Lesson 2/Learning Event 2
the constant velocity joint. When assembled, each of the two center portions is able to
pivot (turn) between the other portion and the connecting axle. The axle shafts are
supported in the housing by bushings on each side of the constant velocity joint.
OPERATION OF LIVE FRONT AXLES
The operation of the final drive and differential assemblies in the live front axle is the
same as in a rear axle. Gear ratios to increase engine torque will be the same as those of
None of the front axle assemblies used in wheeled vehicles are designed to be operated
under power all of the time. Some vehicles have a control in the cab that permits the
driver to engage the front axle when it is needed. Other vehicles have a device made into
the transfer assembly to automatically engage the front-wheel drive when the rear tires
lose traction and spin.
When the vehicle is traveling straight ahead, both the inner and outer axle shafts are on
the same line. If the front axle is engaged to the power train, the inner axle shaft will
drive the CV joint. The CV joint will, in turn, drive the outer axle shafts which are
splined to the wheel hubs. As steering arms and rods turn the knuckles, the axle shafts
will flex at the CV joint.
During turns, the CV joint will continue to deliver a smooth, steady flow of torque. The
steering linkage moves both steering knuckles at the same time to the proper angle for the
LUBRICATION OF LIVE AXLES
Whenever the vehicle is moving, the gears of the final drive and differential are turning.
The lower part of the gearbox is filled with gear oil to a required level. The lower part of
the gearing passes through a pool of oil each time the unit rotates and thereby lubricates
all the working parts.
On some types of axle assemblies, oil flows down each axle shaft housing to lubricate the
bearings that support the outer ends of the axle shafts or wheel bearings.
Lubrication of the CV joints is generally done by packing the joints with GAA (grease,
automotive and artillery).