When released in 1955, the Caterpillar D9D was one of the world’s largest and heaviest track type tractors, only exceeded in size by the Euclid TC-12. By Richard Campbell
Following the end of WWII and at the request of many contractors who were basically happy with their D8s but needed something larger, Caterpillar began experimenting and testing of several large prototype track type tractors and the D9 was the end result.
Other manufacturers had also been experimenting with larger tractors, notably Allis-Chalmers with its HD19 and International Harvester with the TD-24. Both rival companies had machines into the marketplace by 1947 but Caterpillar was looking at something even bigger.
The first D9 prototypes had naturally aspirated engines which were adaptations of the existing Cat D13000 diesel. However, as testing progressed it was realised that an all new engine would be required, so the designers returned to the drawing board
In order to get the horsepower needed within the size constraints dictated by the size of the tractor chassis a turbocharged configuration was chosen. The end result was the model D353 diesel engine, the first turbocharged diesel engine to be employed in a Caterpillar track type tractor.
Pre-production machines – dubbed the D9X – went into a variety of projects during 1954 for on the job evaluation, with the type going into full production as the D9 series D in 1955.
As the machines went into service, changes were made to accommodate on-going engineering improvements in the design, a necessary part of the machines evolution. Most of these changes related to internal components but externally the most noticeable visual change was from single to dual air cleaners.
The Caterpillar D9D was very popular and proved to be an effective and profitable earthmoving tool, becoming the standard on most large earthmoving and mining jobs where a large, powerful bulldozer was required.
The D series D9s were replaced in production by the E series in 1959.
The D9 described
D9 series D tractors included the direct drive 18A and torque converter drive 19A series. Production of both 18A and 19A models exceeded 4300 units combined.
We will examine a D9D 18A series, the most common New Zealand variant.
As mentioned earlier, a new engine was developed to power the D9 and this was the Caterpillar model D353TA, a six-cylinder, 6.25 x 8 inch displacement turbocharged diesel rated initially at 286 horsepower. This was increased to 320 horsepower in the second year of production commencing at machine 18A1065.
Starting method for all early D9s was the familiar two cylinder Caterpillar manufactured “pony motor” rather than direct electric starting.
This starting engine turned the main engine over against compression.
When you were satisfied that all pressures were in the green zone all it took was to open the main engines throttle and away you went.
However, I have never met any two Caterpillar pony motors which behaved in the same manner, all having various idiosyncrasies which made life interesting at times.
A direct drive transmission was utilised with a forward and reverse lever to cut down on gear shifting, the whole assembly being actuated by Caterpillar patented oil clutch.
Steering clutches were of the multiple disc type, power boosted and the steering brakes were air cooled and had their own separate blower for air pressurization.
A 90 inch gauge machine, the standard D9D rode on a seven roller track frame with two carrier rollers.
Track tension was hydraulically adjusted via a grease gun and most D9Ds were supplied on single grouser 27 inch track shoes which were considered to be the standard shoe for this size tractor.
The operator had a very clean and open space in which to perform his duties.
Placed to the left of the machine he sat in a well cushioned suspension seat (a first for Caterpillar track type tractors) and visibility was very good in all directions and aided by the tapered bonnet.
The rear of the fuel tank was tapered sharply down to aid in observing rear mounted equipment, such as a winch, ripper or a towed scraper.
All the operating controls fell within easy reach including the starting engine controls.
A comprehensive set of instruments was provided to keep an eye on what was happening internally.
A good range of extra gear was made available to outfit the D9 for purchasers’ requirements.
These included a fully enclosed cab with heater, wipers, fixed or swinging drawbar, sun canopy, logging sweeps plus sprocket and track guarding packages.
Caterpillar produced a good range of implements to compliment the D9 series D and these included the models 9S (straight), 9A (angle), 9U (universal) and, latterly, the 9C (cushion) bulldozer blades plus the No.9 radial arc ripper.
All first generation D9s have cable operated blades utilising either the No.30 (front mounted) single drum or No.25 (rear mounted), double drum cable controls. Hydraulically operated blades weren’t offered as an option until the arrival of the D9E in 1959.
Other equipment options included rippers manufactured by Ateco or CRC-Kelly and, of course, the ubiquitous Hyster D9D logging winch.
Caterpillar also offered the No.90 21 cubic yard cable operated scraper. This was later replaced by the slightly larger No.491 scraper rated at 27 cubic yards.
The New Zealand connection
Gough Gough & Hamer, the New Zealand Caterpillar distributor, delivered the first D9D to W.Stevenson & Son in 1955 for use at its opencast coal mining operation at Kopuku in the Waikato. Stevensons eventually owned eight of the D series D9s, in both 18A and 19A series.
Several others were also imported but W.Stevenson & Son was by far the largest user of the type.
The occasional D9D can still be found working, some 50-plus years after the type was first introduced.
For the modeller – Early D9s
Apart from a rather ancient Matchbox Models offering to 1:87 (HO) scale, and a very rare and expensive item from Spot-On to approximately the same scale, there is only one other model of an early Caterpillar D9 which has been produced. This is manufactured by First Gear to 1:25th scale and is of exceptional quality.
Equipped with a fully operable 9S cable blade and No.30 front cable control, the model is very accurately detailed right down to the instruments and tools in the toolbox. A reproduction of the original Caterpillar brochure is included with the model and only 2500 were produced.
Unfortunately, these limited edition, museum quality models come at a price and you can expect to pay over NZ$700 for an example if you can find one, Ebay’s online auctions being your best bet.
Hopefully some manufacturer will see the light and produce one at 1:50 scale in the near future.
Brief specifications – Caterpillar D9D (mid-production)
Engine: Caterpillar D353TA six-clinder turbocharged diesel rated at 320 horsepower
Transmission: Caterpillar direct drive, four-speed
Clutch: Caterpillar oil-type
Steering: Combination multiple disc and contracting band brakes
Track frame: Seven roller
Std Track Shoe: 27”
Length: 14’ (bare)
Width: 9’ (bare’)
Height: 8’ (to top of stack)
Weight: 29 tons (bare), up to 37 tons fully equipped