Bearings

The differential Bearings keep the pinion and the differential case with its crown wheel precisely positioned. This support helps determine the backlash, tooth contact pattern and noise levels of the bevel gear pair. Worn pinion bearings or differential case bearings allow components to shift under load, which can accelerate wear even on undamaged tooth flanks. A lasting repair therefore requires inspection of the roller bearings, bearing seats and lubrication, as well as the gear settings.

Always identify parts using the vehicle's chassis number, together with the axle code and the identification number of the installed differential. Visual comparison or selection based solely on the model name is never sufficient. Different axle versions and final drive ratios are used within the MAN TGS, TGX and Mercedes Actros or Arocs ranges. The exact drive axle must also be identified on buses and rear-wheel-drive vans, such as certain Sprinter and TGE versions. The available engine torque and permissible axle load influence the axle configuration; the engine family alone does not determine the choice of bearings.

Many designs use opposed tapered roller bearings to handle combined radial and axial loads. Other versions include additional cylindrical roller bearings for radial support. The bore diameter, outside diameter, width, contact angle, load capacity and internal geometry must match the specified design. Bearing rings and rolling elements are generally made of hardened bearing steel; cage material and heat treatment depend on the design. Identical external dimensions do not automatically mean the same load capacity or mounting height.

Essential adjustment parameters are bearing preload, pinion mounting depth and backlash. There are no universal values for these. Use the tolerances specified by the relevant axle manufacturer, including the distinction between new and used bearings. Lubrication is generally provided by gear oil through splash or circulating lubrication; operating pressure is not a selection parameter for splash-lubricated designs.

A rumbling noise that increases with vehicle speed may indicate damaged raceways. Whining that changes between driving under load and coasting may also be associated with an incorrect tooth contact pattern. Pitting, flaking, discolouration and damaged cages are signs of fatigue, contamination, insufficient lubrication or incorrect preload. A leaking pinion oil seal may also be caused by radial movement, rather than just a worn sealing lip.

1. During a safe road test, record when the noise occurs. Distinguish differential noise from wheel bearing, tyre and propshaft noise before dismantling.
2. Check the gear oil level, look for leaks and inspect the axle breather. Examine the drained gear oil and magnetic plug for metal particles; if in doubt, use oil analysis to assess water content and wear metals.
3. Measure axial and radial movement of the pinion flange with a dial indicator, following the workshop procedure. Also check that the flange is secure; a loose nut can cause similar symptoms.
4. Measure backlash at several crown wheel positions and check the tooth contact pattern with marking compound. Measure the pinion rotational torque using a suitable low-range torque measuring instrument, under the specified assembly conditions and allowing for seal drag.

Replace damaged tapered roller bearings together with their matching bearing rings; do not combine new roller assemblies with used outer rings. Use an outside micrometer and a dial bore gauge to check bearing seat diameter, ovality and fit. A bearing ring that has spun in its seat requires repair in accordance with the manufacturer's instructions or replacement of the affected component.

Apply fitting force only through the ring with the interference fit. Renew the specified locking components, seals and any collapsible spacers. Readjust the pinion bearings and differential case bearings; simply tightening the flange nut until the noise disappears is not a repair method. Clean the oil passages and axle housing, inspect the bevel gear pair and fill with the specified gear oil. Then verify rotational torque, backlash and tooth contact pattern, followed by a road test and a leak check. This prevents residual wear particles or incorrect preload from damaging the new bearings again.