I've been poring through the EMD F7 manual. Came across this little gem in Miscellaneous Operating Instructions (item 208): Operation over Railroad Crossings When crossing railroad crossings, reduce throttle to the 5th notch and leave reduced until all units are over crossing in order to reduce arcing from the brushes to the motor commutator. It may be this had been fixed by mods by the 1970s, but does give those of us who like to try and drive prototypically something else to remember
Even much newer SD50 still has this section in its manual. Maybe just to ensure you won't damage the older units in your consist, but it's there. US railroad crossings often offer quite bumpy ride, I've seen locomotives almost fly off encountering such bumps at higher speeds With DC traction motor commutator being a delicate piece of machinery, I can imagine it does not really like such treatment.