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The importance of the David Brown 780 tractor, cannot be underestimated. In 1967, the 40hp -50hp sector of both the domestic and export tractor markets accounted for the largest portion of global tractor sales. The world’s number one selling tractor, was the Perkins-powered 45.5hp Massey Ferguson 135, and David Brown needed a tractor which could compete with it head-on.
Much like its Perkins-powered nemesis, the heart and soul of the David Brown 780 was its 46hp three-cylinder direct-injection diesel engine. Referred to as the David Brown AD3/55 engine, this naturally-aspirated unit had a capacity of 2.7-litres, featured a five main bearing crankshaft with a 4.5-inch (114mm) stroke, a cross-flow cylinder head, and a vertically-mounted distributor type (DPA) fuel- injection pump.
It was September 1964 when David Brown first introduced the AD3 engine, which replaced the four-cylinder power unit used in the popular DB 880 Implematic tractor.
With more power and greater torque, the new engine gave the DB 880 a new lease of life.
Renowned for being economical, extremely reliable and almost indestructible
At the time of its introduction, the AD3 was the first engine to dispense with the wet cylinder-liners used in other David Brown engines, introducing integral cylinder bores, machined directly into the cylinder block. The benefit of this, was that not only were the bores truer, but cylinder wear was actually reduced.
Early production
In early 1965, the 2.4-litre AD3/49 three-cylinder engine was introduced in the 36hp David Brown 770 model. This engine retained the 2.7-litre engines 100mm bore, but used a different crankshaft to provide a four-inch (101mm) stroke.
For the record, the DB 770 was the first tractor built by David Brown to feature the new single-lever Selectamatic hydraulic system. This would remain a key component of the manufacturer’s products, until tractor production ceased at Meltham Mills in March 1988.
Early production examples of the DB 770, initially adopted the company’s Hunting Pink livery with yellow wheels. However shortly afterwards in October 1965, David Brown restyled its tractors introducing a new Orchid white and chocolate brown colour-scheme for what was now called the Selectamatic range. Subsequently, early production 770 Selectamatic tractors are now very rare and highly collectible.
The DB 780 was conceived by fitting the chassis of the DB 770 tractor, with the larger 46hp engine used in both the 880 Implematic and (post-1965) 880 Selectamatic tractors.
The new model came as standard equipped with Selectamatic hydraulics and David Brown’s LiveDrive system, featuring a two-stage sequential-type foot clutch, which integrated both engine-drive and PTO operation.
The standard gearbox was a David Brown two-range six-speed unit, however a four-range 12-speed unit was available as an option.
The tractor also came as standard, with 540 and 1000 PTO speeds.
Almost 12,200 David Brown 780 tractors were produced, before production ceased in 1971.
Interestingly, in terms of their popularity, both the DB 780 and the DB 770 tractors sold in almost identical numbers.
As for the engine, the smaller AD3/49 engine disappeared with the DB 770 tractor in 1970.
Yet the larger AD3/55 unit soldiered on until 1984, continuing service in the DB 885 and 1190 tractors before making its swansong in the (49hp) Case-IH 1194. Renowned for being economical, extremely reliable and almost indestructible, the AD3/55 is widely regarded as one of the best tractor engines produced by David Brown.
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