A Liebherr LH35 material handler came to us with two problems. The first was a noisy, jerking grapple rotator – the vibration was transmitted through the whole boom and machine, especially when slewing started. The second was oil overflowing from the slewing gearbox reservoir. The video shows the diagnosis of both faults and the repair step by step.

Rotator: motors worn to the limit

The rotator drive consists of two small hydraulic motors meshing with the main gear. Before disassembly we washed the whole assembly – with components this dirty, working clean saves a lot of trouble. Once the motors were opened, the verdict was clear: pronounced steps had formed on the raceway and gears, and the surfaces were worn to sharp edges instead of being smooth. With this level of wear a rebuild makes no sense, so we fitted two new motors from our stock.

Slewing: where does the oil in the gearbox come from?

On this machine the slewing gearbox has a reservoir with minimum and maximum marks. If the gearbox shaft seal fails, the oil level drops. Here it was the opposite – the oil level kept rising and overflowing. That meant hydraulic oil was entering the gearbox from the slewing motor or the slewing brake.

Before dismantling the motor we tested the brake: we applied external pressure of about 35–36 bar (the same as in the system) and closed the valve. The pressure held, so the brake was tight and the culprit had to be the slewing motor.

Slewing motor repair

After removal we found two possible leak points: the outer O-ring and the shaft seal. The machine has over 20,000 operating hours – the shaft seal was rock-hard and the O-ring barely protruded from its groove. The shaft itself was in good condition. We still dismantled the whole motor to rule out other damage: the pistons and cylinder only needed lapping and polishing. We replaced the seals, secured the shaft seal with a circlip and assembled the rotating group with grease. After tightening the end plate we always turn the shaft with a wrench to make sure it rotates freely – once it is back in the machine it would be too late.

After refitting the motor, the gauge still showed 35 bar – confirming the brake was tight. Finally we topped up the slewing gearbox oil.

Oil filtration instead of an oil change

The customer rightly asked: if the rotator motors wore out, where did the metal particles go? Answer: into the tank and the system. The oil had recently been changed together with the pump and filters, so instead of draining it we connected a filtration unit overnight. The filtered oil can safely stay in the machine.