Class MT-1/MT-2 (Locobase 230)

Data from 1936 Union Pacific locomotive diagram book supplied in May 2005 by Allen Stanley from his extensive collection.

Originally delivered with Young valve gear and greater superheater surface, the only Mountains the Union Pacific ran were upgraded in the 1930s with Walschaerts valve gear and one-piece cast-steel frames; it is this upgrade that's shown in the data. When Railway and Locomotive Engineering's July 1922 issue featured this greyhound, the author commented on the "lightness of parts" that went into the design. He notes that the 2-8-2s then in service were not equal to the task of maintaining an average speed of 37 mph over the 484 miles between Ogden, Utah and Cheyenne, Wyoming; their drivers were simiply too small to meet the higher speed requirements. In addition, "It may not be generally known that there are grades west of Cheyenne in the Wyoming division of long distances running as high as 1.55 per cent on the westbound, and 1.14 per cent grades on the eastbound operation. Six through passenger trains pass over this region daily"

Then he noted the catch in using a 4-8-2 layout with taller drivers: "The only difficulty in introducing the mountain type of locomotive was in the recognized fact that the weight should not exceed 345.000 Ibs., for while the railroad, as is well known, is double tracked and of the most substantial construction, the numerous bridges, viaducts and other structures are not calculated to meet the requirements of heavier motive power than the weight referred to."

The result was a success: "[7000] has not been approached in point of design where boiler capacity in relation to weight is considered, and has only been made possible by a close comparison with other types where weights are known and by thorough tests of individual parts and material in order to ascertain what was possible as the looked for accomplishment, looking towards a general introduction of the mountain type of locomotive, if the success of the experiment should prove beyond controversy."

The diagrams show that many were fitted with a streamliner casing and bullet nosecap.