@Rich Melvin posted:When testing on a slip track, the locomotive is chained to the track.
Even if the grease was worn away, there is no "grabbing" of the rail. If the grease wore away, it would be just like a wheel slip when out on the road. Once the wheels start to slip, the friction between the wheels and the rail is so great that there is actually a tiny pool of molten metal between the wheels and the rail. That's why an engineer has to react quickly and slam the throttle shut to stop a slip. Here's a good example, with yours truly at the throttle:
Drivers spinning without grease on a slip track would not grab the rail, but they would quickly wear a dip in the rails as the drivers ground away at the rail with no lube.
Gotcha. Thanks! I wish the photo showed more of what was happening.