OK, it's my turn to be the skeptic. I don't believe this is what it looks like.
The Safety Appliance act specifically requires:
(v) Brake shaft shall be arranged with a square fit at its upper end to secure
the hand-brake wheel; said square fit shall be not less than seven-eighths
of an inch square. Square-fit taper, nominally 2 in 12 inches. (See plate A.)
So the hypothesized sliding brake wheel would be a safety appliance defect.
How do you secure a sliding brake wheel to a ROUND shaft anyway?
What's the use of dropping the wheel, if the shaft still projects to it's original height.?
Drop wheels as commonly used on flats have the wheel secured to the drop shaft, in compliance with the Act, and a square shaft that slides through the lower mechanisim .
If you zoom in very closely, I think you can see that the nut securing the wheel is in front of the supposed staff extension, which seems to be offset very slightly to the right.
Occam's Razor sez this is a broom handle or some such, perhaps used as a brake club, which was left sticking up from the coal, next to the brakewheel, and the photo happened to catch it at the right angle to create a nice illusion.