Up to the 1980s our front axles were mainly non-driven, but, starting in the 1970s, driven front axles came to be more in demand. This was due to better pulling ability, better stopping ability and more control over trailed equipment on steep ground in a 4WD! Some 2WD tractor drivers have been heard to comment that, although being pushed to the bottom of the field by a heavy silage trailer behind a trailed forage harvester was a frightening experience, it was preferable to spending half a day replacing power-shaftjoints after the harvester overtook the 4WD tractor down the same field. David Browns 2WD front axle consisted of a centre beam mounted to the main frame front extension by a trunnion pin that allowed for articulation over uneven ground, and beam extensions slid into the centre beam to give variable track widths.
These would locate on a taper and were held in place by two bolts; however, if the top face of the extensions touched the underside of the centre beam the point of location then relied solely on bolts that could potentially break off. Welding shims to the sides of the beam extensions was found to cure this problem.
Due to loader tractors being increasingly used to transport heavy bales of silage, the front axles of 990, 995 and 996 tractors started to look a little poorly after a period of use. It was possible to fit the heavier axle from 1200 series tractors but greasing the axles was also found to keep them in good order longer. On greasing the kingpins, grease may only be emitted at the bottom; the top bush can be helped to get grease by drilling a 1/16in diameter hole horizontally in the large washer which retains the steering lever, this prevents an airlock being formed at the top of the kingpin. Of course the old solidified grease may need cleaning out first.
In 1970 the 990 and 1200 tractors were offered with front-wheel drive using an axle manufactured by the Italian firm Selene; however, road speeds on these tractors was relatively slow as they were fitted with 9:50 rear reductions. In 1976 a German front-drive axle, manufactured by Krammer, was fitted and the final drive ratio was increased to 10:49, thus bringing the 4WD 1210 into line with the 2WD tractors. The Krammer axle had higher ground clearance so the rear reductions were turned to bring the tractor level.
In 1978 4WD once again became available on the 990, and also on the 996, but this axle was of David Brown manufacture and made at Leigh. In certain overseas markets the 4WD 996 models were also available with the Italian Carraro front axle. This axle gave the tractor a more level appearance due to the drive being a straight shaft from the transfer box to the front differential, whereas the aforementioned axles all had two universal joints in the prop
shaft. The Carraro axle eventually became the only front-drive axle to be fitted on David Brown tractors. It had a limited slip front differential, the universal joints in the hubs were protected from external damage, and it appeared to be fixed to the front extension in a more robust manner, although lack of greasing to the bearing caps could lead to a loose axle clue to wear. Oil leaks from the hubs could also be a problem, but a wear sleeve can be manufactured locally and pressed onto the turned hubs if you experience such a problem.
Another 4WD tractor produced at Meltham was known as the ’Vegetable Special’ it was based on a 1394 and fitted with four equal sized 12x38 wheels. The rear reductions were turned to level the tractor and the front axle was a Carraro fitted with a different ratio, modified hubs and a strengthened track rod. A Carraro epicyclic reduction was also fitted in the transmission to give creeper speeds for row crop work, providing 15 forward speeds. This tractor was primarily built for the American market in areas of vegetable production, mainly Southern California where good ground clearance and the ability to work in irrigated land to get produce from the field and to the customer was important. A small number were, however, also supplied to Holland and Spain.