David Brown Hydraulic Engineering

Hydraulics was an area in which l had little personal involvement so I have enlisted the help of Trevor Williams who was in charge of Hydraulic Test at Scar Bottom in Meltham – in compiling this section. But before we go too far, we should set the scene by describing some of the improvements and differences between the Selectamatic and the Implematic hydraulic systems in a simple and understandable way. The Implematic tractors had height control, depth control and traction control, as did the new Selectamatic system. The lmplematic tractors had the lift and lower valves mounted on the pump, which were located in front of the PTO. These were operated mechanically with linkages, in height control from a cam on the ramshaft and in depth from a cable mounted on a spring loaded top link assembly. Trevor recalls that depth control was a little jerky and the cable on the top link could be vulnerable to damage. Height control was not that efficient and could cause the oil to overheat.

The Selectamatic tractors had the valves located in the right-hand side of the rear axle, and a cam on the end of the ramshaft relayed height control. A sensing unit mounted on the top of the PTO relayed, via a cable, depth control signals to a spool valve that hydraulically operated the lift or lower valves, thereby giving better control than the Implematic’s direct mechanical linkage to the lift and lower valves. A dump valve, not needed on Implematic tractors, was incorporated to lower quickly a tipped trailer or lightly loaded links. The rate of drop could also be adjusted. Taps controlled the early three-way valve but as machining accuracy improved, a spool valve was introduced and this had the added advantage of visibly showing which service was selected. The hydraulic pump on the smaller tractors was mounted in front of the PTO, but on the larger tractors this was driven directly from the front pulley on the crankshaft and mounted in the front extension. A second pump could also be mounted in this manner where extra flow was required for external equipment.

Up to three double-acting take-off valves could be mounted on the rear axle for operating double-acting rams, and some had power loaders operated from these valves. As rear-mounted equipment got larger, especially ploughs, development had to be done on the back end of the tractors. Field Test driver William Noble gradually broke ’everything’ they put on the back end of a 1200, and, on one occasion, when using a five-furrow fully-mounted Bamfords Kvernland plough the ramshaft broke and the crack was herd by Derrick Smith a couple of fields away.

The lift ram operated the ramshaft from the left-hand side of the rear axle but this tended to produce a twisting effect in the ramshaft, so a linkage support ram was fitted at the right-hand side of the axle. This meant that the tractor could now lift heavier implements, but this resulted in greater strain in other areas and the ramshaft bolts were duly upgraded from ‘s’ to ‘v’ grade.

The paper gaskets – used between the PTO case and axle, and the axle and the mainframe – were discovered to be extruding, resulting in oil leaks and a loss of bolt torque under the twisting effect produced by long heavy ploughs. Alan Earnshaw was buying sealant products in the early 1970s, and remembers that Loctite came to Meltham with a request to try a new gasket eliminator on a small number of tractors. ‘Obviously they hoped to sell it to us in large quantities, but there was a marked resistance from certain powers. Loctite were told that if they wanted to use David Brown tractors to test their products, they would have to offer considerable guarantees in case their products failed in use and caused damage to the tractors. In the end three tractors, a 995, 1200 and 1210 were built using gasket eliminator. But under heavy field-testing it was found that, where it replaced paper gaskets around the PTO, the troublesome capillary-type oil leaks were not occurring when a heavy load was placed on the back end. A decision was soon made to use the liquid gasket and eight of us from different departments were sent to the Loctite factory in Hertfordshire on a producttraining course, in order to explore other application possibilities. Later Loctite engaged a suite of rooms at a hotel in Leeds, to offer half-day familiarisation courses, and dozens of people went from Meltham to gain product knowledge, and an excellent “free” lunch as well!’

However, despite the initial promise of the eliminator, it was to be sometime before it became used on the production line and the oil leaks continued.

Indeed the oil staining often left a mess around the back end, and, along with the oil stains around the engine block, the power red paintwork took on an ugly look. Peter Williams, an industrial chemist, writes: ‘The official reason given for the change from power red to black was that the red paint contained a high element of lead. However, that could not be the case, as our paint specifications had been developed with the American market in mind. They were more acutely aware of lead contamination than we were and even in the early 1970s we were sourcing our supplies from car paint manufacturers. The new spraying area at Meltham Mills was one of the most modern in the world, and the unions also had a pretty strong outlook on employee safety. So i for one take the view that the change to black paint work was either a shadow of what was to come with the Case International colour scheme orjust a means to make the oil leaks look less obvious.’

On the 1410 and 1412 tractors a newly-designed back end was introduced, and the ram cylinder bore was increased by 1/2in to 4in. The piston stroke was over 1 1/8in longer, and this increased the maximum working load from 2,200lb on the 1212 to 2,600lb on the 1412. The ramshaft and lift arms were stronger and the lift arms had forked ends to attach to the lift

rods. Where the lift rods attached to the lower-links they could be either in the conventional fixed position or could use slotted holes to allow wider implements to float over undulating ground. Telescopic link ends were also provided to enable easier hitching of heavy implements. Hughie Cartwright first had these on his 1412, which he used with a three-furrow reversible plough and found hitching this heavy implement much easier. A later hitching aid introduced on the 90 series were detachable balls that were left on the implement, and this meant that attachment could be achieved by simply reversing the tractor on to it.

The link ends were aligned with the balls – being held at the correct centres by an adjustable bracket on the lower links – and a lever was then operated on the lower link, which in turn released a plunger that held the ball.

The top link was attached in a similar way by lowering it down on the upper ball already fitted to the implement. All this could be done without the driver leaving the tractor seat, or that was the theory. On initial trials with what we called ‘Jeffes balls’, it was found that the jaw in the lower links could open thereby losing the plough if it jumped over a rock for instance.

Initially oil filtration was achieved by a gauze and magnetic filter under the transmission and a bypass filter mounted on top of the rear axle; this was later replaced by a suction filter as well as the gauze and magnet under the transmission. Later, on the front-mounted pump tractor, a full flow pressure filter was located on the rear axle. This was a finer filter giving better protection to the hydraulic components from contaminants. With the introduction of the 1690T lower link sensing replaced top link for the first time and this introduced better depth control for longer implements especially semi-mounted ploughs. In Field Test we used to use a Kvernland seven-furrow semi-mounted plough with spring back bodies, which would have been too heavy to lift without the rear wheel, and was coupled to the tractor with the lower links only. The sensing used two leaf springs under the rear axle and a mechanical linkage to the spool valve. This system was chosen for production because Case already used leaf-springs on their tractors.

Trevor remembers experimenting with an electronically-controlled hitch system in the mid-1970s, but it would not work fast enough to get decent control. Latterly, in Field Test, three different electro-hydraulic systems were evaluated namely Bosch, Cessna and Case. The Case system used sensing pins built into the lower links, whilst the Bosch and Cessna used a sensing pin where the lower links attached to the rear axle. The Case system used a variable displacement pump of closed centre design, but Bosch and Cessna had an open centre hydraulic system like the Selectamatic. These three systems were under assessment for the 96 series, which was being developed for manufacture at Meltham but this never happened and the range was eventually built in Germany.

VAK 1

(1939-1945)

VTK1 / VIG1

(1941-1949)

VAK 1A

(1945-1947)

VAK1C

(1947-1954)

Tracklayers

(1942-1963)

Taskmaster

(1948-1965)

VAD6 50D

(1953-1959)

900 Series

(1955-1957)

VAD12 2D

(1956-1961)

950 Series

(1958-1961)

850 Series

(1961-1965)

880 Series

(1961-1965)

990 Series

(1961-1968)