Class MC series - simpled (Locobase 7467)

Data from UP 10 - 1936 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection.

All 70 compound Mallets built to the same wheel arrangement (Locobases 7466 and 310) were obviously very satisfactory pusher locomotives for the Union Pacific. In 1937, the railroad decided to modify the cylinder layout to all live steam. It's a bit unusual for the rebuild to shorten the stroke on the drivers, which the UP did in this program. Tractive effort is listed as 89,840 lb on the diagram, which shows no grate area because these were oil burners. 46 sq ft (4.3 sq m) of the firebox heating surface came in the form of arch tubes.

The 70 locomotives were converted in 1937-1943. Some of the conversions operated until 1954.

Class MC-2/MC-3/MC-4/MC-5 (Locobase 7466)

Data from UP 10 - 1936 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection.

This low-drivered design was the first of a series of pusher freight compounds that by 1929 were running between Cheyenne and Laramie, between Ogden and Green River, between La Grande and Rieth and between Pocatello and Granger.

In addition to the Union Pacific's 15, the Oregon Short Lines took 1 engine of the Schenectady batch of MC-2s. These were followed in 1920 by 19 Brooks-built engines MC-3 of similar dimensions and greater weight; like the MC-2s, these had 15" (381 mm) piston valves on all four cylinders Brooks added 5 more MC-4s in 1922 along identical lines; Oregon Short Lines took delivery of 2 in 1923 and the OWR&N took 3. In 1923, Brooks added another 5 as MC-5s.

The last batch, delivered a year later, had a reduced tube count; see Locobase 310.

Class MC-6 (Locobase 310)

Data from tables in 1930 Locomotive Cyclopedia and UP 10 - 1936 Locomotive Diagrams supplied in May 2005 by Allen Stanley. Additional information from Gordon McCulloh via September 2012 email.

This last batch of Mallet Consolidations had twenty fewer tubes in the boiler than any of the earlier batches (for the latter, see Locobase 7466). The firebox heating surface area had 97.5 sq ft (9.05 sq m) of thermic syphons. Like the earlier engines, this class handled helper duties in Wyoming, running between Cheyenne and Laramie, between Ogden and Green River, between La Grande and Rieth and between Pocatello and Granger.

See Locobase 7467 for the simple-expansion conversion applied to all of these Mallets.