Bearings

Front axle bearings include the components that precisely support wheel hubs, steering knuckles and – on driven front axles – rotating drivetrain parts. These include wheel bearings, tapered roller bearings, cassette bearings, needle bearings, plain bearings, bearing bushes, spacer rings, locknuts and associated seals. These components absorb radial and axial forces generated by vehicle weight, braking forces, cornering and impacts from the road surface. Correct fitment, preload and lubrication are essential: excessive axial play causes unstable handling and brake disc runout, while excessive bearing load leads to overheating, seizure and premature failure.

For MAN and Mercedes trucks, buses and vans, bearings must always be identified using the vehicle chassis number. Visual comparison or selection based solely on the model name is never sufficient. Front axle versions differ in hub diameter, load capacity, ABS sensor ring, brake configuration, sealing system and bearing size, even within the same vehicle series.

Front axle bearings are generally used in wheel hubs with two tapered roller bearings: an inner bearing and an outer bearing. Cassette bearings provide a compact, sealed bearing solution in which the bearing and seal are designed as a single unit. This bearing arrangement enables precise adjustment of axial preload and withstands high combined radial and axial loads. On MAN TGL, TGM, TGS and TGX, MAN Lion's City and Lion's Coach, and Mercedes Actros, Arocs, Atego, Citaro and Tourismo trucks, buses and vans, dimensions, grease types, seals and locking systems may vary depending on the axle manufacturer and axle load.

In addition to hub bearings, steering knuckles may be fitted with bearing bushes, bronze plain bearings, needle bearings and axial thrust washers. Wear at these steering axle pivot points directly affects directional stability, tyre wear and steering precision. On vehicles with driven front axles, the bearing points around constant velocity joints, hub reductions or drive flanges must also be selected according to the correct axle version. Therefore, do not select solely based on a bearing's outside dimensions; also check bearing width, taper angle, sealing lip, installation position and the specified lubricant.

A humming or whining noise that increases with driving speed often indicates damaged raceways or pitting in the wheel bearings. A dull knocking sound when driving over speed bumps, making steering corrections or braking, on the other hand, may be caused by worn steering knuckle bearings, worn bearing bushes or insufficiently secured hub nuts. Leaking bearing grease on the inside of the wheel hub, discoloured brake discs and an abnormally hot hub are also important indications of a defective seal, incorrect preload or a bearing that has already suffered thermal damage.

Raise the vehicle safely and unload the wheel. First inspect the wheel hub for leaks, damaged dust caps and loose fasteners. Then measure radial and axial play using a dial gauge on the rim or hub flange. Compare the measured value with the vehicle-specific tolerances. Turn the wheel by hand and check for rough running, resistance or periodic clicking points. After a test drive, check the temperature on both the left and right sides with an infrared thermometer; a clear temperature difference may indicate increased bearing friction. Rule out brake problems before dismantling the hub: a dragging brake caliper or seized brake cylinder can cause similar heat marks.

Always replace wheel bearings as a set when raceways, rollers or bearing cages are damaged. Do not reuse bearing cups with new rollers, and do not fit new bearings onto a worn or corroded hub seat. Clean the hub thoroughly, inspect the fitment for scoring and, where necessary, measure the seat diameter and roundness. Press bearing cups in only via the outer ring; force applied to the wrong ring causes invisible damage to the raceways.

Use only the specified wheel bearing grease and do not completely fill the hub: excessive grease filling increases operating temperature. Adjust the bearings according to the specified tightening torque and the required end play or preload. Renew seals, locking plates and locknuts where specified. Correct installation prevents water ingress, grease loss and premature damage. Thanks to technical support and a wide availability of axle parts, Braem can assist with a well-founded selection for a durable front axle repair.