49 CFR § 215.119 - Defective freight car truck.
A railroad may not place or continue in service a car, if the car has -
(a) A side frame or bolster that -
(1) Is broken; or
(2) Has a crack of 1/4 of an inch or more in the transverse direction on a tension member;
(b) A truck equipped with a snubbing device that is ineffective, as evidenced by -
(1) A snubbing friction element that is worn beyond a wear indicator;
(2) A snubber wear plate that is loose, missing (except by design), or worn through;
(3) A broken or missing snubber activating spring; or
(4) Snubber unit that is broken, or in the case of hydraulic units, is broken or leaking clearly formed droplets of oil or other fluid.
(c) A side bearing in any of the following conditions:
(1) Part of the side bearing assembly is missing or broken;
(2) The bearings at one end of the car, on both sides, are in contact with the body bolster (except by design);
(3) The bearings at one end of the car have a total clearance from the body bolster of more than 3/4 of an inch; or
(4) At diagonally opposite sides of the car, the bearings have a total clearance from the body bolsters of more than 3/4 of an inch;
(d) Truck springs -
(1) That do not maintain travel or load;
(2) That are compressed solid; or
(3) More than one outer spring of which is broken, or missing, in any spring cluster;
(e) Interference between the truck bolster and the center plate that prevents proper truck rotations; or
(f) Brake beam shelf support worn so excessively that it does not support the brake beam.