Editing Caterpillar D9 (section)

==Engineering and technical description==
{{More citations needed section|date=August 2024}}
The D9 is a series of heavy tracked-type tractors, carried on [[continuous track]]s and usually used as [[bulldozer]]s. The series began in 1954 with a prototype tractor called the D9X. Ten D9X prototype models were built in 1954. In 1955, the {{convert|286|hp|abbr=on}} D9 was introduced to compete against the more powerful [[Euclid Trucks|Euclid TC-12]]. The D9 came equipped with a 1,473 [[Cubic inch displacement|cid]] D353, which powered the D9 until the 1980 introduction of the D9L. In 1956, the D9 had its engine power raised to {{convert|320|hp|abbr=on}}. The new {{convert|335|hp|abbr=on}} D9E replaced that model in 1959. Two years later, the legendary {{convert|385|hp|abbr=on}} D9G was introduced; it remained in production for 13 years; it became the main crawler on many job sites, testifying to its sturdiness and design.

In 1965, West Coast businessman Buster Peterson hooked up a pair of D9Gs to pushload the largest wheel tractor scrapers built. In 1968, Caterpillar bought the rights to this concept, thus the {{convert|770|hp|abbr=on}} DD9G was created (DD stands for Dual D9G).<ref>{{cite web |last1=Berry |first1=Thomas |title=The Dual D9 |url=https://www.oemoffhighway.com/home/article/20858662/the-quad-d9 |website=OEM Off Highway |date=18 April 2017 |access-date=2020-01-02}}</ref> Peterson also built the first SxS D9G, which has two D9Gs side-by-side, pushing a {{convert|24|ft|m|adj=on}}-wide bulldozer blade.

In 1969, Caterpillar introduced this new SxS D9G. In 1974, the improved {{convert|410|hp|abbr=on}} D9H was introduced to replace the D9G. The D9H is still the most powerful conventional track-type tractor in company history. The DD9H and the SxS D9H soon followed.

In 1980, the {{convert|460|hp|abbr=on}} D9L was introduced. The unit featured the same new type of [[Caterpillar D10#High Drive system|elevated drive sprocket]] undercarriage as had been introduced on the larger [[Caterpillar D10|D10]] in 1977.{{efn-lr|The D10, and the elevated sprocket drive, was developed over several years from 1973 before its commercial debut.}} The new undercarriage design reduced strain and shock loads on the final drives<ref>{{cite web|last=Caterpillar Inc|title=D9R Track-Type Tractor|url=http://www.albahar.com/assets/products/Product%20Machines/D9R.pdf|access-date=15 November 2012|archive-date=18 April 2013|archive-url=https://web.archive.org/web/20130418133432/http://www.albahar.com/assets/products/Product%20Machines/D9R.pdf|url-status=dead}}</ref> and gave the "belly pan" more ground clearance. The elevated-drive-sprocket undercarriage is a modular design. To repair the machines, one breaks down the tracks and pulls the drive sprockets out. As a result, one can pull the powershift transmission out of the rear.

The D9L was replaced by the {{convert|520|hp|abbr=on}} D10N in 1987. The {{convert|370|hp|abbr=on}} D9N replaced D8L in 1987 (this was due to a model number/size adjustment by Caterpillar in their larger bulldozer lineup at the time, allowing them to introduce a smaller D8N model below the larger D8L size). Due to the model adjustment, the D9L is the most powerful D9 in history, with a flywheel power of {{convert|460|hp|abbr=on}}. The D9L is also the heaviest D9 in history at {{convert|130,000|lb}}.

In 1988, Caterpillar produced their 25,000th elevated-drive-sprocket track-type tractor, a D9N. The {{convert|405|hp|abbr=on}} D9R replaced the D9N in 1996. The {{convert|410|hp|abbr=on}} D9T replaced the D9R in 2004. The main difference between the D9T and the D9R is the installment of the new [[Cat C18 ACERT]] inline-six engine in the D9T vs the V8 3408 HEUI in the D9R. The D9R has clutch and brake steering, while the D9T has differential steering. The D9T has a low-emissions ACERT diesel engine. The current model is the D9 (no letter); however, older models such as the D9T, D9R, D9N, and D9L are still commonly used. The L, N, R, and T models of the D9 are visually very similar, differing primarily in the design of their internal systems.