Issue link: http://read.dmtmag.com/i/34501
HOW TO CHECK AXLE PARALLELISM AND TRACKING: With the vehicle on a flat surface and with the suspension in a relaxed position, select two points on the front and rear axles. These two points on each axle must be equal distance from the chassis center (e.g., at the point where the springs meet the axles). Using a plumb line, mark four points on the ground, move the vehicle away, and measure the distance between the marks as shown on the diagram. A more detailed field type procedure is recommended by Michelin Alignment – Field Method (Pages 118-119). ® and can be found in the Section Nine, Appendix under For Truck/Tractor: The Technology and Maintenance Council recommends no more than 1⁄8 inch between axle ends. If AD = BC and DE = CF, the axles are parallel. If X = X’ and Y = Y’, the wheels are symmetrical or tracking. For Trailers: The Truck Trailer Manufacturers Association (TTMA) recommends no more than 1⁄16 inch between axle ends and 1⁄8 inch maximum from the trailer kingpin to the lead axle ends. If AD = BC and CE = DE, the axles are parallel and symmetrical. (Reference: TTMA RP No. 71 Trailer Axle Alignment.) X' X' X Y Y' Y Y' X 52 Section Three: Extending Tire Life