The Caterpillar D8

A true classic tractor in every sense of the word, the Caterpillar D8 has been around in various forms since 1935.   BY RICHARD CAMPBELL

This segment of the Caterpillar D8 story features only the conventional drive tractors, that is, non hi-drive machines (RD8 thru D8K).

Cat_D8_7.jpgDeveloped from Caterpillar’s successful model Diesel 75, the original D8 machines were known as RD8s (the ‘RD’ designation was dropped halfway through production) and carried the series number 1H.

Powered by a 115 horsepower six-cylinder naturally aspirated Caterpillar model D13000 diesel engine they weighed approximately 16.5 tons (depending on equipment) and had a six-speed manual transmission.

Bulldozer blades and other operating equipment was normally supplied by outside manufacturers such as LeTourneau or LaPlant-Choate, Caterpillar’s preferred suppliers.

According to Caterpillar records, just under 10,000 of the 1H series were manufactured up until 1941 when the 8R series replaced it.

The D8 (8R series) was manufactured throughout WWII and thousands were supplied to the US armed forces.

Engine horsepower of the D13000 was increased to 132 and the weight rose to 17 tons. Attachments were still sourced through LeTourneau and LaPlant-Choate.

Cat_D8_6.jpgQuite a few of these machines ended up in New Zealand following WWII and can be identified as ex-military machines by the figures “US7” stamped into the serial number plate above the machine’s serial number. This designates US Navy 7th fleet, which operated in the Pacific area.

Immediately following the war Caterpillar introduced a new version of the D8, the 2U series, which sported several refinements over its predecessors and of course, more horsepower – 144 at the flywheel.  

During its lengthy production life this particular version of the D8 saw numerous improvements and upgrades as the   

type was developed, most notable of which was a new five-speed transmission the replacement of the standard dry type clutch with Caterpillar’s famous oil clutch which extended service life of this critical component by a considerable margin.

With the introduction of the 2U series Caterpillar also started to supply its own blades and attachments, although other brands could still be specified at the buyers request.

Cat_D8_5.jpgA fully equipped D8-2U weighed approximately 18 tons.

The 2U series was a major seller, with Caterpillar delivering over 23,500 examples.

Following the 2U came the 13A series, the last of the D13000 powered D8s.

Looking very much like its 2U predecessor apart from a larger fuel tank, the 13A series production run lasted from 1953 to 1955 and was not built in very large quantities.

As such, the D8-13A is considered to be an interim type.

The D8E, D8F and D8G

In 1955 two all-new D8s, with a brand new engine, were introduced.

These were the D342 powered D8E and D8F (14A series) manual transmission with oil clutch (the ‘E’ became an ‘F’ when oil-cooled steering, clutches and brakes were introduced) and the D8G (15A series) manual transmission with torque converter drive.

Producing 191 horsepower, the D342 diesel was a naturally aspirated six-cylinder inline engine that had been specifically designed for the new D8. No other piece of Caterpillar mobile equipment used the D342 engine.

Both transmission options featured a forward/reverse lever (first introduced on the 2U series) to cut down on the number of gear changes an operator had to perform during a shift.

Attachment options were now all supplied by Caterpillar and the operating weight had risen to 20 tons.

Big seller, the D8H

Cat_D8_2.jpgThe next major revision to the D8 design came in 1959 with the introduction of the 225 horsepower model D8H

The horsepower increase was gained by turbo-charging, and Caterpillar subsequently tweaked this further, very early in the production run, to 235 horsepower. However several other improvements, notably to the operators area and the sheer size of the machine, were apparent.

It was available in three versions – the 35A series torque converter drive, 36A direct drive and 46A series with powershift transmission.

By far and away the most popular of these was the 46A series with over 33,000 examples being produced.

Cat_D8_3.jpgSeveral versions of the D8H were manufactured by Caterpillar’s UK facility, where it was known variously as the 22A, 52A and 68A series.

This marked the first time variants of the D8 had been constructed outside of the USA.

Another horsepower revision was made around 1965, from 235 to 270 horsepower, and this is where the previously ultra-reliable D8 started to suffer problems in the engine department.

Despite Caterpillar’s best efforts, the problems were never entirely corrected even in the last production version the D8K.

A fully equipped (blade and ripper) D8H tipped the scales at 25 tons.

Last of the old line, the D8K

Cat_D8_1.jpgThe D8K, introduced in 1974, was the final production model of the conventional drive D8 track type tractor series, and this saw yet another increase in engine horsepower which was raised to 300.

Featuring improvements to the hydraulic system and a completely revamped operator’s environment, the D8K was produced in both direct drive (76V series) and powershift transmission (77V series) versions. The powershift version was also concurrently manufactured in the UK as the 66V series.

A spacer plate was added between the engine block and cylinder heads in an attempt to alleviate a liner dropping problem, but, realistically, the D342 was now at the limit of its designed capabilities.

A stylishly designed full ROPS cab was offered as an option and this could be tilted back to allow access for major servicing.

Fully equipped a D8K weighed almost 30 tons and was a vastly different animal to that which had first rolled off the Peoria production line in 1935.

The last D8K was manufactured in 1982 and replaced by the new hi-drive D8L.

The New Zealand connection

Cat_D8_4.jpgLiterally hundreds of D8s have been imported into the country by New Zealand franchise holder Gough, Gough & Hamer and through private importation.

One of the early arrivals took part in the famous crushing of a Public Works Department wheelbarrow and shovel by then Minister or Works Bob Semple in 1936.

Since then Caterpillar D8s have participated in all manner of works throughout New Zealand including logging, quarrying, mining, hydro and civil earthworks.

Although it is now rare to see one of the pre-war machines in operation, there are still some about which have been preserved.

A list of New Zealand D8 owners would just about fill this magazine, and would include all major contacting companies past and present.

From an operator’s perspective

Your writer has been on a lot of D8s in his time, in fact the only types he hasn’t operated have been a 1H and a 13A series.

They are good honest work tools with a great lugging engine and make excellent blade, ripping, towing or push tractors.

For the modeller

There are some models available of the Caterpillar D8 although most are not cheap.

Arpra (Brazil) make a nice model of the D8K in 1:50 scale with an angle blade but it is a little hard to find and can be quite expensive.

Ertl (USA) make a very nice 1:25 scale kitset of a later production D8H with 8S blade and radial arc ripper. If you’re good with your hands this is a model worth adding to the collection. It is generally available thru on-line auction sites such as ebay.

Conrad (Germany) has issued excellent models of the RD8 and a D8-2U in 1:25 scale but both are very hard to find and therefore are horrendously expensive. 


Contractor Vol.33  No.11  December 2009 - January 2010
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