CaterpillarOff-Highway Trucks

The Caterpillar 769 series

The Caterpillar 769 was Caterpillar’s first serious foray into the world of off-highway trucks and faced a lot of long-established competitors, but proved itself to be a very worthy machine over its production life. By Richard Campbell.

When Caterpillar first introduced its model 769 off-highway truck in 1963, it caused quite a stir within the earthmoving and quarrying industries.  Caterpillar was very well known for its track type tractors but off-highway trucks were a very radical departure from the norm. In fact, development had been underway for a number of years, as Caterpillar had correctly perceived that there was an opportunity in this market for a modern off-highway truck that was superior to what was currently available.

At that time, by far the biggest manufacturer and market leader of off-highway trucks was GM’s Euclid division, followed by LeTourneau-Westinghouse, International-Harvester, Dart, Isco and Mack.  Apart from LeTourneau-Westinghouse, all the other manufacturers used a time-honoured design of a heavy ‘I-beam’ ladder type mainframe with conventional leaf spring suspension. LeTourneau’s design differed somewhat in that its chassis had a large structural ‘horsecollar’ for torsional flexibility and had introduced nitrogen over oil suspension struts, which LeTourneau-Westinghouse called “Hydrair Suspension”. Before too long, all sizeable off highway trucks would use a form of this suspension. Caterpillar also decided to use oil suspension struts on its 769 from the very start although its chassis design was of a slightly more conventional nature.

The nominal body capacity of the 769 was 35 tons, (around 23.5 cubic yards), which made it an ideal sized truck for most applications apart from big opencast mines. It was constructed of high strength steel, and featured a 3-section tapered floor. Exhaust heating of the body was standard, the exhaust exiting through a notch on the right-hand rear of the body. Power was provided by the popular and reliable Caterpillar D343T 6-cylinder, turbocharged diesel engine rated at 400 flywheel horsepower. Users could choose between direct electric starting, or the use of a 2-cylinder petrol starting engine, similar to those which had been in use on Caterpillar track tractors for years.

The transmission was a full powershift type with three distinct ranges giving the 769 a possibility of 9-forward speeds. This powershift transmission was very similar to that already fitted in Caterpillar’s new 600-series motor scrapers which had been introduced a year earlier. Overall, the powertrain combination gave the new 769 a top speed of 43 miles per hour, making it a real mover.  In another innovative move, Caterpillar fitted oil cooled disc brakes on the rear axle to slow the machine down in place of the usual air operated shoe brakes. Caterpillar did offer shoe brakes, but only as a factory fitted option on the front steering axle and they were not fitted as standard equipment.

New thinking was all over the 769 and this included the operators cab which was made of fiberglass.  The idea behind this was to cut down on the resonance normally associated with other brands of off-highway truck, and to make the cab easily repairable should it get damaged.  In service, this cab gave all sorts of problems and while reasonably quiet, was subject to cracking. However, the first version of the 769 proved to be quite popular and was manufactured from 1963 to 1967 when it was replaced by the 769B.

The 769B.

Probably the most popular variant produced, the 769B was first introduced in 1967 and addressed a lot of the problems that had surfaced with the original 769 variant.  Engine output was increased slightly by 15 horsepower to 415 flywheel horsepower, but there were three major changes from the original design which were immediately apparent.  First was the cab which was now made of steel, second was the dump body which was completely redesigned and now featured a ‘V-floor’ (capacity remained the same), and third was the method of entry to the cab.  On the initial production version, the operator boarded from the rear of the cab while on the 769B, he got into the cab via a ladder on the left front of the machine. Formerly an option, brakes were now fitted as standard on the front axles as well as the rear.

In service, 769Bs could be found everywhere, and they were a very popular machine, even spawning a tractor only version known as the 768B, designed to haul bottom dump trailers which were manufactured for Caterpillar by Athey Products Corp.  The 769B was in continuous production from 1967 to 1978 when it was replaced by the 769C.

The 769C.

A total redesign, the 769C was a 769 in name only as the machine featured a completely new front platform and cab, a new engine and transmission, plus an all-new dump body.  Still rated at 35-ton capacity, the 769C was first introduced in 1978 and was powered by a Caterpillar 3408 V-8 diesel putting out 450 flywheel horsepower.  Connected to the engine was a new 7-speed electronically controlled powershift transmission. This combination gave the 769C a slightly higher top speed than previous variants, up to 47 mph.  The dump body, while still having a V-floor, was now wider and shallower making for an easier target for shovel and loader operators. In order to simplify the machines manufacture, Caterpillar had gone to a lot more angular construction, doing away with a lot of the rounded curves of the previous two models.

The 769D.

The 769D was the final production version of the 769 and was first introduced in 1995. Rather than a new machine, the 769D could really be looked upon as a ‘fine-tuning’ of the previous 769C.  Externally the 769D resembled the 769C quite closely apart from its dump body which had now done away with external box type stiffeners and featured lengthwise stringers on the side sheets instead.

Power was again increased by the installation of a Caterpillar 3408E V-8 engine which had an output of 485 flywheel horsepower, making the 769D the most powerful of all the 769 series. The transmission remained the same.  The 769D was in production from 1995 to 2007 when the 769 series was replaced by the model 770, a 38 ton capacity off-highway truck.

The New Zealand connection.

Caterpillar 769s from the 769B onwards have seen widespread use in New Zealand and many are still in use.  They have continued to be reliable workhorses for those that own them and have racked up impressive operating hours, being used on almost all of the major hydroelectric projects in this country following Benmore.

For the model collector.

It makes a refreshing change to advise that all 4 versions of the Caterpillar 769 are available in model form, and all are to 1:50 scale.   The original 1963 version of the 769 (we’ll call it the 769A) has been made by Classic Construction Models (CCM) but is a bit of a collector’s piece and now hard to find, (not to mention expensive).  Two manufacturers have produced models of the 769B, Gescha/Conrad and CCM, but the CCM version is vastly superior.   Unfortunately, it is hard to find and again, expensive.   Both the 769C and 769D have been manufactured by NZG and are good, if somewhat basic representations of the type.    With a little bit of extra detail, they make good additions to any 1:50 collection and are much easier to find than either the 769A or 769B.

Brief specifications – first production Caterpillar 769 (1963)

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

Transmission:             Caterpillar barrel type planetary powershift, 9F/1R

Top Speed:                  43 miles per hour

Brakes:                        Oil cooled disc brakes on rear, optional air/shoe on front axle

Steering:                      Full hydraulic, with twin steering cylinders

Turn Circle:                54’ 8”

Std.Tyres:                   18.00×25, 32-ply, E3

Capacity:                     35 tons

Loading Height:          10’ 1”

Length:                        25’ 1”

Width:                         11’ 9”

Height:                         13’ 4”

Operating Weight:      25 tons (empty), 56.2 tons (loaded)

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