Feature > Manufacturer Profiles
Counting on Centerforce in a High-Pressure Situation
story by Steve Temple
photos by Steve Temple and courtesy of Centerforce
Some so-called experts feel that automatic trannies are better suited for off-roading than a stick shift. “There’s less interruption of power to the drivetrain,” or something like that, is their rationale. These off-pavement pundits probably live somewhere out on the prairie, undoubtedly a lovely place, but not exactly the center of flinty off-roading. And they’ve likely never even seen a serious speed shift much less executed one.
Manual transmissions may end up on the endangered species list, but many of us still prefer the ballistic surge that comes from winding up the engine, watching the tach needle climb to near red line, and dumping the clutch for a grunty launch.
On the flip side, we like downshifting, too; taking full advantage of the compression braking power of the engine. Practice is needed to get arms and legs to function into a smooth shift, so we’ll be damned if we’re going to let those hard-won skills go to waste from the insulating inertia of an automatic transmission.
Okay, back to the topic at hand. Note the colorful expressions employed in those passionate odes to stick-shifting: winding, dumping, surging. Now enhance them even more with the adrenaline-soaked sport of off-roading. Picture the stress on the clutch mechanism. Now you’re ready to hear about Centerforce clutches, an upgrade designed to absorb all the annihilating abuse that off-roaders can dish out.
The father of Centerforce clutches is Bill Hays. His résumé includes Air Force paratrooper and a nearly 25-year career as a fireman. In his spare time, he designed performance products and developed four automotive aftermarket companies. While Centerforce dates back to the early 1980s, Hays started building high-performance clutches in the 1950s, with an eye on the hot-rod and musclecar audience.
Hays Clutches were sold in 1968, but Hays himself continued designing innovative technology, such as the Centerforce Weighted Clutch System, which provides a combination of easy pedal pressure and superhuman clamping power. Following that, he developed the patented Dual Friction Clutch system and immediately earned new-product awards from the Specialty Equipment Marketing Association (SEMA) and HOT ROD magazine. Today, Hays’ company, part of Midway Industries in Prescott, Arizona, is still run by the second and third generations of Hays.
Don’t let the hot-rod applications confuse you. The same attributes that give rodders the ability to rev to red line before popping the clutch and peeling out are exactly what off-roaders need as they ride the clutch up and over elephant-sized boulders: durability, holding power, and a smooth, sweet pedal feel.
Just ask Will Baty, Centerforce’s multitasker for the last 16 years. Baty, whose tasks include media relations and first-hand research and development, powers his 1971 Bronco-an 800-horse, nitrous-infused off-road animal-through everything and anything, as we noted in a previous feature (“One Bucking Bronco,” July 2004).
Grinding machine. |
Computerized measuring equipment. |
Before we go into a description of why the Centerforce Clutch works so well for off-roaders, here’s a quick review of what clutches do, generally, and what Centerforce does better, specifically. (Much of this material is found in greater detail in Centerforce’s “Clutch Bible,” a useful reference every off-roader should have on his bookshelf.)
In the simplest terms, the clutch connects and disconnects the power of an engine to a super-duty transmission, allowing all that torque to spin those heavy, deep-treaded off-road tires. Applying the amount of clamping pressure to engage or disengage the tranny is no small task. Most original-equipment clutches are diaphragms, incorporating spring steel shaped in a Belleville configuration (picture a slotted disc, cone-shaped in the middle; when the raised center is depressed, it responds by popping over center). When the transmission is in gear, the Belleville spring is at maximum load or pressure.
Every time the clutch pedal is depressed, a domino effect is set loose within the clutch housing: An arm attached to the bellhousing pivots and pushes against the throw-out bearing. This bearing touches the Belleville spring, which pivots, releasing pressure from the pressure ring and disconnecting the clutch disc from the flywheel. The main shaft into the transmission is connected to the clutch disc and continues to spin at the same speed as the vehicle, but freeing up the tranny so gears can be shifted.
Two primary components of the clutch are the pressure plate and the clutch disc. The pressure plate has to apply and maintain just enough clamping pressure to the disc for engine torque to reach the driveline. The clutch disc is composed of a machined steel hub with splines that slip onto the main shaft of the transmission. This disc also has damping springs and stop pins, friction material on the disc faces, and the Marcell, a paper-thin, spring steel disc that takes all the engine-generated torque.
Covers ready for packaging and shipping.
If all this sounds like “the-thigh-bone-is-connected-to-the-hip-bone,” don’t worry. These details just give you a better idea of the constant pressure on a clutch and how seamlessly it has to work to keep a vehicle moving in the correct gear. If you’re getting a headache trying to picture the series of discs and springs, think how a clutch feels with its burden of friction and pressure. Just an everyday trip to work or the grocery store generates significant friction and heat.
Now think of what happens at the base of a granite boulder or when walking a 4x4 up a series of rock steps. Think of your foot on the clutch pedal in terms of a concert violinist caressing his Strad with a bow. You may have subtle finesse in your foot, but that’s no Strad keeping your Jeep clinging to the side of the rock.
Wrap your brain around the dynamics of the clutch, and it’s easy to assume that the heavier-duty the clutch, the heavier the pedal feel. That’s not necessarily true. Since most Centerforce Clutch-equipped off-roaders don’t have an alley-oop-sized left calf, there must be something else at work here. That’s centrifugal force, which Hays harnessed to maximize the clamping pressure with a relatively small amount of pedal pressure.
With clutch components already spinning at varying speeds, it was just a matter of designing a system that takes advantage of the force generated by that spinning. Hays did this by adding weights to the fingers of the pressure plate. As engine rpm increases, the weights move out, applying higher clamping force against the pressure plate and causing lockup at a faster, smoother rate. The faster, smoother the shift, the less friction generated, and the less clutch-lethal heat builds up. Plus, there’s less wear and tear on all the clutch elements, from the cable at the clutch pedal to throw-out bearings and all those components veteran stick-shifters blow out in midshift.
Level surface made of granite for precise measurements of part specs. |
Computerized measuring equipment. |
Centerforce’s Will Baty and other off-roaders appreciate the Centerforce technology when rock-crawling and using the engine to brake a 4x4 down a long, steep grade. “Rock-crawling is done at low rpms,” Baty points out (something even a novice roader knows). “So you end up riding the clutch to get the job done. With OE clutches, the heat build-up will result in clutch fade and slipping. Even though the centrifugal-force technology is based on engine speed, it works from idle on up, so you’ve got more holding power when you really need it.”
The same applies to those endless drops down rock-strewn grades: You’d love to fly down, but the only real way to make a controlled descent with you, your vehicle, and all its parts arriving at the bottom intact, is to use the engine’s braking power. This isn’t necessarily what original-equipment designers had in mind with stock clutches, but it’s a cakewalk for the Centerforce.
“When off-roaders upgrade to larger, off-road tires,” Baty continues, “unless they change out the gears, they’re adding a lot of extra weight and resistance to get that vehicle moving.” The same is true for deep sand and sucking bogs of mud, both of which require a lot of torque to the rear wheels. A standard clutch helps break that resistance to forward motion, but not as well and not nearly as long as a Centerforce clutch. Use and abuse (otherwise known as off-roading) eats stock clutches alive. Baty runs into a lot of Centerforce users on his 4x4 work adventures, off-roaders who have been abusing clutches for years, with no loss of holding power or signs of deterioration.
Baty recommends the Centerforce II for off-road applications. The II boasts 60-percent-more holding power than stock clutches and covers performance-modified 4x4s, oversized tires, and heavy-towing truck applications.
Other options include the Centerforce I, with a 30-percent increase in holding capability, recommended for light off-roading with stock tire sizes.
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For high-performance 4x4s (with nitrous-enhanced or turbo- or supercharged engines) like Beatty’s Bronco, go for the Centerforce Dual Friction clutch, designed specifically for high-horsepower, high-torque applications that generate near flash-point heat. The Dual Friction disc uses a specially formulated thermal resin compound on one side to maintain strong performance at higher temperatures. The opposite side has a non-asbestos disc facing for maximum capabilities at lower temperatures and smooth engagement.
So, for all you off-roaders who cling to the hands-on feel of a stick shift, and who have speed shifts down to a fine art, the next time you smell that ugly metallic aroma of a burning clutch, remember Centerforce. It’s a clutch player you can count on.