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On-demand front differential systems

12-12-2007

by Henri Lebarbé , moto123.com

Technology has evolved in many different ways since ATVs have begun offering available 4WD. Depending on the brand and model, buyers can either get a permanent 4WD system or a selectable 2WD/4WD setup. Take the Yamaha Big Bear 350 or Honda's TRX350 for example. Initially, they came with permanent 4WD and a limited-slip differential. In the mid 1980s, Suzuki jumped on the bandwagon with their 250-cc KingQuad that offered 15 forward gears and a locking differential. You could either lock the system in 4WD mode or select the 2WD mode.

2006 Honda FourTrax Rancher 4x4 ES

As I said, technology is much more sophisticated nowadays. For instance, Honda's Traxlok system uses an electromagnetic mechanical clutch unit to engage the differential. At Yamaha, engineers developed a unique "jaw clutch" controlled by an electric motor and an electronic module. These systems are activated by a switch mounted on the right handlebar.

Why so many systems to perform about the same task? And are these systems really that different? The answer is simple: a patented technology allows each manufacturer to make more money Sometimes, the innovations come from creative folks who don't have the financial means to develop and market their ideas. Therefore, they end up selling them to the highest bidder. The big manufacturers, in turn, end up taking these products for granted.

Engaging the 4WD mode could and should be done on the fly, without risking any damage to the engine or drivetrain. The front half of the chassis is often submitted to a harsh treatment (rocky terrain, steep climbs, logs, etc.), which means the differentials are constantly working and require extra efforts from the U-joint shafts. That puts heavy internal pressure on the differential gears. Power coming from the engine through the transmission then creates a counter-pressure on the front differential clutch mechanism, which requires a smoother riding to avoid any fluid-hammer effect.

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