what's new in: Clutches

With engine torques climbing in all classes of commercial trucks, one component that requires special attention in spec'ing, whether as original equipment or replacement, is the clutch. Whether they're building components for heavy-, medium- or light-duty trucks, clutch manufacturers are coming to market now with new or redesigned products intended to provide both longer life and better performance, despite those increasingly difficult operating conditions.

At the heavy-duty end of the market, the big news is the introduction this month of an automatic adjusting clutch designed specifically for the North American market, the ZF Sachs Twin XTend self-adjusting clutch.

Three years ago, Arvin Meritor sold its clutch manufacturing unit to ZF. With Arvin Meritor retaining the sales and field support duties for those clutches in North America, ZF turned over the engineering and manufacturing responsibilities to ZF Sachs, its European-based clutch division. While continuing to build the Meritor 15.5-in. manual-adjust twin-plate clutch, it immediately began development work on a new self-adjust model.

The most obvious advantage of a self-adjusting clutch is elimination of costly manual adjustments or even more costly failures from missed or improper manual adjustments. Yet only 30% of the heavy-truck market currently uses self-adjusting models, says Charles Auer, ZF Sachs engineering & sales manager for heavy-duty clutches.

The three most common problems cited by fleets as reasons for avoiding the low-maintenance option are early failures due to dirt buildup in the adjusting mechanism, mis-adjustments caused by vibration or shock loading, and poor gear shifting due to dragging clutch plates, according to Auer.

The new Twin XTend addresses the dirt ingestion with a “free flow” design that moves any dirt buildup away from the adjusting mechanism, according to Auer. A new locking mechanism on the self-adjustment portion of the clutch assembly solves the second problem by preventing vibrations or shock loads from mis-adjusting the clutch. And a controlled center plate mechanism adopted from the company's European models ensures full release of both clutch plates, resulting in better shift quality and even wear on all friction surfaces for maximum clutch plate life, he says.

The Eaton Fuller Solo clutch, marketed by the Dana/Eaton Roadranger operation, currently accounts for the large majority of self-adjusting heavy-duty clutches in service in North America. Recently updated with an extended lube option, the Solo is also available for medium-duty applications in two- and one-plate versions.

The latest version of the heavy-duty solo offers torque ratings up to 2,250 lb.-ft. and offers a wear indicator that makes it easy to visually check plate wear. It also features a new baffle design to protect the adjustment mechanism from dirt and a stainless steel cam spring to avoid vibration and shock loading problems. An increase in the side of the drive straps also decreases plate wear for longer service life. The Solo XL extends lubrication intervals from the standard 25,000 mi. to 50,000 mi. and includes a redesigned roller yoke intended to lengthen bushing and bearing life.

For Class 6 and 7 applications, the medium-duty Solo offers adjustment-free operation with torque capacities up to 1,150 lb.-ft. Like the heavy-duty models, it has dirt-protecting baffles and a visual wear indicator. The XL version eliminates the normal 10,000-mi. lube service with sealed-for-life release bearings and also features a new roller yoke.

While the trucks may be classified as light-duty, in commercial applications their components need to stand up to heavy-duty use. Clutches in particular have to be designed to withstand constant stop-and-go driving with near-capacity loads, towing, plowing and other conditions common for working trucks.

The Pro Gold line of high-performance clutch components is designed specifically for the torque, heat and extreme conditions created by those kinds of applications, according to the manufacturer LuK Automotive Systems. Available in replacement sets for most light-truck models, the Pro Gold packages include a new diaphragm spring clutch with high initial clamp load that actually increases as the clutch wears. The high-friction-coefficient facings are backed up by disc coils springs, hub flange and clutch diaphragm springs made for high-performance conditions.

The LuK Pro Gold kits include clutch and disc assembly, release bearing, pilot bearing and alignment tool. Matching high-performance flywheels are also available.