# Slewing and rotator failure in a Liebherr LH35 – step-by-step diagnosis and repair

> Liebherr LH35 material handler: a noisy, jerking grapple rotator and oil overflowing from the slewing gearbox reservoir. Brake leak test, new slewing motor seals, new rotator motors and hydraulic oil filtration.

![Slewing and Rotator Failure in a Liebherr LH35 – Step-by-Step Diagnosis and Repair](https://wibako.com/media/articles/article-818/k99ez7-gzzi.webp)

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.

## Result

- The rotator turns smoothly and quietly.
- The oil level in the gearbox reservoir no longer rises.
- The hydraulic system has been cleaned of particles from the worn motors.

We offer [hydraulic pump and motor repairs](https://wibako.com/services/repairs-of-hydraulic-pumps-and-motors), [hydraulic oil filtration](https://wibako.com/services/hydraulic-oil-filtration) and [construction machinery service](https://wibako.com/services/construction-machinery-service).

**Watch the repair video:** [Slewing and Rotator Failure in a Liebherr LH35 – Step-by-Step Diagnosis and Repair](https://wibako.com/about-us/video/818-slewing-and-rotator-failure-in-a-liebherr-lh35-step-by-step-diagnosis-and-repair)

Published: 2026-03-20

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Source: https://wibako.com/about-us/news/819-slewing-and-rotator-failure-in-a-liebherr-lh35-step-by-step-diagnosis-and-repair
Contact: +48338704200, biuro@wibako.pl