Brake Tests

144 work done. Therefore, the use of two shoes per wheel results in less shoe wear in doing a given amount of work, than is the case with one shoe per wheel. 310. (G) Maintenance and repairs to brake rigging and cost in- cident thereto, may be reduced to a minimum by providing ample bearing area for all pins and case hardening all bearing surfaces, and bushing pin-holes wherever practicable; also by making as many parts interchangeable as possible and by designing and installing the equip- ment so that wheels, brake shoes and rigging parts may be conveniently and quickly removed and replaced. Proper means should be provided for uniformly taking up slack in the rigging. 3H. (H) Correct replacement in making repairs can be insured by having as many parts of the rigging as possible interchangeable and at the same time making parts which are not supposed to be inter- changeable of such dimensions and proportions as to preclude the possibility of using them at a point in the truck where they are not intended. 312. (1) The initial and maintenance cost should be as low as consistent with, but secondary to the points mentioned above.