Wheel bearings carry out two important jobs in your vehicle. They allow the wheel to rotate freely and with hardly any friction and they have to support the weight of the vehicle. Over many thousands of miles, they have to withstand very powerful forces. To do this job properly, they have to be in very good condition. Therefore, they must be packed with heavy grease. The purpose of the grease is to lubricate them and to protect them. A seal is provided around the bearing which is there to keep the grease in and water and other contamination out.

Here’s what you should consider when you are choosing your wheel-bearing grease.

• Is it water-resistant? Water resistance is an indication of the ability that the grease has to form a protective sheet to shield the wheel bearings against water and moisture. This is usually related to the oil content of the grease. Greases that are used in marine environments need to be very water-resistant. This allows them to protect metal parts from becoming corroded and so they last longer. Saltwater is a particular danger when it comes to corrosion.
• Will it withstand the extremes of temperature? Often you will see the temperature range of the grease stated on the container that it is supplied in. Beyond this stated range, the grease loses structure and breaks down. It no longer supplies lubrication or protection. Temperatures can get very high in the wheels of a motor vehicle so lookout for a grease that has a wide operating temperature range. Lithium greases are known for having a wide operating temperature range.
• Will it withstand high pressures? You need grease that will withstand the high pressures in a wheel. Sometimes the manufacturer will give a maximum pressure limit. In general, Moly EP greases withstand high pressures.
• What is viscosity? Greases have a range of viscosities or thicknesses. A grease that is rated as zero is very runny but a grease rated as six is very hard. Most greases for wheel bearings need a rating of two which is a bit like peanut butter!

If the grease is not there or becomes contaminated, it will not provide lubrication and there will be friction in between the wheel and the bearings. If there is no grease, the wheel bearings will start to corrode and break down. Ultimately the wheel will not be able to turn at all. An initial indicator that there is a problem will be an unusual noise that sounds a bit like a chirping or rumbling sound. Some wheel-bearing assemblies are completely sealed and you cannot apply more grease yourself.

All you can do is replace the whole unit. However, if it is not sealed, you need to remove and clean the bearings and pack them again with fresh grease. Don’t forget that the wheel bearings on trailers also need to be serviced and trailer bearing grease applied when needed. If wheel bearings fail, the wheel could actually come away from the vehicle and that is a very dangerous situation. Wheel bearings that are not adequately lubricated will not allow the vehicle wheels to spin quickly and evenly because there will be too much friction. This causes excessive and uneven wear on the tires and may damage other parts of the hub assembly.

If you have more questions about your wheel bearing grease and which one you should choose for your vehicle, give us a call at BMW Repair San Diego.