch cable assembly from the bellhousing as shown by removing the C-clip.

6. This is the unattached clutch cable end, which has been removed from the bellhousing.

7. This is the clutch pedal safety switch, which prevents engine start unless the clutch pedal is depressed. This switch must remain installed and be functional. Do not bypass this switch.

8. This is the self-adjusting factory clutch cable quadrant. Shown here are three components: the cable quadrant and the self-adjustor (black arrows), and the CPP, or clutch pedal position, switch (white arrow). The switch also disengages cruise control on five-speed Mustangs when the clutch pedal is depressed. The CPP switch is mandatory and must remain operational for your safety.

9. Using a pair of pliers, remove the clutch cable quadrant retaining clip and place the tip of a flat-blade screwdriver underneath the plastic quadrant for removal. It will come off easily.

10. Using a long thin flat-blade screwdriver, pry the self-adjustor spring from the pedal support. You can cut this nylon gear through the firewall from the engine compartment.

11. Now is the best time to replace clutch and brake pedal pivot bushings, which are available from Modern Driveline. Lube these plastic bushings and the shaft with white grease.

12. Preassembled Modern Driveline inside clutch pedal linkage is positioned behind the firewall. Here is the initial push lever position as it should look.

13. Using the Modern Driveline clutch master cylinder billet mount as a template, drill the three existing holes out to 5/16 inch. Add the fourth hole, also using a 5/16-inch bit. You can take these holes out to 11/32 inch for easier installation. A Unibit may also be used to get hole sizing exactly where you want it. Take care not to drill these holes too large. 14. This is what your firewall should look like once all four holes and the center register opening (former clutch cable pass-through) are set up.

15. Apply silicone sealer to the engine side of the firewall, and install the four provided Allen-head screws from the engine side. Secure inner and outer billet firewall plates. Plates must be registered on the unaltered clutch cable pass-through hole in the firewall. Plates must be centered directly on this hole or failure could result. Remove any excess sealant. The clutch master cylinder clevis is visible through the baseplate.

16. Behind the firewall above the accelerator pedal your Modern Driveline clutch linkage should look like this. The linkage endlink is tied to the clutch master cylinder on the engine side of the firewall. Continue pushing up on linkage until the plate falls into place.

17. The clutch pedal plate is fitted with setscrews, which are preinstalled until they nearly protrude into hole. This will save you time under the dash and make installation easier. Position the plate with the threaded hole down, and loosely position it on pedal pins. Raise the clutch pedal and attach the lower hole in the push lever to the threaded hole in the clutch pedal plate using the 3/8-inch shoulder bolt. Leave just enough room to use the Allen wrench on the shoulder bolt. Do not push the lever all the way down on the clutch pedal pins or preloading will occur. Use Loctite thread locker on setscrew threads, and tighten. The foremost end of the clutch lever must not interfere with the push lever.

18. Align the clutch release plate to where it is parallel with the inner edge of the clevis at the firewall plate. Push the clutch pedal all the way down to tighten the rear setscrew, then all the way up to tighten the forward setscrew. The push lever must be as straight as possible. Each vehicle is slightly different, so expect differences in pin and linkage adjustment.

19. With the clutch pedal in the up position, tighten the forward setscrew.

20. The clutch master cylinder is tied to the preassembled underdash linkage via this threaded rod and clevis, which are adjusted to position the master cylinder and baseplate exactly 1.400 inches apart. Once you have achieved this dimension, lock down the nuts.

21. Here is the adjusted clutch master cylinder to clevis connection behind the firewall.

22. Clutch master cylinder studs are installed and secured. Our integral reservoir clutch master cylinder clears the toughest of applications, including a Cobra power brake booster.

23. The Fox hydraulic clutch system by Modern Driveline is compatible with any of the company’s slave cylinder package. This is the internal slave/release bearing, which is compatible with nearly every Modern Driveline manual transmission. The internal clutch slave/release bearing is optimal for tight installations, where space is at a premium. This particular 1988 Mustang GT is fitted with the Tremec T-56 Magnum six-speed.

24. This is Modern Driveline’s LF Series external hydraulic clutch slave cylinder, which bolts onto your cable-style small-block bellhousing with minimal modifications. The clutch fork becomes a pusher instead of the cable pull style. All you have to do is install and bleed the slave cylinder, then adjust the clutch.