The process of jacking, lifting and supporting tractors and trailers has resulted in more fatal accidents than any other aspect of truck tire and wheel service, according to industry data. Most of these accidents were the result of technicians' failure to use the proper procedures and/or equipment, specifically jack stands.
Jack stands are designed to support the load and include some type of mechanical lock (usually a pin) that prevents the vehicle from being raised or lowered.
They are adjustable and rated for a specific load that must be clearly indicated somewhere on the jack stand. They are rated and designed to be used in pairs on opposite sides of the same axle.
If the stand's rating is not visible or present, the jack stand should not be used. Their load rating must be greater than the weight of the axle being lifted.
When the capacity of a support stand is exceeded, it can fail with catastrophic results. Jack stands are not designed or rated to be shock loaded, so placing them under the axle or frame to act as stops in case the jack fails is not a smart thing to do.
Jack stands should be inspected before using them to ensure their components are not damaged or cracked. If needed, composite blocks may be used as support devices if they have a load rating.
Wood blocks should not be used since they cannot be rated for a specified load. Never weld any additional supports or make any alterations to a jack or jack stand.
ADDITIONAL RESOURCES: The Technology & Maintenance Council (TMC) of the American Trucking Associations created a valuable guide to help with this: Recommended Practice (RP) 262 Guidelines for Jacking and Lifting Tractors and Trailers. This offers guidelines for properly lifting, jacking and supporting Class 8 tractors and trailers with hydraulic jacks and jack stands using generally accepted lifting points.