A Climax locomotive was a type of geared locomotive in which the two steam cylinders attached to a transmission located under the center of the locomotive frame. This transmission drove driveshafts running forward and backward to gearboxes in each driving truck. Unlike the somewhat similar Heisler design, there were no side-rods on the trucks; instead, the gearboxes drove both axles.
Climaxes were built in three distinct classes:
- Class A: these featured a steam engine unit with two vertical cylinders mounted in the center of the locomotive. Class A Climaxes had a frame similar to a flatcar with wooden boxcar-like bodywork built up above it to protect the crew and fuel from the elements -- this could be more or less covering between locomotive to locomotive. The front half of the locomotive, in front of the engine unit, contained the boiler; in smaller examples this may have been a vertical boiler, while in larger ones a tee boiler was employed. Class A Climaxes were small locomotives, generally under seventeen tons. Class A Climaxes, unlike Heisler and Shay locomotives, had two-speed gearboxes.
- Class B: looking more like a regular locomotive, the Class B Climax had the cylinders either side of the boiler, permitting it to be longer and larger than possible with the Class A arrangement. The two cylinders drove a transverse shaft that was geared to the longitudinal driveshaft in the middle; on early Class B climaxes, the cylinders were horizontal and pointing forwards, while later ones had the cylinders angled upwards at about 30 degrees from horizontal. Class B Climaxes weighed approximately 17 tons at minimum to a maximum of approximately 60 tons.
- Class C: As in the Shay locomotive, a class C was a three-truck design, the additional powered truck being beneath a fuel-carrying tender articulated to the locomotive. All Class C locomotives had inclined cylinders.
All Climax locomotives were built by the Climax Manufacturing Company (later renamed to the Climax Locomotive Works), of Corry, Pennsylvania. In addition, an agency and service facility was established in Seattle, Washington to sell and maintain locomotives for west coast buyers. Production began in 1888 and the last Climax locomotive was produced in 1928; between 1000 and 1100 were built.
Approximately 20 Climax locomotives survive in North America, of which about five are operational. In addition, two survive in Australia, including an operational example at the Puffing Billy Railway, and one in New Zealand, which also works.
Many loggers considered the Climax to be superior to the Shay, particularly in a smaller locomotive, although the ride was characteristically rough for the crew.
A number of Climaxes, especially Class A, were later converted to Diesel or gasoline power, and some still exist in this form, using the frame and drive mechanism of the original.