14 April 2000



This is said to be the last hydrostatic drive tractor to leave the IH production line at Doncaster when production ceased in 1985.

When International

Harvester stopped making

tractors with hydrostatic

drive they left a gap in

the market which other

manufacturers have ignored.

Mike Williams reports

HYDROSTATIC transmissions are still popular for equipment ranging from 5hp lawn tractors to some of the most powerful combine harvesters, but they have not been available on ordinary mid-range tractors since International Harvester built the last of their 95 Series Hydro models at their Doncaster factory in 1985.

The attractions of a hydrostatic transmission include simplicity. Instead of using a gearbox with intermeshing cogs, the engine of a hydro tractor powers a piston pump to force oil through a motor to drive the wheels. This has helped to give hydrostatic drives their reputation for reliability, and they are also easy to operate with no gears for a novice driver to crunch.

On the IH Hydro tractors the clutch pedal is used only for starting the engine or as an inching pedal, eliminating clutch wear problems, and instead of changing gear to alter the travel speed, Hydro drivers can simply slide the hand operated control lever for infinitely variable adjustment of the travel speed without altering the engine or pto speeds.

Forwards/reverse changes are equally easy. Moving the control lever forwards or backwards selects the travel direction – without using the clutch pedal – and moving the lever to the neutral position stops the tractor.

The main disadvantage of hydro drive is increased power loss compared with a gearbox, which would reduce its efficiency for jobs such as ploughing.

Modern development

Transmission development has moved a long way since the early 1980s when Hydro tractors were rolling off the IH production line. The latest powershifts with electronics and shuttle controls have caught up with or overtaken most of the features offered by hydrostatic drive, but this has been achieved at the cost of additional complexity, weight and cost, and Julian Brown says many farmers would welcome a modern replacement for the old IH tractors.

Julian runs the 174 ha (430-acre) Hopton Farm at Hopton near Bury St Edmunds, Suffolk in a family partnership with his father Alan and brother Andrew, and their tractors include two IH Hydro models. The older of the two is a 21-year-old 77hp Hydro 84, and the other is the improved 85 version, also with a 77hp engine.

The order for the 85 was placed when Alan Brown heard the news that hydrostatic models were to be axed from the IH tractor range, and he was told that his tractor was the last one to be built in 1985.

The Hydro 84 model with 6000 hours on the clock is used mainly for loader work, and this is one of the jobs which particularly suits hydrostatic drive, says Julian Brown.

"You dont alter the engine revs, and you control the speed and direction with one lever. It is quick and easy, and of course you dont get expensive clutch problems," he says. "I should think it would take me 10 minutes less to put up a load of bales with this tractor than with a gear drive tractor of similar age."

The Hydro 85, with about 3000 recorded hours, is used mainly for drilling and hoeing sugar beet, both jobs requiring precise control at slow speeds, and it also powers the Browns round baler. Baling is another job which normally demands plenty of clutch pedal work, especially on a baler which has to be reversed for each bale drop, but on the Hydro 85 the transmission control lever does it all.

Hedge cutting

"We do our hedge cutting with a Hydro tractor, and we also used one on the potato harvester. The harvester we are using now is beyond the capacity of the Hydro tractors, but it is the sort of job a hydrostatic drive does really well. It allows you to vary the forward speed to suit the crop condition, but the engine speed and the pto remain constant, and thats exactly what you need," says Julian Brown.

The Browns enthusiasm for hydrostatic transmissions is also evident on some of the other equipment at Hopton Farm. The same type of transmission is on the Bobcat loader used for handling muck from the beef unit, fertiliser, and loading sugar beet, the Bonser forklift in their potato store is an elderly hydrostatic drive model, and their combine is an Axial Flow 1450 with hydrostatic drive.

Julian thinks there is still a gap in the market for a tractor to replace the old IH Hydro models. The original Hydros fell from favour, he says, because IH seemed to lose interest in promoting or developing them, and they became a victim of the rationalisation and cost-cutting which followed the Case takeover of IH.

"The Hydro tractors needed some improvements which IH never dealt with. One problem is that the transmission has only two ranges, and a third range would be a big improvement," he says. "But both tractors have performed very well, and the reliability has been excellent.

"I think there would be a demand for a hydrostatic tractor to replace the IH Hydro models. Its still a very good transmission for jobs such as loader work, and it would probably be less expensive than some of the transmissions they use on modern tractors." &#42

Julian Brown thinks a modern Hydrostatic drive tractor would fill a gap in the market.

The Hydro 85 decal on the Brown familys hydrostatic drive tractor.

The list of hydrostatic drive equipment includes this Bonser

forklift truck.