Technik der land- und forstwirtschaftlichen Zugmaschine - Vehicle Technology
This domain covers the checks and technical understanding a driver must have before taking a tractor on the road: brakes, tyres, steering, hydraulics, lighting and the PTO.
Brakes
- Tractors use hydraulic or compressed-air service brakes; trailers are usually two-line air braked. The red coupling head is the supply line, the yellow one the brake line - crossing them means the trailer either does not brake or brakes permanently.
- Check the air reservoir pressure before moving; the system must reach operating pressure and the low-pressure warning must go out.
- The parking brake must hold the laden combination on a gradient. If it creeps, it needs adjustment, not a bigger effort.
- Braking must be symmetrical. A tractor that pulls to one side under braking has a seized cylinder, a wet or contaminated lining or unequal adjustment - take it out of service, because asymmetric braking on a combination ends in a jack-knife.
Tyres and running gear
- Correct pressures for the load; check cold, including the trailer.
- Minimum tread depth of 1.6 mm in the main grooves; sidewall cuts, bulges and perished rubber mean immediate replacement.
- Wheel nuts and studs re-torqued after wheel changes; cracked rims and leaking valves are defects.
- Track width as wide as the work allows, for stability.
Steering, linkage and PTO
- Check steering play and hydraulic oil level; a leaking hose is a defect, not a nuisance.
- The three-point linkage and quick couplers must be locked; an implement dropping on the road is a serious accident.
- PTO guards and master shield in place; 540 and 1000 rpm shafts must never be mixed. Entanglement injuries are fatal.
- Differential lock and four-wheel drive only when needed - engaging them on dry tarmac increases wear and worsens steering.
Cab, lighting, documents
ROPS or cab intact, seat belt functional, mirrors and all lights working, beacon where required, first-aid kit and warning triangle on board, papers for tractor and trailer available.
Worked example
After winter storage the tractor pulls right when braking with a loaded trailer. Diagnosis: unequal braking force, typically a sticking wheel cylinder or oil-contaminated linings. Correct action: do not drive on the road; repair first, then re-test on a dry, empty stretch at low speed. Reasoning: braking asymmetry is magnified by trailer mass and by a high centre of gravity, turning a small pull into a loss of control.
Traps that cost marks
- Testing brakes only empty and at low load.