The Caterpillar 639D elevating scraper: an overview by Richard Campbell
The Caterpillar 639D was designed specifically to take on Wabco in the large (30 cubic yard plus) twin-engined elevating scraper market, and to this end it did a good job.

Wabco had had this portion of the earthmoving business entirely to itself since the introduction of its BT333F in the late 1960s and had been continually developing and improving on it, first with the 333FT and then the 353FT.

To be quite frank, Wabco made very good big elevating scrapers.

Caterpillar, which at this point had only ever manufactured single-engined elevating scrapers, was determined to have a slice of this action and set about designing a twin powered elevating scraper of its own.

Trials were undertaken with several prototypes at Caterpillar’s Arizona proving grounds until a satisfactory configuration was agreed upon.

The 639D as the machine came to be known, was not developed from Cat’s 637D twin powered open bowl scraper with an elevator mechanism inserted as quite a few people think, but from the lesser known 633D single engined elevating scraper.

Officially introduced in 1979, the Caterpillar 639D was a 34 cubic yard elevating scraper with 700 horsepower at its disposal, nitrogen/hydraulic cushion hitch and a top speed of some 35 miles per hour.

In the tractor unit, power came from a 450 horsepower Caterpillar 3408T V8 engine with a 250 horsepower Caterpillar 3306T inline six-cylinder diesel in the rear.

Initial sales of the new machine were good but there were storm clouds on the horizon with a global downturn in large projects looming.

Sales began to slow dramatically as the work on big jobs and opencast mine stripping dried up.

This downturn not only affected Caterpillar but all the major players in the industry and was responsible in part for the demise of International-Harvester, Fiat-Allis, Wabco and Clark-Michigan.

Sales of big scrapers, open bowl or elevating, were just not there so the decision was made to pull production of the 639D in 1984 after just five and a half years.

This should not be regarded as a bad reflection on the 639D, which was a very capable machine, but on the industry that spawned it.

Gone also was the 639D’s major rival, the Wabco 353FT, the downturn hitting Wabco so badly that it exited the scraper market entirely and sold off its earthmoving divisions to Dresser Industries.

At least Caterpillar had its other core products such as track type tractors to keep it going.

Total production of the Caterpillar 639D was not very great with less than 300 manufactured.

A high proportion of these were exported to Australia where they worked well in the sandy soils of Western Australia.

The machine was right, Caterpillar just got its timing wrong!

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