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.
The Centerforce clutch features a patented design, which relies on centrifugal force to increase its clamping pressure. The Centerforce clutch features weights attached to its diaphragm fingers. With rpm, these weights move outward and exert more pressure to the clutch-plate surface, the clutch disc and the flywheel. The result is a much greater clamping force, without heavier springs or a stiff pedal.
Centerforce offers three street versions of this clutch system. The original Centerforce I offers 30 percent more clamping power than an OEM clutch and is a great upgrade for a stock vehicle. The Centerforce II boosts the clamping pressure by up to 60 percent over OEM. It is recommended for mildly modified rigs and works well for heavy towing, commercial use and general four-wheeling.
Here is where it all started. Perhaps this former pilot bearing was never greased when the
On the left, what a Ford Power Stroke pilot bearing should look like. And on the right, wh
A look at the center of the OEM clutch disc shows the center splines tweaked from running
The Centerforce Dual Friction is the company's extreme-duty unit, and the one we chose for Jane. Providing up to 90 percent more clamping force than the stock unit, the Dual Friction is not just a cover, but also includes a disc. Centerforce's disc features carbon-fiber friction material laid out in a puck-type design. The Dual Friction is designed for high-horsepower/high-torque applications and is recommended for extreme four-wheeling.
Installing the Centerforce Dual Friction clutch is no different than installing any other clutch. To go with the all-new clutch assembly, Jane's flywheel was replaced with a new one from Centerforce. This assured that all the clutch-related components were new and balanced to one another. No part of the old clutch system was left in the bellhousing. In fact, even the bellhousing is different, it being integral with the transmission.
Jane has logged more than 5,000 miles with her Centerforce clutch and new tranny, with 3,500 of those miles towing the 9,000-pound load of Killer Bee Jeep and trailer to and through the mountains of Colorado, where she smoked two Dodges (pulling lighter loads) over several 10,000-foot passes. So far, the clutch has worked flawlessly. The only noticeable sign that major surgery has occurred is that the pedal pressure is slightly lighter than stock. This belies the fact that a much stronger clutch resides at the other end of all that plastic spaghetti. It is reassuring to know that Jane's clutch is now up to the task of dealing with her considerable power.
Along with clutches, Centerforce offers SFI-certified billet flywheels, allowing you to create a matched set for your new clutch. Modern hydraulic linkages offer no adjustment, and have very little tolerance for flywheels that have been turned down more than a few thousandths of an inch. When installing a new clutch, you always want to start with a fresh surface on the flywheel. By machining your old flywheel on a lathe, you achieve that new surface, but you cut down the overall thickness of the 'wheel. Cut too much, and the hydraulic throw won't compensate. You may find yourself thinking you've worn out a clutch in 40,000 miles, when its only the linkage that can't travel far enough to make up for the few thousandths of wear that's happened to the disc in those 40,000 miles. To avoid all this, a new Centerforce flywheel was installed in Jane.
All installed and ready for a tranny. All Centerforce clutch assemblies are fully balanced and they install just like any other clutch. In 5,000 miles of use, with more than half those miles spent towing something, Jane's new clutch has provided smooth engagement and a light pedal feel. Overall, she gives no hints that she has had major surgery.
Plain Jane - Part 1
Plain Jane - Part 2
Plain Jane - Part 3