The Caterpillar 637 (also in Push-Pull configuration) Wheel Tractor-Scraper was based on the Caterpillar 631C Tractor unit and a new developed scraper unit, introduced in 1970 and only produced in America.
The first 637 had a Caterpillar D343 engine (Tractor) and a Caterpillar D333 engine (Scraper) combined producing 640 flywheel horsepower (FWHP) starting a series which lead from 637D (PP), 637E (PP), 637E Series II (PP), 637G and since 2016 todays latest Caterpillar 637K.
At present, the Caterpillar 637K Wheel Tractor-Scraper is the flagship of the 637 family. Powered by a Caterpillar C18 ACERT Engine (Tractor) and a Caterpillar C9.3 ACERT™ engine (Scraper) both good for 570.0 hp and 290.0 hp, an empty operating weight of 119060.0 lb and a loading capacity of 41.1 tons or 34.0 yd3 a serious piece of machinery in the range of Wheel Tractor-Scrapers made by Caterpillar.
Of the 637 Caterpillar Wheel Tractor-Scrapers are 1:50 scale model versions of the 637D in the Black Rat Model Collection and released CCM in brass the 637G Push-Pull (set) and 637G Auger (white version) and in die cast the 637E (PP), 637K PP and 637K Coal Bowl versions in 1:48th scale.