For most Replica builders and owners, when it comes to the clutch system, there are very few choices. Even more restricted are the cars that use donor parts from a Fox or SN95 Mustang, most popularly the Factory Five Roadsters, which use the standard cable-operated clutch. Good news! We've found a hybrid that combines the easy effort and linear action of a hydraulic system with the simplicity and availability of a Mustang-based system. Read on, we'll give you the details.
The subject of this story is a Factory Five Replica Cobra, MKII vintage, well known in the North East area as a dual-purpose car-it's both street driven and used for club racing events. This car has racked up over 4,000 miles per year in street miles, as well as many hard miles being thrashed on such tracks as VIR, Watkins Glen, Pocono, and others. The driveline is actually quite ordinary, all taken from a 1988 Mustang GT, left stock, but converted to a carburetor for fuel/air delivery. The chassis is the three-link version, along with upgraded brakes, suspension, and safety items, but otherwise a basic car.
During the construction of the car, a clutch system idea was planted while driving every day in the owner's truck that had a hydraulic clutch with buttery smooth action. A survey on the FFR forum's website (www.ffcobra.com) showed that the only available alternative to the cable operation was the Wilwood setup. This is a great system that allows for easy brake balancing, but was too costly for our owner. Also, since the owner is an engineer with access to a machine shop, he reasoned he could make his own system.
The first order of business was to see if a system could be assembled from readily available parts, be made to work with the FOX Mustang pedal assembly, and fit within the Cobra's footbox-no simple task. The first step was to see what slave cylinders/systems were available for the T-5 five-speed transmission and stock bellhouse. Very quickly, the system sold by JMC Motorsports was found to fit the needs, as it's complete with all brackets, hardware, and instructions for an easy installation. Once this system was decided on, the next task was to match a master cylinder up at the pedals. A critical aspect of this step is to properly size the bore of each cylinder to assure correct operation. After much research and questioning, a 3/4-inch inside diameter master cylinder was selected from CNC Brakes. All the lines and fittings were found in a kit from Longacre Racing Products. We had to figure out how to make it work while keeping the system hidden, mostly to have the engine compartment uncluttered.
To actuate the master cylinder, there were two basic choices: either push forward with the pedal, or make a new quadrant to push the master cylinder. Here's where the engineering paid off, as a CAD system was extensively used to replicate the Mustang pedals and travel, pivot points and rotation, as well as the stroke of the master cylinder and where to exactly place all the parts for best operation. After looking at many ideas, a plan was formed to make a replacement quadrant that pushed toward the driver. This way, the master cylinder could be located directly above the pedals, and all could be hidden under the aluminum panels.
A quadrant was developed that fit the Mustang pedal, and that had many locating holes for installing the master cylinder clevis pin. In addition, the master cylinder's main shaft is threaded, so the system can be tuned. These two methods of adjustability came in very handy, as we needed to make sure the cylinder had full travel, but also fully returned so the system could draw fluid from the reservoir. Also, we wanted to keep the Mustang's pedal stop in use, and not bottom out the master cylinder during hard shifts. Initially, a reservoir was attached to the master cylinder, but the final design included a remote reservoir outside of the pedal box, so the fluid level could be easily checked. A few prototypes were built, each one beefier than the last, so the system would be solid under hard use planned for weekend club racing. The final master cylinder mount is a two-piece design, which securely locates the m/c, but also allows it to be pivoted for best alignment to the quadrant. A hard line extends from the master cylinder to halfway down the footbox, where it joins a flexible line that feeds the slave cylinder, isolating the parts from any vibration or motor movement.
The system worked as planned after extensive bleeding, adjusting, and experimenting. We checked the travel of the clutch fork in the hydraulic system, compared it to a cable system, and found both systems operated the same. Even with a heavy-duty clutch, in our case the Ford Motorsports King Cobra clutch, pedal effort is easier than many new cars, engagement is halfway through the swing, is quite linear, and very driver-responsive.
Driving this system is a joy. Many who have driven the car talk about clutch effort when compared to their own Cobras and have repeated this sentiment. Traffic lights are no longer an exercise in leg cramps, and shifting quickly is also effortless. As intended, four months after hitting the road, this car started seeing action at the racetrack. While there were initial problems with other systems in the car, the clutch never faltered once and engages smoothly even in sweltering summer track conditions all day long.
Unfortunately, a year later, the car was involved in a wreck at Watkins Glen. So the car was fully disassembled for repairs. The trans and clutch were removed to fix a leaking rear main seal. We were delighted to find a near-perfect clutch assembly after over a year of hard racing and spirited street driving. It has since been re-assembled without any changes, and was bled and ready for use quickly.
This is the great concept of these replicas. There is no correct way to build them, and each owner can be as creative as money, ability, and ingenuity allows.
