KJ Jones
February 4, 2014

Horse Sense: Although they are wear items, clutches typically can last for thousands of miles of non-abusive driving in stock 'Stangs. However, as we've learned over the years, horsepower will seek and ultimately destroy the proverbial weakest link in a stocker's drivetrain. Weak links are exposed by aforementioned wear, and also by making modifications designed to increase a Mustang's performance output. It only makes sense that the clutch receive some love as well, because when you consider that weak-link theory, OEM hardware will probably fail pretty quickly when power increases.

It has been said that the shortest distance between two points is a straight line. We certainly endorse that idea, especially when it comes to getting to the far side of a dragstrip. There's no disputing that when a 'Stang's quarter-mile performance is being measured by the e.t. clocks, nothing beats the direct approach.

When applying this concept to a Mustang's horsepower, which is arguably its most- important performance criteria, big steam definitely requires a straight, true, and solid link between a Pony's engine and its hooves. While it's imperative that the engine, transmission, driveshaft, and rearend are good and lined up properly, having a clutch system that's up to the task of harnessing the engine's grunt is just as crucial for stick-shifted Mustangs.

The clutch is the first component that helps maintain the solid part of the link equation, keeping the transmission's input shaft turning in 1-to-1 unison with the engine when you go hard on the gas and rpm starts to climb. Slip is the result of the clutch's inability to corral an engine's power and torque. It is the most common form of clutch failure, caused by deteriorating clutch-disc lining or flywheel surfaces, usually brought about by excessive heat.

Earlier 'Stangs feature single-disc clutch systems, while some of the newer SVT Ponies are equipped with twin-disc setups from the factory. As you can imagine, there are limits to the amount of power and torque that a clutch design can handle. So, when increases come about, appropriate changes must be made. With horsepower and torque values scaling beyond 700 horsepower and 650 lb-ft of torque, more discs are usually needed to survive and retain an acceptable pedal effort. Twin-discs spread torque load out over several surfaces, reducing inertia, and increasing clamping forces. But lower inertia can result in trickier engagement if it's not dialed in for the application.

This doesn't mean Ponies with less horsepower are excluded from using multiple clutch discs. To the contrary, there now are dual-disc clutch systems designed for both race and street applications. These iterations of the twin-discs feature enhanced clamping force thanks to heavier pressure plates and greater inertia for smooth engagement and lower pedal effort. Basically, today's dual-disc clutches and hydraulic clutch-release bearings certainly can aid a 500hp blown 'Stang the same way they will a twin-turbo'd beast that makes twice as much power.

This month we're detailing the installation of Ram Clutches' Ram Force Series 10.5-inch, dual-disc street clutch (PN 80-2260) and hydraulic release bearing (PN 78175). Ken Stevens stepped up with an appropriate candidate—a '10 GT that sports a 2.6-liter Kenne Bell supercharger atop its stock Three-Valve engine. The Ram Street Dual Force 10.5 is actually well-suited for Ken's 475hp/412–lb-ft street 'Stang, as its higher inertia is more conducive to good low-speed driveability than its lower-intertia counterparts.

Our association with brothers Ricardo and Gonzalo Topete of GTR High Performance in Rancho Cucamonga, California, is fortunate. GTR has a long roster of customers like Ken, who are always available during our time of tech-project need.

Read along with the accompanying photos and captions covering the clutch swap, which was performed by GTR's wundertech Eddie Zapata.

After pulling the catalytic converters away from the exhaust manifolds on Ken Stevens’ ’10 Mustang GT, Eddie Zapata of GTR High Performance (www.gtrhipo.com) drops the ’Stang’s manual transmission, to access and begin exchanging the stock clutch assembly for Ram’s 10.5-inch street-twin setup.
After pulling the catalytic converters away from the exhaust manifolds on Ken Stevens’ ’10 Mustang GT, Eddie Zapata of GTR High Performance (www.gtrhipo.com) drops the ’Stang’s manual transmission, to access and begin exchanging the stock clutch assembly for Ram’s 10.5-inch street-twin setup.
Upon removing and inspecting the single-disc, OEM clutch in Ken’s GT, it’s clear the unit is ready to be replaced. Not only is the disc material worn down, the nodular-iron flywheel shows signs of cracking and excessive heat in a few areas.
We’re replacing the stock hardware with Ram’s Force Series 10.5-inch, dual-disc street clutch (PN 80-2260; $1,298.97) and hydraulic release bearing (PN 78175; $399.97).
Here’s a closer look at the Ram setup, which includes a billet-aluminum flywheel, a floater plate, two clutch discs, and a diaphragm-style pressure plate.
The 10-spline clutch discs features Ram’s 300 Series organic material, which is bonded to a steel backing plate that increases heat dissipation and provides excellent structural strength without compromising driveability or high-rpm performance. Early dual-disc clutch systems were designed with solid hubs and viewed as hard-core racing parts that were not recommended for street use due to their Off/On operating characteristics. The new Ram disc’s sprung hub features urethane- covered, poly-coil springs, which help absorb high torque loads instead of transferring torque directly onto the disc and shocking the drivetrain (which can damage the clutch discs).
The kit includes a billet-aluminum, 1 1⁄16-inch, six-bolt flywheel, which at approximately 15 pounds, is considerably (nearly 10 pounds) lighter than the OEM nodular-iron wheel.
Eddie secures the flywheel with the original bolts, torqued to 85 lb-ft. Notice that the nuts are placed on each stand. Ram recommends this to ensure the stands and shims don’t end up being MIA during its installation.
After installing the bottom clutch disc (the bottom disc has a solid hub that must be mounted with the large-diameter side facing the transmission), Eddie sets the floater plate in place. Small shims are placed between the floater’s straps and the flywheel, and Loctite must be applied to the bolts before tightening them down with 20 lb-ft of torque.
The top disc (sprung hub) sits atop the floater. GTR uses a repurposed 10-spline input shaft as a clutch-alignment tool to ensure the transmission can be reinstalled without much heavy effort.
The pressure plate/cover is the final piece of the Ram twin-disc clutch package. Eddie confirms the previously made alignment marks (small references on the cover and flywheel that Eddie made before) all match before calling the procedure done.
Setting the air gap (between the face of the bearing and the pressure plate’s fingers) really is the only part of the operation that can be somewhat confusing, as detailed calculations must be made to ensure air gap is sufficient. The first measurement (A) is taken at the engine and equals the amount of crankshaft flange that pokes out of the engine block. Next, with the throw-out bearing compressed, Ricardo uses a straight edge and a vernier caliper to measure the depth from the bearing face to the face of the bellhousing. This is measurement B. Finally, measurement C is the distance from the tip of the clutch fingers to the flywheel, better known as the setup height.
Setting the air gap (between the face of the bearing and the pressure plate’s fingers) really is the only part of the operation that can be somewhat confusing, as detailed calculations must be made to ensure air gap is sufficient. The first measurement (A) is taken at the engine and equals the amount of crankshaft flange that pokes out of the engine block. Next, with the throw-out bearing compressed, Ricardo uses a straight edge and a vernier caliper to measure the depth from the bearing face to the face of the bellhousing. This is measurement B. Finally, measurement C is the distance from the tip of the clutch fingers to the flywheel, better known as the setup height.
Here is the Ram hydraulic clutch-release (throw-out) bearing/slave-cylinder assembly. The bearing’s adjustability and increased travel (over the factory hydraulic piece) helps ensure that fingers on the pressure plate do not make contact with the bearing when the clutch is engaged.
After removing the stock hard line that feeds the throw-out bearing, Eddie installs Ram’s new braided line, which pops right into the master cylinder at the firewall using the factory fitting. With the exception of road-testing Ken’s ’Stang and then driving roughly 500 miles to properly seat the new clutch, making this connection basically completes the dual-disc clutch install. While the Force 10.5-inch setup will support approximately 1,100 lb-ft of torque, its top disc's sprung hub and the hydraulic bearing provide quiet smoothness and pedal effort similar to that of the original equipment.
The clutch-release bearing slips over a collar that bolts to the transmission. Notice the two AN -3 fittings that Eddie installed in the bearing’s slave cylinder? The fittings support braided line that routes hydraulic fluid into and out of the cylinder, and in turn moves the bearing’s piston back and forth.
Here is the assortment of steel shims that are included with the clutch system. The shims are used for adjusting the depth of the clutch-release bearing and fine-tuning the air gap. After measurements are taken, measurement A is added to measurement C, and then the sum of this equation is subtracted from measurement B. The amount of air gap typically should be set at 0.1500- to 0.200-inch. This routine (removing and installing the transmission and re-measuring) definitely will become repetitive if you miscalculate, so it’s important to take your time and be careful when recording this data.
DOT 3 brake fluid is used for the Ram hydraulic throw-out bearing. The AN -3 braided line on the right is the actual fluid feed for this system; the line on the left is the bleeder circuit.