Wheel hub

A front axle wheel hub forms the load-bearing, rotating connection between the wheel, brake disc or brake drum and the steering knuckle. The hub must reliably withstand high radial loads from vehicle weight and payload, axial forces when cornering, and peak loads caused by braking, potholes and kerbs. For MAN and Mercedes trucks, buses and vans, the correct version depends on the axle configuration, brake version, pitch circle diameter, wheel bolt or wheel nut system, ABS sensor ring and bearing arrangement. Therefore, always identify wheel hubs using the vehicle chassis number. A visual comparison or selection based solely on the model name is never sufficient.

Wheel hubs are fitted to, among others, MAN F90, F2000, TGL, TGM, TGS, TGX and TG3 trucks, TGE vans, and Lion’s City and Lion’s Coach buses. For Mercedes, this includes Atego, Axor, Actros, Arocs, Econic, Sprinter, Vito, Citaro, Intouro and Tourismo models. Even within a single vehicle series, differences may occur in front axle manufacturer, permitted axle load, brake diameter, track width and wheel mounting.

Depending on the design, the hub contains separate tapered roller bearings with a spacer ring and adjusting nut, or a pre-assembled bearing unit with cassette bearings. Cassette bearings combine bearing races, rollers and seals in a compact cassette. They require an accurate fit on the steering knuckle and in the hub bore; damage to the press fit, corrosion on the seating surface or incorrect installation force can immediately affect the preloaded bearing assembly. On versions with an integrated ABS reluctor ring, the correct number of teeth, sensor position and air gap must also be checked.

A humming, whining or cyclic droning noise that increases with driving speed often indicates pitting or raceway damage in the wheel bearings. However, steering wheel play, vehicle pulling, uneven brake pad wear or a scraping noise may also be caused by kingpins, brake calipers, brake discs or tyres. Diagnosis should therefore start with the vehicle safely jacked up and the front axle fully unloaded.

First check for leakage at the hub seal, grease traces on brake components and discolouration caused by overheating. Then measure radial and axial play at the wheel rim edge using a dial gauge, while moving the wheel alternately at the 12/6 o’clock and 3/9 o’clock positions. Compare the measured value with the manufacturer’s specifications for the relevant axle. Rotate the wheel by hand and check for a rough feel, clicking or irregular resistance. After a test drive, measure the temperature on both sides using an infrared thermometer; a noticeably warmer hub may indicate excessive bearing preload, insufficient lubrication or incipient bearing damage.

Replace a wheel hub when the bearing seats are worn out, the flange shows cracks, wheel bolts no longer clamp correctly or corrosion affects the seal and fit. In the event of damage to roller bearings or cassette bearings, it is advisable to replace seals, lock nuts, washers and, where applicable, ABS components in accordance with the instructions. Use only the specified wheel bearing grease for grease-lubricated hubs and observe the prescribed tightening torque and adjustment procedure for bearing axial clearance or preload.

A common issue is reusing a driven-in hub nut or installation using an impact wrench. This changes the bearing setting and can quickly lead to heat build-up, scored raceways and hub damage. Thoroughly clean the steering knuckle stub and hub bore, check dimensions and runout, and press bearing components only onto the ring intended for this purpose. Braem can support you with technically verified parts and broad availability for a fast, durable front axle repair.