The importance of bearing preload (VIDEO)

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Modern wheel bearing assemblies are precision parts that are subjected to enormous loads while driving. Despite their strength and durability, they are vulnerable to certain forces that may arise during service.

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Wheel bearing assemblies are held together by a nut or bolt that secures the outer CV axle seal to the inside of the hub. Tightening this nut or bolt will place stress on the wheel bearing, which is known as preload. The purpose of preloading is to eliminate play inside the bearing and help it roll smoothly on the road.

Now, if there is no preload on the wheel bearing, that means there would be play between the rolling elements inside. If the entire weight of the vehicle were placed on the tires without preloading the wheel bearings, they would be damaged.

Let’s take the example of a 2017 VW Golf Alltrack. Volkswagen specifies that:

The drive axle bolt can be loosened a maximum of 90° when the vehicle is on its wheels. Vehicles without a drive axle must not be moved, otherwise the wheel bearing will be damaged.

To loosen the CV axle bolt you will need to jack the vehicle up so the wheels are hanging free, have a second technician press the brake pedal and hold it down while you remove the bolt. When reassembling the vehicle, have a second technician press and hold the brake pedal while you tighten the screw to 200 Nm, then lower the vehicle onto its wheels and turn the screw another 180°.

These procedures vary from car manufacturer to car manufacturer; that’s why it’s so important to read the OE service information before starting a repair.

We would like to conclude by briefly talking about orbital formed hub assemblies, also known as rolled-close hub assemblies.

These hub assemblies have a permanent preload which is set at the factory. Orbital formed hub assemblies are less likely to fail prematurely due to incorrect torque applied during installation, and offer a number of advantages including:

  • Reduced manufacturing costs
  • Reduced weight
  • Reduced size
  • And reduced preload tolerance

This video is sponsored by BCA Bearings.

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