When a 3-piece truck is assembled there are clearances between components that are intended to allow relative movement, and to limit excessive movement. The magnitudes of the clearances are affected by manufacturing tolerances and wear in service. They have important effects on freight car dynamics including hunting stability and curving performance. A study has been made of the effect of varying clearances on the dynamic performance of a typical freight vehicle. The clearances that have been considered are in the areas of the: • sideframe window, • pedestal and bearing adapter • gibs • wheel diameters Combinations of maximum and minimum allowable tolerances and maximum allowable wear have been modeled with TTCI's NUCARS™ simulation software. Most of the test cases in the Association of American Railroads Manual of Standards and Recommend Practices, Chapter XI (1) have been studied. Results were produced from a NUCARS™ model of a 100 ton coal hopper. Empty and loaded simulations were performed. The trucks were modeled with variable load friction wedges. Conclusions have been drawn on the appropriateness of the currently allowable tolerances and wear limits. A new tolerance is suggested for the center of the sideframe window relative to the centerline of the pedestals. The conclusions only apply to the specific vehicle, suspension type and truck type analyzed. This work was sponsored by the Association of American Railroads, Strategic Research Initiative program.

Manual of Standards and Recommended Practices, Association of American Railroads, Washington D.C.
Field Manual of the AAR Interchange Rules, Association of American Railroads, Washington D.C.
Richmond, S., 2003, Effect of Tolerances on the Dynamic Behavior of a Three Piece Truck, Proceedings of the International Heavy Haul Association 2003 Special Technical Session, 2.1–2.8
NUCARS® User’s Manual, SD-043, Transportation Technology Center, Inc., Pueblo, Colorado
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