Modern crawlers are so universally associated with dozer blades and dirt work that it's hard to imagine that their fundamental design was born of a prime-moving need for more flotation and traction on the farm. Indeed, when Holt Mfg. Co. released the first successful gasoline-powered crawler in 1908, the tractor was designed specifically to work California's rich Sacramento River delta, and its duties were all about pull. Although this tractor had some reliability difficulties, its successes were significant enough to net Holt nearly 200 competitors within less than a decade. When the dust from bankruptcies and consolidation settled in 1920, only about 10 manufacturers remained in business. By decade's end, that number was halved, which made room for one more player - International Harvester Co.
Exactly why IH didn't claim a share of the tracklayer market early on is anyone's guess, but most Harvester historians point to complex patent issues relating to crawler undercarriage design, and the company's intense focus on wheeled tractors. Market size also played a role in the decision-making process, since crawler tractor production rarely amounted to more than 10 percent of wheeled tractor counterparts. However, International Harvester engineers were well aware of advantages associated with endless-track drive systems long before the company entered the crawler market, and had worked with them as early as 1916 or 1917.
A slow crawl
Early IH documents point to an experimental drive-train program centered on the 4-cylinder International 8-16 wheeled tractor (not to be confused with the 1-cylinder 8-16 Mogul), which included skid-steer-style four-wheel and six-wheel drive variants along with a pair of tracklayers. At least two experimental 8-16 crawlers were built in the late teens. One was a half-track concept steered with front wheels; the other had full tracks and steering clutches. In these experimental designs, Harvester's track was notably light-duty and the 8-16 project was never developed further, but tracks appeared on other experimental machines in upcoming years.
Crawler tractor development at IH ground to a halt in the early 1920s, but that didn't deter allied equipment companies from taking a stab at it. By 1924, several approved manufacturers offered track kits to fit Harvester's McCormick-Deering 10-20 and 15-30 standard tread tractors. For example, Hadfield-Penfield Steel Co. offered the Alwatrac full crawler attachment for the 10-20 that included the necessary steering system in addition to the undercarriage, while Moon Track of Los Angeles and San Diego offered a half-track attachment that replaced the tractor's rear drive wheels with a pair of crawlers, leaving the front wheels to handle directional changes. Tracklayer conversions could also be obtained from Mandt-Freil, Trackson and others.
Encouraged by the successes its tractors achieved with aftermarket crawler makers, Harvester engineers pursued their own conversion design and announced the McCormick-Deering 10-20 and 15-30 Track Layers in mid-1928. These machines offered 10 and 15 respective drawbar horsepower and are extremely rare today (particularly the 15-30 version). Most so-called Track Layers appear to have been prototypes for the 10-20 (and possibly 15-30) TracTracTor (note the name change), which entered regular production on Oct. 1, 1928. Little documentation exists for the 15-30 TracTracTor beyond 1929, but the 10-20 version proved popular enough to survive.
Harvester continued to modify the 10-20 TracTracTor with steady improvements to the undercarriage, final drives and steering clutches. On Aug. 15, 1930, it was renamed the No. 20 TracTracTor to more closely match nomenclature used by competitive models such as the Holt 20. This last of Harvester's converted wheeled tractors was replaced in 1931 with a more purpose-built tracklayer. Production estimates based on monthly serial number data suggest that no more than 486 10-20 TracTracTors were built between Oct. 1, 1928 and May 1, 1930. Using the same measure, no more than 954 of the No. 20 TracTracTors crawled off the assembly line from Aug. 15, 1930 to June 1, 1931.
Crawling up to speed
As with virtually all wheeled tractor conversions, Harvester's own attempts with the 10-20 and 15-30 proved cumbersome and underpowered. These machines did, however, stimulate development of a more purpose-designed farm crawler that, according to Harvester memos, was "built from the ground up." In corporate documents dating to 1930, the new TracTracTor was referred to as the Model 15 and in others the T-15, but by the time it hit regular production in July 1931, Harvester's first true crawler tractor was called the T-20 TracTracTor.
The 7,000-pound, 24.44 maximal drawbar horsepower T-20 featured IH's 3.75-by-5-inch bore-and-stroke, 4-cylinder valve-in-head kerosene/gasoline engine and a 3-speed forward (one reverse) sliding spur-gear agricultural transmission. Power from the transmission was fed to left and right pinion and bull-gear final drives through a pair of dry-type steering clutches. The standard 41.51-inch gauge track frame featured three heavy-duty bottom rollers and a single top idler in addition to the equal-diameter rear drive sprocket and front idler. A 51-inch gauge (50-inch in some references) track frame was also available.
The T-20 was joined by the larger and heavier (about 11,000 pounds) allfuel TA-40 TracTracTor in March 1932. This machine initially offered nearly 43 maximal drawbar horsepower with its 3.625-by-4.5-inch bore-and-stroke, 6-cylinder kerosene/gasoline engine. That number increased to 45.58 horsepower (burning gasoline) when the engine's bore was increased to 3.75-inch in 1936 and the machine was renamed the T-40. Power from the engine was fed through a 5-speed, close-ratio sliding spur-gear transmission to the pinion and bull gear-type final drives. Steering was accomplished with a pair of single-disc dry clutches and brakes. The big farm crawler featured a heavy-duty 47.75-inch gauge track frame with five bottom rollers and two top idlers. A 60-inch gauge track was optional.
In 1933, the TA-40 was joined by the 43 maximal drawbar horsepower diesel-powered TD-40 TracTracTor, which featured the first American-made engine that started on spark-ignited gasoline, switching over to compression-ignited diesel fuel once warmed. The TD-40's innovative 4.75-by-6.5-inch bore-and-stroke, 4-cylinder engine added about 700 pounds to the crawler (compared with the TA-40), which was equipped like its kerosene- or gasoline-burning siblings in virtually every other way.
Bolstered by the early successes of their first two purpose-built farm crawlers, Harvester engineers developed a pair of intermediate-sized machines released in 1936 as the T-35 and TD-35 TracTracTors. According to company memos, these machines were "skinned-down versions of 40-series crawlers" designed specifically to meet competitive power and price points for tracklayers intended solely for agricultural use. The 35-series TracTracTors had about 38 maximal drawbar hp and were mounted on smaller and lighter track frames than the 40-series machines.
The T-35 was powered with the same 6-cylinder gasoline engine found in the TA-40 tractors, while the TD-35's engine was a 6.5-inch bore version of the 4-cylinder diesel used in the TD-40. Both 35-series crawlers were available with 45- or 56-inch gauge track frames featuring four bottom rollers and a pair of top idlers. The 35-series TracTracTors also had a close ratio 4-speed transmission in a drive-train design very similar to Harvester's other crawlers.
Although IH designed its TracTracTor family of crawlers for drawbar work with farming as the principal focus, all of the machines eventually found their way into industrial and heavy construction markets. When used as prime movers, the tractors performed well, but when equipped with dozer blades and loaders, substantial modifications to the undercarriage were required to avoid seriously shortening their service life. Even then numerous steering clutch and final drive failures were reported.
As IH was actively marketing the 35-series TracTracTors, engineers were well into the design of their replacements along with an even larger machine specifically built for industrial duties code-named the TD-65.
The massive TD-65 concept was released in October 1938 in time for the 1939 model year as the TD-18 TracTracTor. Although designed principally for heavy construction projects, this 72-plus-drawbar horsepower machine found work on large western farms pulling hardpan-shattering rippers and was used extensively in soil conservation and land clearing. Although this largest of all TracTracTors symbolized IH's new focus on industrial tracklayers, it was shortly joined by a series of similarly-styled new farm crawlers that effectively replaced the 20-, 30- and 40-series machines.
For model year 1940, the T-20 was replaced with the gasoline T-6 and diesel TD-6 TracTracTors, each with about 30 hp at the drawbar in packages that weighed about the same as the T-20. The larger and heavier T-9 and TD-9 TracTracTors weighed less than the 35-series tractors but offered the TD-40's power. All four of these machines featured completely new undercarriages, drive and steering systems, and engines. Like their predecessors, the 6- and 9-series TracTracTors were designed expressly for agricultural drawbar and PTO work, but they were also fitted with integral mounting points to facilitate use with blade and loader attachments.
The T-6 TracTracTor was powered with IH's C-248 3.875-by-5.25-inch bore-and-stroke, 4-cylinder engine set up to burn either gasoline or distillate, while the TD-6 used the similarly dimensioned D-248 gas-start diesel. All 6-series crawlers featured 5-speed close-ratio transmissions, conventional clutch and brake steering, and could be mounted on either 40- or 50-inch gauge track frames with four bottom rollers and a single top idler on each side. Nine-series TracTracTors were powered with C-335 (gasoline) or D-335 (start-on-gas diesel) 4.40-by-5.5-inch bore-and-stroke engines and equipped similarly to 6-series models, although they were mounted on 44- or 60-inch gauge track frames with four bottom rollers and two top idlers on each side.
Harvester also introduced a new medium-sized diesel-powered TracTracTor called the TD-14 in 1940 as a scaled-down version of the TD-18. This new TracTracTor was powered with IH's D-461 4-cylinder start-on-gas diesel engine with 4.75-by-6.5-inch respective bore and stroke. The machine weighed more than 17,000 pounds, was rated with about 52 maximal drawbar horsepower and generated almost 8,000 pounds of pull in ideal soil conditions. The TD-14 TracTracTor proved popular on larger farms and smaller construction sites around the world, and came standard with a 56-inch gauge (74-inch was optional) track frame with five bottom rollers and two top idlers on each side. A similarly equipped gasoline-burning T-14 came on line in 1941, but most of its very low production was earmarked for the U.S. military and it was discontinued in 1944.
This "new" farm crawler line-up remained in production through 1948, by which time all machines had been put to use (and experienced considerable abuse) in road construction, excavation, quarrying and logging. Harvester's foray into farm crawler markets was far from over, but in the late 1940s, their focus had definitely changed. Second generation 6-series, 9-series and 14-series crawlers were released in 1949 notably lacking the TracTracTor name. Although they could still be outfitted for the farm, they were now really industrial machines that were suited to agricultural work; subsequent updates pulled them even further into non-farm markets.
Back to the farm
In 1959, IH released several lightweight crawlers to fill the void left in the farm crawler market, as the TD-6, TD-9 and TD-15 (the TD-14's replacement) became fully evolved construction-type machines. This group included the 20 drawbar hp category Model T-4, and the 30 drawbar hp category Models T-5, TD-5, T-340 and TD-340. Anticipating their desirability as small industrial dozers and loaders, construction-ready 5-series machines were also offered as the TC-5 and TDC-5. Likewise, the 340-series machines could be fitted with heavy-duty undercarriage, fully reversing transmission and sufficient armor to convert them for dirt work.
The T-4 was powered with IH's 4-cylinder 3.125-by-4-inch bore-and-stroke, C-123 gasoline engine, which was well proven in many IH farm tractor models dating to the Farmall Super A. The T-5 and T-340 were powered with IH's 4-cylinder 3.25-by-4.0625-inch bore-and-stroke, C-135 gasoline engine originally found in the company's 330 and 340 wheel tractors. The TD-5 made use of IH's British-built BD-144 4-cylinder diesel engine, while the TD-340 used the D-166.
The 4- and 5-series crawlers shared a chassis that could be mounted on track frames with several gauges and lengths depending on application. In the standard configuration the 4-, 5- and 340-series machines had a 5-speed sliding spur-gear type agricultural transmission, which, when coupled with IH's proprietary 2-speed torque amplifier attachment, offered a total of 10 forward speeds. All of the machines were steered with conventional dry-type steering clutches and brakes and featured the time-proven but dated pinion and bull-gear final drives.
By 1965 when these last true IH farm crawlers were dropped from production, they offered little advantage for farmers over the day's highly efficient wheeled tractors. They also fell short in the brutal world of industrial machinery where planetary final drives and powershift transmissions had become the norm. For the next many years, only a very few IH crawlers could be special-ordered without dozer or loader equipment and with close-ratio transmissions suitable for farm duty. By the time IH sold its entire crawler line to Dresser Industries in November 1982, little evidence remained to suggest that the broad lineup of tracklayers was born on the farm. FC
Oscar "Hank" Will III is the Editor-in-Cheif of GRIT magazine. contact him at firstname.lastname@example.org