Classic Machines

The Caterpillar 633 elevating scraper

The 1960s and 1970s were a very fertile time for machinery manufacturers with a worldwide boom in earthmoving projects, and the big manufacturers of the day did not want to be left out of the sales opportunities. By Richard Campbell.

These two decades also saw a great deal of experimentation with various machine types – particularly motor scrapers.

From small beginnings in the 1950s (led by Hancock and Johnson), the elevating scraper began its rise in popularity with most manufacturers introducing a model, or two, and the trend was for progressively larger machines of this type.

Caterpillar, not wanting to be left behind in the market for this type of machine, had previously offered a 16 and a half cubic yard elevating scraper, the J619, utilising the tractor unit of its 619C open bowl scraper mated to an elevating scraper bowl designed and built by Johnson Manufacturing of Lubbock, Texas. (Caterpillar eventually acquired a portion of Johnson).

This machine had a relatively short production run as Caterpillar introduced a new version of the machine called the 621 with an entirely new tractor unit and engine.

The elevating scraper version of this machine was known as the J621.

Caterpillar’s competitors kept coming out with larger elevating scrapers, so it decided to “bite the bullet” and build a large elevating scraper and the model 633 was the result.

Powered by a 400 flywheel horsepower Caterpillar D343T six-cylinder diesel engine and utilising the job-proven 631B tractor unit with an all-new 32 cubic yard bowl assembly designed and built by Johnson Manufacturing, the first of these new large elevating scrapers was known as the 633. Following field testing, it was put into production in 1966 as the model 633 (44J series).

Caterpillar’s cushion hitch suspension system was not available for the original version of the 633 but it featured an ejection system that is still unique among elevating scrapers today. The entire bowl floor assembly tilted at a central pivot point to distribute the load, with the leading edge of the bowl floor serving as a strike-off plate for levelling.

Initially, sales of the 633 were quite modest in comparison to that of its rivals (Caterpillars customers no doubt getting used to the idea of a big Cat elevating scraper and that really strange floor mechanism).

The original model of the Caterpillar 633 was in production from 1966 through to 1970.

When Caterpillar replaced its 631B open bowl scraper with the updated 631C model in 1969, the 633 elevating scraper also received the new tractor unit, this combination being known as the Caterpillar 633C (66M series).

While cubic capacity remained the same at 32 cubic yards, the horsepower of the D343T engine was boosted to 415 flywheel horsepower (from 400), and the new 633C also featured Caterpillar’s cushion hitch as an option, and the new eight-speed Caterpillar semi-automatic powershift transmission that made the 633C not nearly as sluggish as its predecessor.

The 633C proved to be a far better machine and it cemented Caterpillar’s position as a viable contender in the 30 cubic yard elevating scraper market with good unit sales numbers.

Remaining in production until 1975, the 633C was replaced by the all-new 633D (25W series) featuring a completely redesigned tractor unit and a brand new engine –  the Caterpillar 3408 V8, which was rated at 450 flywheel horsepower.

The Cat 633D was the real deal, a beast of a machine with ample power and capacity and the operators loved it too!

Such was its success that Caterpillar developed it further by adding an extra engine in the rear to create the twin-powered model 639D.

The Caterpillar 633D was the last of the 633 series to use the original tilting floor ejection mechanism.

The next development of the 633 series was the 633E (1AB series) which appeared in 1992.

This version of the machine had an all-new 34-cubic yard capacity elevating scraper with a sliding floor ejector, bringing it in to line with all of its major competitors (and potentially making it more commercially ‘acceptable’ to users in my opinion).

Engine output of the Cat 3408 V8 was increased, now up to 475-flywheel horsepower, and a completely redesigned operators’ compartment was installed in the fixed ROPS cab.

The Caterpillar 633E was in production for four years, 1992-1996 when it underwent a further upgrade.

When the updated 633E series II was introduced in mid-1996, all of Caterpillar’s competitors in this size scraper class had vanished!

This was due to a worldwide downturn in the sale of large motor scrapers of all types, and competitors deciding it was not worth the investment in capital to produce improved or new elevating scrapers.

The 633E series II (2PS series) was powered by an improved version of the Caterpillar 3408 V8 diesel, the 3408E that produced 490-flywheel horsepower, making this the most powerful of all the 633 series machines.

Lasting in production until the year 2000, the 633E series II was the last iteration of this model that Caterpillar has manufactured, and it has not been superseded by an equivalent or subsequent version.

Caterpillar 633 in New Zealand

It appears that the Caterpillar 633 was just too big or specialised a piece of equipment for local contractors’ applications, as I cannot find any record of any being imported here. For that matter, none of its similar sized single engine competitors made it to our shores either

There is however, an example of the 633’s larger, twin-engine sibling, the 639D at Hatuma Lime Co, but the nearest Caterpillar 633’s can only be found in Australia.

 For the model collector

 There have been currently two models of the Caterpillar 633 made, both 633D versions and both were made by CCM (Classic Construction Models).

Easiest to find is the 1:50 scale version that is a little miniature masterpiece complete with a functioning cushion hitch, opening ROPS cab door, tilting bowl floor mechanism and non-functional elevator. There were only 300 of these produced.

The other is to 1:87th (HO) scale and was a very limited offering made of brass!

It is/was very expensive and, of course, being a limited production item is quite hard to find as well. Good luck tracking either of these down.

Original 1966 production Caterpillar 633 Specifications


Engine:  Caterpillar D343T, 6-cylinder, turbocharged & aftercooled diesel rated at 400 flywheel horsepower @ 1900 rpm

Transmission:             Caterpillar 9-speed full powershift, barrel type planetary.

Brakes:                        Shoe, full air, S-cam operated

Tyres:                          33.25×35, 32-ply E3

Top Speed:                  32 mph

Steering:                      Full hydraulic, 90° each way.

Turning Circle:           40’

Capacity:                     32 cubic yards

Elevator:                     Hydraulic driven by vane type motor

No.of Flights:              13

Flight Speed:              4-speeds from 150 to 300 feet per minute

Length:                        43’ 10”

Width”                        12’ 6”

Height:                        13’

Operating Weight:      40 tons (empty), 76.5 tons (loaded)

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