Wooldridge is not a name many of our readers will be familiar with and yet it was an important evolutionary branch of the motor scraper ‘tree’. RICHARD CAMPBELL EXPLAINS.
Mack Wooldridge (1890-1962) was a contemporary of Robert LeTourneau and was trained as an auto mechanic. He was fascinated by heavy equipment and was one of the pioneers in attaching a workable bulldozer blade to a track type tractor.
He became a Cletrac tractor dealer and designed many attachments for these crawler tractors, which were adopted by the parent company.
As his experience and success increased he also began designing and building attachments for Allis-Chalmers, International and Caterpillar track type tractors.
In 1927, Wooldridge set up his own company, Mack Wooldridge Inc. in Sunnyvale, California and was building bulldozer blades, angle blades rippers, cable control units and the first of his BB range of towed scrapers. The BB was short for ‘boiling bowl’, which well described the loading action of his scrapers
By the mid 1930s Wooldridge was a serious competitor to LeTourneau, LaPlant-Choate and Bucyrus-Erie for tractor attachments and he opened an office in Birmingham, Alabama to widen the sales scope of his products and cover the east coast of the US.
Although a US west coast-based company, Wooldridge products were sold throughout the United States, Canada and Mexico and were exported to Australia and South America with a couple of the towed scrapers even making it as far as New Zealand.
During WWII Wooldridge built attachments for the US military – mainly bulldozer blades.
Inspired by the success of LeTourneau’s Tournapull motor scrapers, Wooldridge began designing one of his own, and by late 1945 the machine was put into limited production (war time restrictions permitting) as the Wooldridge model TC-Y ‘Terra-Cobra’.
This was the third true overhung type motor scraper offered by any US manufacturer (the others being LeTourneau and LaPlant-Choate).
The TC-Y could not be called an attractive machine by any means but it carried a very useful 18 cubic yard payload and was faster than any of the competition.
TC-Y Terra Cobras were used on several high profile jobs of the 1940s including a huge earth fill dam in Fort Peck, Montana and the realignment on many miles of the Northern Pacific Railroad in North Dakota and were popular in the Pennsylvania coalfields stripping overburden.
Wooldridge (now known as Wooldridge Manufacturing) undertook a redesign of the TC-Y in 1948 that resulted in the model TC-S.
The principal difference between the two machines was in refinements built into the scraper bowl, which on the TC-Y had the draft arms pivoted on the back axle and on the TC-S saw the pivot removed to a point about halfway along the bowl sides. This made for easier push loading which, on the earlier TC-Y, would often see the rear wheels lift clear off the ground due to the geometry involved.
The model TC-S remained in production until 1956 when it was replaced by the TH series (TH-090, TH-090B and TH-110). These were reasonably attractive looking machines compared to the earlier TC-Y and TC-S and were a considerable improvement on the former models.
Also new to the TH series machines was a two, rather than three-drum cable control unit.
Wooldridge also tried to compete in the three-axle high speed scraper market with a machine they called the T4-200 ‘Cobra-Quad’. Equipped with a 330 horsepower GM 6-110 diesel and carrying a 27 cubic yard bowl, the Cobra-Quad was ideal for fast long haul earthmoving on jobsites with minimal gradients. It was also available with a 20 ton capacity rear dump.
Smallest and, as it turned out, last in the Wooldridge motor scraper range was the model T-70 ‘Cobrette’. This was a seven cubic yard machine powered with a 138 horsepower GM 4-71 diesel and aimed squarely at the utility and small contractor end of the market.
Wooldridge also designed and manufactured the scraper bowls for M-R-S (Mississippi Road Supply) in a variety of sizes some of which were huge.
Most of M-R-S’ sales were to the US military but they also sold to the private sector as well. This manufacturing agreement ended in 1958.
In June 1958 the Curtiss-Wright Corporation (of aircraft fame) bought the Wooldridge manufacturing Co for US$5 million and shifted operations from California to South Bend, Indiana.
Curtiss-Wright continued to build the Wooldridge motor scraper and towed scraper range, suitably re-badged Curtiss-Wright, until 1961 when it exited the earthmoving business entirely. The decision to quit was based on the huge capital cost of redesigning new competitive product as the exiting designs were by now quite dated and still all cable operated when all of the competition had moved on to hydraulics.
Curtiss-Wright, which was fairly cash strapped at the time, simply did not have the capital to invest in research and development.
So Wooldridge disappeared completely from sight and largely from memory.
Today, references to the Wooldridge company and its history are very hard to find. Its literature is even rarer and some of the published information available is inaccurate. This is a pity as, in its day, Wooldridge was an innovative company and deserve a little better recognition than it has received.
Wooldrige: Mechanics and innovations
Right from the start Wooldridge preferred to use Cummins diesels for itsTerra-Cobras, not venturing away from them until the late 1950s when it broadened its horizons and began to utilise GM diesels as well.
Wooldridge steering systems were unique to the motor scraper industry. Models TC-Y and TC-S were hydraulically steered, but not in the accepted fashion but rather by two cylinders, one on either side of the tractor, connected by a length of roller chain which wrapped around a sprocket on the scrapers 11-inch-diameter kingpin.
If that wasn’t quite enough, all the subsequent machines employed ‘Roto-Gear’ steering, which employed two rotary hydraulic motors geared to the vertical kingpin and providing constant torque through any turn.
Final drives weren’t immune to Wooldridge’s technical innovations either and all Wooldridge motor scrapers and their Curtiss-Wright brethren, apart from the T-70 Cobrette, employed spur gear/roller chain final drives.
Ejection of the load was done by roll-out (similar to Euclid) rather than by a dozer type ejector. Early TC-Y, TC-S and TC-S142 machines had quite complex overhead reeving of the scrapers cables that was not satisfactorily cleaned up until the TH series appeared.
A nice feature also unique to Wooldridge was the spring cushioned push block which allowed push tractors to contact the scraper “on the go” without sending the operator through the windshield.
In a time when mechanical controls meant just that, Wooldridge utilised air-assisted controls to operate their scraper functions and a simple T-bar handle as a steering wheel.
While aesthetically Wooldridge scrapers would never win any beauty contests, at least they were functional.
The New Zealand connection
Apart from a couple of towed scraper imports, I can find no evidence of any Wooldridge motor scrapers coming into New Zealand. There were however, two Curtiss-Wright machines imported, a CW-28 and a CW-215, both delivered to NZ Roadmakers.
The bowl section of the CW-28 still exists as a towed scraper conversion.
For the model collector
Good luck – I have never seen any scale models of Wooldridge motor scrapers in any scale. However, during the late 1940s the Doepke company produced a 1/16th pressed steel toy of a never-produced Wooldridge bottom dump (based on the TC-Y tractor) and the Marx-Lumar company did likewise to 1/24th scale. These toys, although not entirely accurate, are quite collectable.
The only other model of a Wooldridge machine is that issued by Matchbox to 1/76th scale in the 1960s and represents a Cobra-Quad with rear dump. It is however painted in Curtiss-Wright colours and marketed as a CWD-321.
Brief specifications – First of the line – the TC-Y
Manufactured from: 1945 to 1948
Engine: Cummins HRB600 6-cylinder diesel rated at 225 horsepower at 1800 rpm
Clutch: 17” single plate Lipe-Rollway dry type
Transmission: Fuller 4A112, 4-speed manual
Final Drives: Spur gear and roller chain
Brakes: Air operated expanding shoe type
Tyres: 24.00×25, 24-ply
Top speed: 18 mph
Steering: Hydraulically actuated roller chain
Turning circle: 23’ 3”
Capacity: 14.2 cubic yards struck, 18 cubic yards heaped
Length: 35’ 10.5”
Width: 11’ 6”
Height: 10’ 11”
Operating Weight: 24.5 tons (empty), 49 tons (loaded)