Wheel Bearing Failure and Why It Happens
Posted: Tuesday, December 28, 2010
by Perry Manku
The worst thing that could happen when out on your 4x4 adventure is you break down because your wheel bearings have failed. Wheel bearings are different according to make and model of 4x4 and the failure is down to the following factors:
· Contamination of the lubricant
· Lack of attention to bearing installation and maintenance
- Too little or too much lubricant
- The type of grease used.
- Increased vehicle vibration.
- Increase in "rolling noise."
- Elevation of operating temperatures which can show up as a burning odour at the affected wheel or even indications of smoke and lubricant leakage.
- Foreign matter introduced by careless handling and storage of the bearing prior to installation
- Foreign matter introduced during repacking by mishandling of the bearing or grease
- Not thoroughly removing old grease from bearings and hubs
- Repacking bearings while still wet with cleaning solvent
- Using wet or contaminated air during the drying process
- Entry of water or dirt during service due to faulty or incorrectly fitted seals.
- Poor inspection of bearings before refitting, resulting in the re-assembly of damaged bearings (etched, cracked, rusted, dented or in otherwise poor condition)
- Spinning dry bearings with an air jet
- Improper seating of bearings so that they do not track correctly
- Adjustment too tight or too loose
- Brake shoe clearance not properly adjusted
- Not greasing immediately after cleaning
- Use of impact tools including a hammer and punch. Bearing races or assemblies should be pressed into hubs and housings.
As the moving parts of a bearing come into contact with the grease, a small quantity of oil will be removed from the suspension agent (either Lithium or Bentone base) and adhere to the bearing surface. Therefore, the life of the grease is restricted to the amount of oil which can reasonably be extracted for lubrication purposes. Oil that is picked up is gradually broken down by oxidation or lost by centrifugal force and must be replaced from the reserve held within the grease packing. Not only does regular cleaning and repacking replenish the lubricant supply, removal of old grease cleans the bearing surfaces of dirt, oil depleted grease, abrasives, moisture, free acids and alkalis.
Greasing intervals depend upon the conditions under which the bearing operates and should be carried out at periods as recommended by the 4x4 manufacturer or bearing manufacturer.
Excessive amounts of lubricant forced into a bearing assembly causes the generation of internal friction and overheating, resulting in grease breakdown, hub seal rupture and premature bearing failure.
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