49 C.F.R. § 230.111 – Spring rigging.

(a) Arrangement of springs and equalizers. Springs and equalizers shall be arranged to ensure the proper distribution of weight to the various wheels of the steam locomotive, maintained approximately level and in a safe and suitable condition for service. Adjusting weights by shifting weights from one pair of wheels to another is permissible.
(b) Spring or spring rigging condemning defects. Springs or spring rigging with any of the following defects shall be removed from service immediately and renewed or properly repaired:
1. (1) Top leaf broken or two leaves in top half or any three leaves in spring broken. (The long side of a spring to be considered the top.) Broken springs not exceeding these requirements may be repaired by applying clips providing the clips can be made to remain in place;
2. (2) Any spring with leaves excessively shifting in the band;
3. (3) Broken coil springs; or
4. (4) Broken driving box saddle, equalizer, hanger, bolt, or pin.