The 49,676 miles it has seen so far don't seem like all that great a distance, but apparently they were too much for Plain Jane, our project Super Duty. Returning home from Los Angeles to northern Nevada with trailer in tow, Jane began shifting hard. Once cut loose from the trailer and used to run errands around town, she became downright stubborn and refused to shift into gear, or to even sit still at a traffic light with her clutch depressed.
Suspecting linkage, I first examined the all-plastic hydraulic master and slave cylinders, looking for a bleed screw. Finding none, I called Ford. This resulted in the purchase of a completely new hydraulic system, to the tune of 100 bucks. This plastic spaghetti, which consisted of a reservoir, some line, a master cylinder, more line and finally a slave cylinder, came pre-filled and pre-bled. Once installed (using no tools-it snapped together like Legos), Jane's symptoms were no better. Uh-oh. Out came the tools.
With her undersides scattered on the shop floor, the transmission's input shaft displayed disaster. The tip of it was the shape and size of my pinky-it should have been nice and round, and the size of my thumb.
Removing the clutch revealed the culprit. In the center of the flywheel, instead of a dime-size hole where a pilot bearing should have been, there was a quarter-size hole and no sign of any bearing. The outer race was still there, along with two little pieces of needle bearing, but that was it. The clutch's clamping surface was in fine shape, but its center showed signs it had been wearing at an angle for some time. The weight of that big 13-inch clutch, spinning around unsuspended and out of balance, did a number on everything aft of the missing pilot bearing-including destroying the $2,500 ZF six-speed transmission. To Ford's credit, it coughed up a remanufactured tranny-despite the fact that the truck's drivetrain warrantee had run out at 36,000 miles. As for the clutch, I decided that now was a good time to upgrade to a stronger unit.
Jane's Bank's-enhanced diesel is making 660 lb-ft of torque at her rear wheels, which means well over 700 lb-ft are twisting out of her flywheel and through her clutch. Centerforce's Dual Friction clutch cover, disc and SFI-certified flywheel are aftermarket pieces that can more than handle Jane's kind of torque.
Here is a comparison between the OEM clutch cover, or plate, on the left; and the Centerforce Dual Friction unit on the right. Note the square-shaped weights attached to the diaphragm fingers on the bright-orange Centerforce. These weights, when combined with the Dual Friction disc, create up to 90 percent more clamping force over the OEM unit. They rely on the centrifugal force inflicted upon them via engine rpm to do their job. The more rpm, the harder they clamp.
Now for a comparo of the OEM disc on the left, and the Centerforce Dual Friction puck design on the right. About the only thing they have in common is their 13-inch diameter. First, note that the Ford unit uses three large cushioning springs, while the Centerforce features four smaller ones. The OEM springs are known to rattle in their cages and are prone to breakage, due to their length and amount of surface area available for cushioning. Using four smaller springs increases the working surface area, cutting down on fatigue. Their tighter housings reduce the noise factor. In the friction area, the Centerforce features a carbon-fiber material with a much higher coefficient of friction than the OEM piece. This material can take considerably more heat before breaking down. The puck design contributes to the Centerforce's extreme clamping force. Picture a 100-pound woman walking on your back in tennis shoes. Now put that gal in stilettos and let her walk. The smaller area of those heels will concentrate that 100 pounds a whole lot harder than those tennis shoes would.