Southern Pacific class AC-4
Southern Pacific Railroad's AC-4 (meaning Articulated Consolidation) class of steam locomotives was the first class of 4-8-8-2 cab forward locomotives. They were intended to improve on the railroad's MC (meaning Mallet-Consolidation) class 2-8-8-2 locomotives with a larger firebox. Hence the four-wheel leading truck (instead of the two-wheel).
|Southern Pacific class AC-4|
Southern Pacific 4100 and its crew
The AC-4s were the first SP Mallets built for simple expansion. Baldwin Locomotive Works built them in August through October 1928 with a maximum cutoff of 70%, so tractive effort was rated at 112,760 lbf (501.6 kN); a few years later limited cutoff was dropped and calculated tractive effort increased to 116,000 lbf (520 kN).
The AC-4s were removed from service starting in 1953 and all ten were scrapped by June 1955.
- Diebert, Timothy S. & Strapac, Joseph A. (1987). Southern Pacific Company Steam Locomotive Conpendium. Shade Tree Books. ISBN 0-930742-12-5.