A hand brake left on or a sticking brake can lock a wheel so it skids, grinding a flat into the tread. The flat hammers the rail once per revolution with a loud, rhythmic thump, cracking rails and damaging bearings. Federal freight car rules condemn a wheel once a single flat reaches 2.5 inches long, and wheel impact detectors along the line flag the worst offenders.
Heard on the job
Somebody left a hand brake on, we've got a flat spot thumping on the 30th car, you can hear it from here.
Also heard as
- flat wheel
- slid flat
- flat