30 June 1995

Out with the old MB-Trac

By Peter Hill

FARMERS and contractors with ageing MB-trac-based self-propelled sprayers will soon be able to buy a replacement.

Humberside Mercedes-Benz dealer South Cave Tractors has developed a forward-control conversion for a specially-engineered version of the Unimog U1600. The resulting vehicle has a number of specification advances over the MB-trac-based machines, notably all-round suspension, failsafe four-wheel steering, a bigger engine and tougher transmission.

The project has become a joint venture between South Cave Tractors and the Mercedes-Benz Unimog division. "We liked the idea but wanted to see it developed under our supervision," says Derek Owen of Mercedes-Benz. "Now, we can supply a factory-engineered Unimog chassis for this application, with two-year warranty."

South Caves main interest was to make up for some of the sales lost when MB-trac production ended. "We wanted something to fill the gap," says South Caves Simon Legard. "The forward-control MB-trac conversions which have been carried out in the past are getting old and owners want to replace them. We saw that as an opportunity."

He says reliability and robust build are the main attributes of the MB-trac-based vehicles, together with front-end suspension which improves the ride to some extent, and the operator-preferred mechanical transmission – rather than hydrostatic drive. But the Unimog U1600 chassis offers a whole lot more.

"Whereas the tractor-based machines have engines of 95hp to 120hp, the new one starts out with 156hp," Mr Legard points out. "The MB-trac had some synchromesh problems but this one has a gearbox which takes 240hp in other applications and the axles have up to 6t load capacity as opposed to 4t."

The axles have the same stud fixings and are the same width as those on the MB-trac, so existing wheel equipment can be used, and there are differential locks in both front and rear axles. The Unimog chassis also comes with coil and damper suspension all round, which should give ride and boom control advantages. Assister springs are available if needed to help carry a big spray tank and boom. The main change to the Unimog chassis is the four-wheel-steering system developed so front and rear wheels track each other. Some converted MB-tracs have four-wheel-steering using modified front axles on the back. But the new machine has a Mercedes-engineered system with selectable two- and four-wheel-steering for road and field use.

The design is said to be failsafe in that if the system is not manually locked out using the electrical control it will progressively line-up, lock-out hydraulically, then lock-out mechanically as speed increases to give more controllable two-wheel-steering.

Conversion into a self-propelled sprayer involves re-routing the steering linkage – mechanical steering with power assistance to the front wheels is kept but it is hydrostatic to the rear axle – and building on a support frame for the new cab over the front wheels.

"We have kept the look of the MB-trac cab but the new design is 51cm (2in) wider to give a little more elbow room," explains Mr Legard. "Instrumentation and other fittings come from the Unimog."

The high-level technical input from Mercedes-Benz means forward-control spec Unimog U1600 chassis will be supplied from the factory complete with a two-year warranty to cover all items in the first year and engine/driveline components in the second.

Simon Legard says the vehicle will not be cheap – about £51,000 as a two-wheel-steer chassis-cab. Four-wheel-steer will add about £8000. &#42