The Caterpillar 933 Traxcavator

Following the acquisition of the Trackson Corporation by Caterpillar in 1951, Caterpillar continued to use Trackson’s loader attachments fitted to D2, D4, D6 and D7 tractors.

Trackson had been founded in 1922 in Milwaukee, Wisconsin, and built a plethora of attachments for not only Caterpillar but other manufacturers as well.

However, its star offerings were pipelayers and front end loaders.

Prior to the buyout, Trackson had been working on a project where the loader was an integral part of the track-type tractor and not just an “add-on”.

While very effective, Trackson’s loaders did have their limitations and the closest that Trackson got before Caterpillar took them over was the release of the model HT4, based on a wide gauge Cat D4-7U series, which addressed a lot, but not all, of the issues inherent in the design.

It was also Trackson’s first all-hydraulic front end loader and was released in 1950.

Caterpillar knew it was on to a very good thing with the purchase of Trackson and immediately started refining some of Trackson’s ideas once the integration of the company was complete.

Caterpillar followed up Trackson’s HT4 with its own model No. 6 Shovel in 1953.

This, like the HT4, was all hydraulic and based on a contemporary D6 chassis (in this case a wide gauge D6-9U series).

It was an immediate success and spurred on further development within the loader division.

Next off the production line was the 933, after Caterpillar decided that both tracked and wheeled loaders needed their own number series (900) to differentiate them from their standard track type tractors.

Initially known as the “No. 933 series C Traxcavator”, (in deference to Trackson), the 933C was a purpose-built track type loader, not an adaptation of an existing machine.

It featured a one cubic yard bucket with integral loader frame built into the chassis making for a substantially stronger unit, and was fully hydraulic in operation.

Power came from a naturally-aspirated 50 horsepower Caterpillar D311 4-cylinder diesel which was connected via oil clutch to a 4-speed manual transmission.

The 11A series 933 series C rode on D2 undercarriage but this was found to be a little wanting in service and so at around serial number 11A2956 a change was made to D4 sized undercarriage components.

Caterpillar called this modified model the 933 series E and it was produced up until 1958 when the next variant was released.

Following the series E machine into service was the 933 series F.

This version was a little more refined than previous versions and featured a larger, 1.12 cubic yard bucket.

Early on in the production run a separate forward-reverse lever was added to the transmission which was a great benefit to the operator who, up until then, had to de-clutch, change gear and re-clutch again in order to change direction.

The only downside was that it added an extra lever to an already very cramped operating environment.

In 1965 Caterpillar determined that the 933F could use a little more horsepower so the decision was made to increase the output from 50 to 60 flywheel horsepower.

This was achieved by a change of engine rather than tweaking the fuel rack setting.

The new engine chosen was the Caterpillar D320T, a 4-cylinder turbocharged diesel recently added to its product range.

In this configuration the machine was known as the 933 series G and the D320T remained the standard powerplant right up until the time that the 933 was discontinued entirely in 1968.

At the time the machine was discontinued, it was, it has to be said, at the end of its development potential.

Due to the design of the chassis it was not practicable to fit a powershift transmission and so the 933 always remained a manual transmission machine.

Also, the narrowness of the operator’s compartment, surrounded by a multitude of levers made it a trifle dangerous to get out of should a mishap occur.

The sheer number of controls also made it a ‘fatigue magnet’ and the author is convinced that most operators were glad when the day’s shift was over.

During its lifetime the machine gained approximately one ton in weight, mostly due to the undercarriage revision that was undertaken when the machine went from a series C to a series E.

Operating weight of a late production 933G was approximately eight tons.

A replacement sized machine was not immediately forthcoming and it was left to the vastly superior (but larger) 1¼ cubic yard Caterpillar 941 to fill the gap until a replacement could be designed and built.

This did not occur until 1972 when the model 931 arrived on the scene.

For all its faults and quirks, the 933 shifted one heck of a lot of dirt in its time, and the later, turbocharged G models had a distinctive sound when operating.

These days the role of the small track-type loader has been largely taken over by the hydraulic excavator which is far more flexible in its operating envelope.

Contemporaries of the Caterpillar 933 included the Allis-Chalmers HD5G, Case 450, Komatsu D30S and International TD-6 Drott, Z100 & 100B.

The New Zealand Connection

The Caterpillar 933 was very popular in New Zealand and well over 100 of all series were imported.

Such was their versatility they were particularly popular with local & regional councils who utilised them in all manner of works.

Private sector buyers eagerly snapped up traded-in units and many small contractors owe their start in the earthmoving business to a second hand 933.

Examples of the machine today are very rare, most having gone to the big stockpile in the sky.

For the Model Collector

A very bleak outlook here as no models have ever surfaced, in any scale, of a Caterpillar 933.

For a machine that was as popular, and sold in the volume that the 933 did, it is a pity that no one has produced one.

Perhaps the folks at the Antique Caterpillar Machinery Owners Club (ACMOC) may consider one for a future release?

Brief Specifications, 42A series Caterpillar 933

Engine:  Caterpillar D320T, 4-cylinder, turbocharged diesel engine rated at 60 flywheel horsepower at 1800 rpm

Transmission: Caterpillar 4-speed manual, constant mesh.

Clutch:           Caterpillar patented Oil Clutch

Capacity:       1.12 cubic yards with standard GP bucket

Operation:    Full hydraulic

Gauge:             60”

Track Frame:   5 roller

Std.Shoe:         14”

Tracks:           35-section, sealed

Length:            14’ 2”

Width:             5’ 10”

Height:                        7’ 1”

Operating Weight: 8 tons

The Caterpillar 933 Traxcavator

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