Wooldridge TD-8 blade on a Caterpillar D-8 tractor.
Wooldridge Manufacturing Company founder Mack Wooldridge (1890-1962) was one of the early pioneers of the earthmoving industry. Like R. G. LeTourneau, M. W. Baker, E. W. LaPlant, Roy Choate and Garfield Wood, he saw the utility of attaching a blade to a crawler tractor when tractors were in their infancy. Wooldridge grew up in California, became a mechanic and developed a strong interest in crawler tractors. In the mid 1920s, he opened a dealership for Cletrac tractors in southern California and soon began custom-building hand-operated blades and other attachments for the tractors he sold. He incorporated under the name Mack Wooldridge, Inc., with a head office in Los Angeles, Calif., and a branch in Birmingham, Ala. He also built snowplows for crawlers that he sold to dealers in the Midwest.
In the late 1920s, Wooldridge became interested in the new hydraulic lifting technology that had been developed for dump trucks and saw an application to lift and apply downward pressure on dozer blades. His first hydraulic blade had only one hydraulic cylinder to lift the blade, which was attached to lifting arms by chains and thus could not exert downward pressure. Wooldridge applied for a patent for this design in 1928 and it was awarded in 1931; he would receive over a dozen patents for construction equipment in his lifetime.
Wooldridge kept improving his blade design, and soon had a line of hydraulic blades for Cletrac models 20, 30, and 40. Young and Budy recount a story of Wooldridge and his early dozer blades in Endless Tracks in the Woods. In 1928, the U.S. Forest Service held a demonstration of road construction equipment in Santa Barbara, Calif., with a stipulation that only “proven” equipment would be shown. The demonstration was to include a tractor-drawn road grader, gas-powered shovel, and several horse-drawn Fresno scrapers. Forest Service engineer Ted Flynn, another dozer blade pioneer, unofficially invited Wooldridge and asked him to bring one of his Cletracs with a hydraulic blade. Unannounced, Wooldridge drove the tractor into the show grounds and proceeded to show how well the dozer could perform, while most of the other machines either broke down or performed poorly. The officials at the demonstration were duly impressed, and the event received favorable reviews in the newspapers and trade journals. Because of their horsepower to weight ratios, differential controlled steering, and smaller size, Cletrac tractors had become the favored make in forestry and agriculture, and Wooldridge had an early edge on supplying blades for them. The Forest Service in particular purchased large numbers of Cletracs with Wooldridge blades for building trails and opening new roads in the National Forests.
During the early 1930s, what was now called the Wooldridge Company expanded its blade line to fit other crawler makes, and began building towed implements including rippers and scrapers. Around 1931, Wooldridge was contracted by Continental Roll & Steel Foundry Company to build scrapers at its Los Angeles plant. In 1935, two of the Wooldridge employees responsible for building scrapers under this contract were hired by Bucyrus-Erie to design its new line of scrapers and dozer blades. On its end, Continental produced straight and angle dozers for crawler tractors under the patents held by Wooldridge.
Wooldridge received his first patent for a towed scraper in 1934, and was soon offering them in several sizes. To compete with LeTourneau’s Carryall scraper line, Wooldridge adopted the name “Digancary.” Digancary scraper capacities ranged from 2½ to 12 yds.; the two largest models could be ordered with either a PTO-operated hydraulic pump or with its own gas engine to power the hydraulic controls, allowing it to be pulled by a bare tractor. A 30-yard dump wagon with 16 wheels also was offered. Unlike most of the other blade and scraper makers of this era, Wooldridge did not become an allied supplier of attachments to a crawler tractor manufacturer.
Wooldridge was one of the first equipment makers to offer a training program for operators. In 1931, he started a school for bulldozer operators under the direction of the Civilian Conservation Corps, which was either constructing or funding construction of public works projects all over the country.
In 1938, Wooldridge partnered with Harold Gusman to form the Wooldridge Manufacturing Company, and opened a new factory in Sunnyvale, Calif. Gusman was listed as president, and Wooldridge was vice president. The arrangement did not last; the next year, Woodlridge left the company and became president of ATECO (American Tractor Equipment Corporation), another California-based manufacturer of attachments and allied equipment for crawler tractors. (For clarity’s sake, all Wooldridge citations from this point forward are to Wooldridge Manufacturing, not Mack Wooldridge unless he is specifically named).
Under Gusman, Wooldridge produced blades, rippers and scrapers similar to what Wooldridge’s former company was selling, but with the addition of a 25-yard scraper with six rear wheels. Recognizing the increasing demand for scrapers, Wooldridge Manufacturing concentrated on developing a full line of one- and two-axle models, and changed the name to Terra Clipper. However, the limitations of hydraulic technology at the time probably caused Wooldridge to choose cable operation for its implement line. (Contamination from dirt was one of the problems of early hydraulics, and Mack Wooldridge hired a University of Southern California engineering student, Harry F. Vickers, to solve the problem. Vickers did so, and went on to great success in the field of fluid power; the American Society of Mechanical Engineers called him the father of industrial hydraulics and, in 1956, awarded him the ASME Medal to recognize his “eminently distinguished engineering achievement.”)
By the early 1940s, all Wooldridge blades, rippers and scrapers were cable-operated, and the company added a line of cable-control units in one-, two-, three- and four-drum configurations. The Terra Clipper scrapers ranged in capacity from 6 to 28 yds., and models were designated by a single letter preceded by “TC”. The larger models were offered with four rear wheels as an option, and the largest had the option of four wheels on each axle. Similar to Bucyrus-Erie, LeTourneau, and Gar Wood scrapers, the Terra Clipper’s ejector cable was routed over the center of the bowl to a sheave on top of the ejector, which used a roll-out ejection system instead of forced ejection by a tailgate.
During World War II, Wooldridge continued building blades, rippers and scrapers for the military, and started designing a motor scraper. Its first motor scraper, the Terra Cobra Model TCY, was introduced in 1945; “TC” stood for the Terra Cobra tractor, and “Y” was for the scraper. Like the Terra Clipper scrapers, the Terra Cobras were cable operated. The first models used a three-drum system with air controls, but later models had an air-controlled two-drum system. The Terra Cobras also had a unique steering system that used two hydraulic cylinders running along each sideframe of the tractor. A multi-strand roller chain ran from the cylinders back and around a swing circle below and concentric with the scraper’s kingpin. Instead of a steering wheel, Terra Cobras used a horizontal bar with short handles at each end, much like those used on the early Caterpillar crawlers. Turning the bar to the left or right moved the cylinder in that direction. Until the mid-1950s, all Terra Cobras used Cummins engines, and Cummins powered some models into the 1960s. Rated at 14 yds. struck and 18 yds. heaped, the TCY had four forward speeds and was powered by a six-cylinder, 150 hp engine. It was upgraded to the TC-S14 in 1948 and the TC-S142, with 225 hp and a 10-speed transmission, in 1950.
It was also around this time that the Morrison-Knudsen Company, Inc., of Boise, Idaho, acquired a financial interest in Wooldridge. M-K, part of the Six Companies joint venture that built Hoover Dam and other major projects, had grown to become one of the largest contractors in the western U.S. During the 1940s and 1950s, M-K purchased large numbers of scrapers and other equipment from Wooldridge. M-K had 34 Wooldridge pull scrapers and nine Terra Cobra motor scrapers on one Missouri River levee job, and for the Union Pacific Railroad’s third main line over Sherman Hill from Cheyenne to Dale, Wyo., M-K used eight 17-yard Terra Clippers and five 15-yard Terra Cobras in 1952 to 1953.
Wooldridge also offered a 20-yard dump wagon called the Cobra Wagon (later, the Cobra Haul) for the Terra Cobra tractor that could be easily interchanged with the scraper unit. Rather than having hinged doors on the bottom, the dump body was bottomless and rested on a steel plate with rails on either side. To drop its load, the body was pulled by cable along the rails toward the rear beyond the steel plate. Later models included standard rear dump wagons as well. Meanwhile, the pull scraper line evolved into two series: the larger Terra Clippers (18-30 yds. heaped) and the Boiling Bowls (7.5-14.2 yds.). Boiling Bowl scrapers had floors that curved upward toward the rear to create a boiling action of the excavated material to maximize each load and used a two-drum cable control system while the Terra Clippers used a three-drum system. Other products offered during the post-war years included three pull ripper models, and blades and cable control units for larger tractors from Allis-Chalmers, Caterpillar, and International Harvester. Brisk sales moved the company to open a sales office in Chicago in the early 1950s.
In 1952, Wooldridge revamped its pull scraper line into the Open Bowl series. These scrapers featured cable reeving through the sides of the bowls and were designated with an OS followed by two or three digits. It included six models with heaped capacities from 10.5 yards to the 41 yard OS300, which was considerably larger than anything else on the market. Wooldridge had entered into a manufacturing agreement with Mississippi Road Services (MRS) in 1955 to provide OS-series pull scrapers, including the OS-300, for its wheel tractors. The scrapers built for MRS were modified by the addition of rear-wheel brakes and a hydraulic load transfer cylinder placed between the yoke of the scraper and the rear of the tractor. Wooldridge also entered into manufacturing agreements with J.D. Adams Company to build scrapers and, in 1951, with Mack Trucks to build LR and LV off-highway trucks at its Sunnyvale plant. Like many other equipment manufacturers, Wooldridge changed the color of its machines from orange to yellow. It also dropped rippers and bulldozer blades from its product line.
During this time, Wooldridge sued Caterpillar Tractor Company and the U.S. government, alleging that a large contract for tractors and scrapers had been wrongfully awarded to Cat due to proper procedure not being followed. The Comptroller General ruled in Wooldridge’s favor, and ordered the contract cancelled. However, by that time over ninety percent of the order had been completed, and Caterpillar was paid for that amount. The case went to the U.S. Court of Appeals, which ruled in favor of the government.
In 1955, Wooldridge became a division of the Continental Copper and Steel Industries, Inc., and Harold Gusman became a vice president of Continental. The following year, the Wooldridge Division expanded its motor scraper line to four models: TH-0142 (225 hp, 18 yds. heaped); TH-090B (180 hp, 15 yds.); the Cobra Quad, a three-axle unit (300 hp, 26 yards); and the small Cobrette (143 hp from a GM 4-71 engine, 10 yds.). Like the former TC models, “TH” indicated the tractor and the numbers applied to the scraper. Bottom- and rear-dump wagons were offered for the TH models and the Cobra Quad. All motor scrapers received a new steering system called a Roto-Gear; the Roto-Gear had twin hydraulic motors that applied torque to a bull gear on the scraper’s yoke to make turns.
Curtiss-Wright Corporation (CW) of South Bend, Ind., purchased the Wooldridge Division in 1958. Formed in 1929 by the merger of companies founded by the Wright Brothers and Glenn Curtiss, CW was trying to diversify itself from being solely dependent on the aeronautical business. It had taken over the Studebaker Corporation in 1956 and had spare manufacturing capacity at the South Bend automaker’s factories. It also dedicated 400 acres at the South Bend facility for a proving ground for scrapers. CW continued offering the six pull scraper models, four motor scrapers, and three bottom dump models from Wooldridge, with new model number prefixes: CW for motor scrapers, CWT for pull scrapers, and CWD for bottom dumps. In 1959, it added two larger motor scraper models to the line: CW-220 (27 yards, 375 hp) and CW-226 (36 yards, 375 hp); both got new grille and hood styling.
In 1960, the pull scraper line was pared to two models, CWT-8 and CWT-30, and continued slow sales forced further reductions in its entire scraper line. Big problems for CW were that all of its scrapers were cable-operated while most of its competitors were converting to hydraulic controls, and it did not offer a full line of construction equipment, which helped keep buyers loyal to a particular brand. CW ended scraper production in 1961, and the last gasp of the scraper line was a contract to provide CWT18M 18-yard struck/26-yard heaped cable-controlled pull scrapers for the U.S. Army in 1963 for use with Caterpillar 830M and Michigan 290M wheel dozers. CW is still in business, but is no longer involved in construction equipment manufacturing.
This article was reprinted with the permission of the Historical Construction Equipment Association from the Spring 2011 Issue of Equipment Echoes.