MSRRKevin Wrote:
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> I never fully understood the advantages of this
> design vs having the cab moved back just a few
> more feet.
Look at where the Johnson bars are in these photos. In each case the cab is centered over the Johnson bar.
Designers of that era couldn't have cared less about any form of ergonomics or about making life easier for engine crews. Their only goal was to move the train from point A to B.
The real reason for mounting the cab there, was because that was where it was convenient to mount the Johnson bar, and they didn't want it to hit the front of the cab. I assume that when railroads moved the cabs to the rear on some engines, that they found a new anchor point for the Johnson bar so it could be moved back to where the engineer could reach it.
The same thing holds true for camelback engines. On a conventional locomotive, the Johnson bar was connected to the valve gear by a reach rod which had to be substantial, rigid, and straight to carry the forces placed upon it. The wide Wooten firebox made a straight reach rod impossible, so since the designers couldn't move the valve control to the engineer, they moved the engineer to the valve gear. Look at photos of camelbacks. In every case, the cab is centered over the reverse shaft, and the Johnson bar is simply an extension of the reverse arm that the reach rod usually connects to.
With the advent of power reverses, cabs on camelbacks could be moved to the rear end again since the reach rod from the power reverse to the reverse lever (no longer a Johnson bar) carried very little force and could be made with bends and offsets in its length.