The Importance of Proper Bearing Preload During Installation

Modern wheel bearing assemblies are precision-engineered parts which are subjected to tremendous loads while driving. Despite their strength and durability, they are vulnerable to certain forces which may occur during service.

Wheel bearing assemblies are held together by a nut or bolt which secures the CV axle outer joint inside the hub. Tightening this nut or bolt will place tension onto the wheel bearing, which is known as preload. The purpose of preload is to eliminate clearance inside the bearing and help it roll smoothly down the road.

Now, if there is no preload on the wheel bearing, that means that there would be clearance between the rolling elements inside. If the full weight of the vehicle was placed onto the tires with no preload on the wheel bearings, they would be damaged.

Let’s look at a 2017 VW Golf Alltrack as an example. Volkswagen specifies that:

“The drive axle bolt may be loosened a maximum of 90° when the vehicle is standing 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’ll need to lift the vehicle, so the wheels are hanging free, have a second technician press and hold the brake pedal while you remove the bolt. When reassembling the vehicle, have a second technician press and hold the brake pedal while you torque the bolt to 200 Nm, then lower the vehicle onto its wheels and turn the bolt another 180°.

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

We’d like to conclude by briefly talking about orbital formed hub assemblies, also referred to as rolled closure style hub assemblies.

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

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

The BCA HUB video series brings together the latest video tech tips on wheel hubs, bearings and seals, featuring the experts you trust. Brought to you by BCA Bearings by NTN.