KJ Jones
December 19, 2013
Contributers: K.J. Jones, KJ Jones Photos By: K.J. Jones

Horse Sense: Throughout the '70s and well into the '00s and beyond, Quarter Master has long been recognized for clutch systems designed for circle-track racing. However, despite making its mark in roundy-round competition, a little known fact about the company is that it actually started out as drag-race chassis manufacturer; Quarter Master (for quarter-mile... get it?). It's all in the name!

Working with bad-dude Mustangs is our daily mission here. Be it a feature story on a hot-looking Pony, or a technical report on an innovative new part, bringing you wall-to-wall coverage about the latest and greatest is what we do.

While Mustang LXs and GTs are our typical beat, there are occasions when our spotlight shines on Shelby GT500s. These factory-supercharged, Four-Valve beasts respond well to basic bolt-ons and tuning.

Of course, GT500s are plenty awesome in bone-stock form, so the aforementioned upgrades typically are made based on owners' desire to improve their Ponies, as opposed to there being a specific need for different hardware. However, with this being said, the clutch is one component that actually needs addressing when you decide to take a Shelby's power and torque into the 700-1,000hp stratosphere, which seems the norm for modded Shelbys.

As with any stick-shifted 'Stang, the clutch makes all the difference in ensuring every bit of the engine's performance is transmitted from the engine to the rear wheels. Interestingly, Ford's latest higher-output Mustangs rely on factory-installed, Sachs twin-disc clutch units that are great at stock power levels, but can fold like a weak hand in the face of big steam. Enter Quarter Master Racing Clutches and Driveline Components (www.quartermasterusa.com) with a new twin-disc clutch option for stout street Shelbys.

The company's Optimum-SR 10.4 Two-Disc System (PN 226050190-R; $2,312.50) is lightweight clutch-and-flywheel hardware for '11-'13 GT500s that supports massive power and grunt, without sacrificing easy pedal operation or street driveability. With several basic mods already handled, Saoud Alahmad's '12 Shelby is beyond-stock stout, and a good candidate for installing and evaluating Quarter Master's first Mustang performance unit.

We followed along as Cody Volkenant of Addiction Motorsports bolted the Optimum-SR unit in Saoud's supercharged Pony. While the clutch kit and the hydraulic clutch-release bearing (PN 713402) and adapter (PN 730023) we installed can't be categorized as low-buck, they're quality choices for high-end Shelby 'Stangs with extra oats. Installing this setup is best left for the experts to handle, as exhaust and drivetrain pieces must be removed, and extremely detailed measurements are necessary for doing it properly.

Addiction Motorsports technician Cody Volkenant preps Quarter Master Racing Clutches’ all-new twin-disc clutch system for ’11-’14 Shelby GT500 ‘Stangs, while Saoud Alahmad’s ’12 Shelby waits patiently on the hoist to receive it.
Saoud’s ’12 is perfect fodder for a high-performance clutch system, as it’s equipped with such bolt-ons as long-tube headers, a smaller supercharger pulley, CAI, Ford Racing Performance Parts throttle body, and an Eddie Rios/SCT tune. The combination puts 580 hp at the feet with 680 lb-ft of torque—a blower upgrade (and fuel system) away from making the next-level power that is common for modified Shelbys.
Saoud’s ’12 is perfect fodder for a high-performance clutch system, as it’s equipped with such bolt-ons as long-tube headers, a smaller supercharger pulley, CAI, Ford Racing Performance Parts throttle body, and an Eddie Rios/SCT tune. The combination puts 580 hp at the feet with 680 lb-ft of torque—a blower upgrade (and fuel system) away from making the next-level power that is common for modified Shelbys.
Made primarily of billet aluminum, the Optimum-SR 10.4-inch clutch package truly is a beautiful piece. We had to give you this look at how nice it is before it’s hidden by the bellhousing.
After disconnecting the negative battery cable and securing the ‘Stang on a drive-on hoist, Cody removes the exhaust (long-tube headers must come off) and drivetrain ancillaries, and then pulls the Tremec T-6060 six-speed transmission away from the engine.
Here’s a side-by-side comparative look at the OEM twin-disc clutch package (left) and our Quarter Master unit. The new setup weights in at approximately 42 pounds, which is substantially lighter (about 18 pounds) than the stock Sachs twin.
Components in a twin-disc clutch system are stacked in the following order (from bottom to top): flywheel, disc, floater plate, disc, floater plate, pressure plate. Unlike other dual-disc systems, Quarter Master incorporates tall posts into the flywheel, into which the pressure plate is secured. The posts also serve as containment for the entire package.
When disassembling the clutch package, Cody indexes the correct position for the cover ring by marking common points on the ring and a flywheel stanchion. Doing this ensures the cover’s mounting straps are properly aligned.
The system’s billet floater ring contains holes that are designed to help dissipate heat and cool the clutch (by circulating air into the assembly), similar to the way ventilated brake rotors work.
Clutch discs are made from a high-metallic, proprietary, glass/polymer-based, organic friction material. Other systems rely on ceramic disc material.
The flywheel is installed first. Cody uses red Loctite on the ARP 7⁄16-inch bolts and torques the fasteners with 85 lb-ft.
While a pilot tool is a key element of any clutch install, using a good one is critical for dual-disc installations. Addiction Motorsports relies on a decommissioned T-56 input shaft (26-spline) for keeping things in line during twin-disc installs.
After installing the bottom disc (and making sure the flange side of the hub is pointed outward, toward the transmission), Cody mounts the floater plate to the assembly. Again, red Loctite is used and the fasteners are secured with 25 lb-ft of torque.
The pressure plate is the Quarter Master twin-disc system’s final component. Cody installs the plate so that its copper-colored cover is aligned with the flywheel stands, and then secures the cover’s fasteners with 30 lb-ft of torque.
Quarter Master’s hydraulic clutch-release (throw-out) bearing features a racing-inspired return spring design. In addition to air gap, this helps minimize continuous bearing-to-pressure-plate-fingers contact.
Unlike popular DOT 3/brake fluid that is used in hydraulic-clutch applications, Quarter Masters’ synthetic race-clutch fluid is designed to provide a solid pedal feel and consistent pedal actuation by maintaining its viscosity in high-temperature conditions. The fluid is available in individual 12-ounce bottles (PN 30100), and one bottle is included with the throw-out bearing.
Measurement C is the final value, which represents the setup height of the clutch (distance from the tip of the clutch fingers to the flywheel) and is taken with the assembly bolted onto the engine.
Setting the proper air gap (between the face of the bearing and the pressure plate’s fingers) is critical. Calculations for determining air gap must be made, and Addiction Motorsports owner Eddie Rios stepped in to help for this segment of the installation. After measuring the amount of crankshaft flange that pokes out of the engine block and noting it as Measurement A, Eddie and Cody use a straightedge and a 12-inch vernier caliper to measure the depth from the face of the bellhousing to the face of the bearing. The bearing must be fully compressed when this measurement is taken, and the thickness of the straightedge (0.100-inch in our case) must be subtracted as well. The result of this calculation is Measurement B.
After measurements are taken, performing the calculation of: Measurement A plus Measurement C, and then subtracting its sum from Measurement B will result in giving us the amount of air gap. Quarter Master recommends air gap be set at 0.150- to 0.200-inch; an assortment of shims is included for achieving this amount.
Here is a look at how the factory hydraulic clutch-release bearing (a sprung unit) measures up against the stout Quarter Master replacement. There really is no comparison here, as the stocker’s stamped chassis and anemic plumbing is clearly inferior to that of the new bearing. Fluid flow is from bottom to top with the Quarter Master throw-out (the top fitting/line is the bleeder).
AN -3 feed and return lines are routed from the bearing through the bellhousing, which must be modified slightly to accept them both.
Lastly, the hard line for the OEM hydraulic clutch is removed, and the new bearing’s feed line is connected to the master cylinder. This union is completely plug-and-play, thanks to a fitting that mates directly into the quick-release port at the firewall.
A few pumps of the clutch pedal ready the new unit for operation. The dual-disc combination, along with Quarter Master’s hydraulic throw-out bearing, give the new clutch a clamping force that’s rated at 2,200 pounds. However, unlike other clutch systems which require the leg of Samson to operate, minimal pedal effort is needed to disengage the Quarter Master. Like most clutch replacements (single or dual-disc), it’s highly recommended that a ‘Stang be driven for 250-500 miles before romping on the gas to allow the clutch to properly seat. 5.0