Constant velocity joint

A constant velocity joint is the articulated drive connection in a driven and steered front axle. It transmits torque from the front axle differential via the half shaft to the wheel hub, while allowing the wheel to move through its suspension travel and steer at the same time. Unlike a rigid half shaft, this connection must accommodate angular movement under load without noticeable variation in rotational speed. Knuckle joints are therefore used in front-wheel-drive or selectable four-wheel-drive MAN and Mercedes trucks, including vehicles for off-road and municipal applications.

The correct version is determined by the front axle configuration, differential, half shaft length, hub splines, maximum transferable torque and permissible steering and articulation angle. Depending on the axle design, these may be constant velocity ball joints, tripod joints or cardan knuckle joints with universal joints. Constant velocity versions are designed to maintain a uniform angular speed at the wheel hub, even at large steering angles; this limits torsional vibrations and load peaks in half shafts, hub reductions and differentials.

Cardan knuckle joints with universal joints consist of one or more universal joints between the driven half shaft and the wheel hub. The cross-shaped coupling allows the shaft to rotate at an angle when the wheel steers or the front axle moves through its suspension travel. Torque is transmitted from one yoke to the other via the bearing cups of the universal joint. In versions with two universal joints, the angles and yoke positions are matched to limit speed variations and maintain smooth power transmission to the wheel hub.

Always check the number of splines, spline diameter, retention by circlip or nut, flange size and the position of any ABS impulse rings. A knuckle joint must only be identified using the vehicle chassis number. Visual comparison, selection based solely on the model name or comparison of the outer splines alone is never sufficient, as the same vehicle series may have different front axles, load capacities and drive ratios.

Wear in the ball tracks, cage and running surfaces causes increasing radial or axial play. Typical symptoms include a rhythmic clicking noise when pulling away at full steering lock, jolts during load changes and vibrations under traction.

First raise the front axle safely, lock the steering gear according to the workshop procedure and check the half shaft for detectable play. Measure radial movement using a dial indicator on the shaft or hub flange; always assess the measured value against the axle manufacturer's tolerance. Rotate the wheel slowly while a second technician loads the driveline with the drive engaged. A detectable notch, scraping noise or uneven resistance indicates damaged running tracks. First rule out wheel bearing play, a worn kingpin and play in the steering rods, as these can cause similar steering and knocking symptoms.

Replace a knuckle joint when the ball tracks are indented, the cage shows cracks or the splines have play. Use only the specified constant velocity joint grease; universal chassis grease often has insufficient pressure resistance and an unsuitable base oil for this application.

Clean the splines thoroughly, check the fit for burrs and fit new locking devices and specified fastening nuts. Tighten hub and flange connections to the exact tightening torque and any specified angle of rotation set by the manufacturer. In addition to a wide availability of axle drive components, Braem can provide technical support for identification based on the chassis number and the correct combination of knuckle joint and required installation components.