There are four main causes for hub failures:
- Lack of Lubrication
- Tight (over-torqued) axle nut
- Loose axle nut
Usually, hub failures are progressive and will produce some evidence of the failure. This will very often include damaged hub seals (leak), abnormal tyre wear (diagonal across), steering wheel problems, as well as the 3 “S” – smoke, smell and sound.
The bearing pre-load is adjusted by tightening the axle nut against the two cone-shaped bearings. While tightening the axle nut the complete hub assembly will get tighter and until there will be no more movement. As soon as the bearing pre-load is adjusted a cotter (split) is fitted at the axle nut to prevent the axle nut from moving.
A loose axle nut will allow the hub assembly to move side-ways (laterally) on the axle journal. The bearings will wear and the hub will become looser. The looseness of the hub will now allow excessive movement of the bearing rollers, causing roller cage wear and uneven race wear (scalloping). If this damage is not seen in time the play will increase and will eventually lead to hub failures.
If the hub axle nut is adjusted too tight, the lubricant between the bearing rollers and bearing races will break down. This is the same like a lack of grease, and the bearings will overheat causing bearing fatigue and hub failures. Subsequently this will cause a “bearing lock-up”. Further investigation will show fatigue marks on the bearings and severe heat discoloration.
Overloading the axles is the same like overloading the hub and like over-tightening the axle nut. The lead on the axle/hub forces the grease (lubricant) from the bearing rollers and bearing races causing heat and fatigue. Running on bad roads with big pot-holes will have the same effect like overloading.
Not enough lubricant causes metal to metal contact between the bearing rollers and bearing cages. This will result in excessive bearing and bearing race scoring with subsequent fatigue.
On hubs with a large outer bearing the oscillating hub can cause the axle nut to be pulled off the axle during a hub failure. In other cases where the axle nut is pulled of the axle, the thread will be ripped off the axle nut while the thread on the axle is normally undamaged.
On hubs with a small outer bearing hub failure, the hub can slip past the axle nut and the remaining parts of the outer bearing.
For more details on how to handle hub failures, contact your closest JMR branch.
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