M-R-S Manufacturing made a name for itself in designing and building large earth scrapers beginning in 1943. The letters stand for Mississippi Road Services, and the company had its start in Jackson, Miss., moving its headquarters 20 miles north to Flora in 1946. Filling the need for high-speed earthmoving vehicles, M-R-S concentrated from the outset on 4-wheel tractors with matching scrapers and wagons. The company's first efforts produced a 72-horsepower tractor coupled to a bottom dumping wagon holding 8 cubic yards or 13 tons. The outfit was known as the "Mississippi Wagon."
M-R-S believed the 4-wheel tractor concept provided better traction, higher speeds, and lower maintenance costs. The typical M-R-S scraper outfit consisted of a 4-wheel tractor pulling a standard 4-wheel pull-type scraper. This arrangement allowed any brand of scraper to be pulled by an M-R-S tractor as well as its own. Scrapers by LeTourneau or Bucyrus-Erie were often seen behind M-R-S tractors, but most common were scrapers built by Wooldridge Manufacturing of Sunnyvale, Calif. Wooldridge made pull-type scrapers adapted for M-R-S tractors, and were marketed by M-R-S as an integral unit.
A unique feature of the M-R-S design was the hydraulic weight transfer system between the scraper and the tractor. A long hydraulic ram extended from the tractor drawbar to a high point on the scraper gooseneck. Operation of this ram adjusted weight distribution between the scraper front wheels and the tractor rear wheels. More weight could therefore be transferred to the tractor wheels for increased traction in adverse conditions, or for self loading.
Some very large capacity scrapers were developed by M-R-S in the 1950s and 1960s. The 500-horsepower M-R-S 250 tractor, when coupled to the 41-yard heaped capacity Wooldridge OS-300B scraper, was billed as the world's largest rubber tired earthmover when launched in 1955. On a good haul road, the outfit could attain 34 mph in top gear. An even larger scraper, the 250-series, with capacities up to 65 cubic yards heaped, was available for the M-R-S 250 tractor in 1961. And some high-volume versions were offered for coal handling, including one of the largest volume single scraper bowls ever made, the model 250T, which could carry a heaped load of 90 cubic yards! This monster incorporated a 430-horsepower engine on the rear, and was drawn by a 430-horsepower M-R-S tractor.
In the 1960s, M-R-S offered elevating scrapers designed by Hancock Manufacturing and continued to offer 4×4 or 4×2 tractor and scraper combinations of both standard and elevating types throughout the 1970s. In 1986, Taylor Machine Works purchased M-R-S, and manufacturing was transferred to the Taylor Works at Louisville, Miss. After a few machines were built at the new location, orders dwindled and the line was discontinued by the end of the 1980s.
You can read more about the evolution of construction equipment in Keith Haddock's latest book, a softbound and updated version of his fully illustrated Earthmover Encyclopedia now available in book stores. Also, consider a membership in the Historical Construction Equipment Association, www.hcea.net. And be sure to visit ConstructionEquipment.com for past Iron Works features.