Caterpillar D4

The Caterpillar D4 track-type tractor is a small bulldozer manufactured by Caterpillar Inc.

Caterpillar first introduced the RD4 in 1936,^[1] as the diesel follow on to the successful CAT 30 gas model. The RD4 originally weighed in at 10,000 pounds (4,500 kg), and used Caterpillar's D4400 engine, an inline four-cylinders, with a 4.25 by 5.50 inches (108 mm × 140 mm) bore and stroke.^[2] In 1935 Caterpillar had started the naming convention of "RD" for diesel or "R" for regular gasoline, followed by a number to indicate the relative engine size.^[3] In 1937, the "R" was dropped, and just a "D" was used for the diesel versions. At the time of introduction of the RD4, the D4400 engine produced about 43 horsepower (32 kW) at the drawbar so the 4 indicated the relative engine power. The D4 U series was fitted with the more powerful D315 engine. The later D4 series engines quickly increased in power, so the number "4" just became a figure of merit rather than indicating actual engine power.

• 6U = Narrow gauge 44 in (1,100 mm)
• 7U = Wide Gauge 60 in (1,500 mm)
• Caterpillar RD4 - 1936-37 (4G) with 4-cylinder D4400 engine^[4]
• Caterpillar D4 - 1937-39 (4G) with 4-cylinder D4400 engine
• Caterpillar D4 - 1939-43 (7J) with 4-cylinder D4400 engine
• Caterpillar D4 - 1943-45 (2T) with 4-cylinder D4400 engine
• Caterpillar D4 - 1945-47 (5T) with 4-cylinder D4400 engine
• Caterpillar D4 - 1947-59 6U1 > 6U12781, 7U1-7U44307 Cat 4-cylinder D315 engine.^[5]
• Caterpillar D4C - 1959-63^[6]
• Caterpillar D4D - 1963-77^[6]
• Caterpillar D4E - 1977-84^[6]
• Caterpillar D4H - 1985-96^[6]
• Caterpillar D4C SII -1990-93^[6]
• Caterpillar D4C SIII - 1993^[6]

The Caterpillar D4 was used as the base tractor for the Trackson built loader that was known as the T4 or Traxcavator shovel.^[6]

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• Caterpillar D3
• Caterpillar D2
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