49 CFR § 230.77
Foundation brake gear
November 18, 2020
(a) Maintenance. Foundation brake gear shall be maintained in a safe and suitable condition for service. Levers, rods, brake beams, hangers, and pins shall be of ample strength, and shall not be fouled in any way which will affect the proper operation of the brake. All pins shall be properly secured in place with cotter pine, split keys, or nuts. Brake shoes must be properly applied and kept approximately in line with the tread of the wheel.
(b) Distance above the rails. No part of the foundation brake gear of the steam locomotive or tender shall be less than 21⁄2 inches above the rails.