What's The Problem With Typical 4X4 ATV Front Differentials?

It's easy to take a front differential for granted. Usually, as long as it works, it can be ignored.

Riding along a dry, smooth trail, on a 4X4 ATV, steering's easy, and you don't notice the diff, doing its job-dividing the power between the two front wheels, yet permitting the outside wheel on a turn to rotate faster and farther than its mate on the inside; multiplying torque from the engine through its gear reduction . . .

Then, suddenly, you go off-road into gnarly-land; the rear wheels are in a slick mud hole, and an uneven, rocky surface kicks the front end up, raising one front wheel up in the air, off the ground . . .What happens now? Although you juice your steed with the thumb throttle, the rear wheels spin in the mud, the free front wheel spins helplessly in the air, and the other front wheel, resting solidly on a rock, doesn't turn at all-bottom line, the quad goes nowhere.

You say one front wheel, upon losing traction, spins helplessly on your 4X4 ATV? And the other front wheel, the one with traction, doesn't help at all, just SITS there? If only you could make that front wheel with traction turn; then, you'd be on your way. Is that what's bothering you?

Then rejoice, because ATV accessory distributor High Lifter, Inc., offers the Detroit Gearless Lockerä for quads; an automatic locking differential.

"'How does it know' when to lock, and when to unlock?" Tractech, Inc., built its first locking differential, the Detroit Lockerä, over 50 years ago

Normally, the Detroit Gearless Lockerä remains locked. Clutch housings and side couplers mesh splines, mechanically and positively locking drive axle half-shafts together.

When making a turn, ground force drives the outside wheel faster than the inside wheel, overcoming the differential clutch lockup force, freeing the outside wheel to rotate faster. Yet, the inner wheel remains locked to the differential carrier, driving with full power.Upon completing the turn, the wheels resume rotation at the same speed, the outer wheel's differential clutch again locks up, and the two wheels turn as one.

The Detroit Gearless Locker uses a unique "clutch" system, unique because, unlike conventional clutch packs found in typical "limited-slip" differentials, these clutches lock, in contrast to slipping.

The Detroit Gearless Lockerä clutch system consists of two clutch housings, somewhat like a steel disk, sliced into two halves. Each clutch housing has a V-shaped trench cut radially across its inside surface; these V-shaped trenches accommodate the differential cross pin.Other components include two side couplers, replacing the original axle side gears and splined to each axle half-shaft; and two packs of sheet steel "clutch disks," tabbed to fit clutch housing and side coupler splines.

The V-shaped trench and cross pin (called the "Tunkenel-V Power Driverä" after the Tunkenel-V steel alloy used in manufacture), provides the locking force for the differential.

When the driveshaft applies torque, turning the differential case, the cross pin presses against the ramps formed by the surfaces of the V-shaped trenches in the main clutch housing halves, separating these components. This separation, the Tunkenel-V Power Driverä system action, forces clutch housing halves and side couplers (replacing side gears) together, engaging their splines and effectively locking the differential. While at rest, two springs separate the clutch housing halves, locking the axles together.

When turning, ground speed forces the outside wheel ahead of the differential carrier rotational velocity, overcoming the clutch separation force and reducing the V-ramp pressure on the associated clutch housing half, permitting that clutch housing to close nearer to its mate. The outside clutch housing moves in toward the center, permitting withdrawal from the side coupler splines, unlocking the faster-turning outside wheel. Meanwhile, the inner wheel continues driving with full power.

While the outside wheel is unlocked, the outer axle remains connected to the differential case through the friction of the clutch pack disks. When the vehicle resumes a straight path again, with both wheels turning at the same speed, the Detroit Gearless Lockerä "locks up" as before.

We had a chance to ride a Honda 450 ES with a prototype Detroit Gearless Lockerä installed.

In a short ride over pavement and an unimproved field under light throttle, the steering seemed identical, regarding turning effort and response, to the machine's performance before the installation.

The Foreman turned easily, with no noticeably objectionable ground scuff, indicating outside front wheel release in turns, "as advertised."

While an automatic locking differential characteristically brings some "slack" or "play" to the driveline, we noticed no associated problem when riding the 450 ES.

Sometimes an automatic locker releases at an unpredictable moment in a turn, creating a sudden change in steering characteristics. During the brief prototype ride, engagement and release were smooth; however, all riding was under moderate throttle-a later full-scale evaluation will examine locker behavior under more extreme conditions.

No exhaustive off-road mud-hole evaluation of the pre-production Detroit Gearless Lockerä was possible at the time of our ride; look for a full ATV Magazine operational test and evaluation when High Lifter releases this new product for commercial sales.

Expect initial production models available for Honda 450, 300, and 400 Foreman ATVs, with kits for other makes and models to follow.

With a Detroit Gearless Lockerä, two drive wheels are normally locked together; however, the outer wheel may release and rotate faster than the inner wheel in a turn. The inner wheel remains locked, driving with full power at all times. Releasing an outer wheel in a turn promotes easier steering, reducing drivetrain stress and tire tread wear. If a wheel loses traction, it never spins faster than the wheel with traction, as with a conventional differential. "There can be no one-wheel spinout."