A lifting contractor in Singapore was pre-rigging an 800-tonne-class Liebherr LTM 1750-9.1 for a 680-tonne lift at a petrochemical plant. During the outrigger extension pre-check, a site engineer noticed asymmetric settlement at one outrigger pad — the outrigger was penetrating the prepared mat at a different rate than the other three positions. Investigation found the outrigger beam rubber buffer on that corner had disintegrated, allowing metal-to-metal contact that was transferring vibration into the mat surface, causing localized compaction. The lift was postponed two hours while the buffer was replaced. The cost of the rubber buffer: $180. The cost of postponing an 800-tonne lift with a 60-person crew: considerably more.
Mobile cranes — all-terrain (AT) cranes, rough-terrain (RT) cranes, and truck-mounted cranes — carry rubber components in roles far more critical than most equipment operators appreciate. From outrigger system isolation that protects lifted loads from vibration, to superstructure slewing ring mounting that must support hundreds of tonnes, rubber parts in these machines have safety implications that few other equipment categories match.
This guide covers rubber parts for the three major mobile crane manufacturers: Liebherr (LTM series), Tadano (ATF and GR series), and Manitowoc Grove (GMK series). We cover outrigger systems, carbody and superstructure mounting, cab isolation, and powertrain components.
Babacan Group supplies crane rubber components with documented traceability for critical lifting applications. Request a quote for your crane model and application.
Outrigger System Rubber Components
The outrigger system is the mobile crane’s connection to the ground during lifts. Four outrigger beams extend from the crane carrier, each deploying a vertical cylinder that bears the crane load through an outrigger float (pad) on the ground. Rubber components throughout this system affect both crane safety and lift quality.
Outrigger Float Rubber Pads
Outrigger floats are typically steel plates that sit on prepared crane mats or pads. Between the float and the mat surface, many riggers use rubber crane pads (outrigger pads with rubber bases) to:
- Distribute the point load over a larger mat area, reducing bearing pressure
- Prevent float from skating on smooth surfaces
- Provide a degree of conformance to irregular mat surfaces
These pads are not the structural rubber components of the crane itself — they are site consumables. However, the rubber pads inside the outrigger beam and cylinder connection points are structural crane components:
- Outrigger cylinder end cushions: Absorb the impact when the outrigger cylinder contacts its stroke limit
- Beam guide bushings: Line the carbody slots through which the outrigger beams slide; rubber or polymer-lined bushings reduce wear and seal against contamination
Outrigger Beam Rubber Buffers
At the end of each outrigger beam travel, rubber buffers stop the beam extension and absorb the kinetic energy of the rapidly moving heavy beam:
- Buffer load capacity: Must absorb the beam kinetic energy at maximum extension speed (typically 0.3-0.5 m/s for a 2,000 kg beam = significant kinetic energy)
- Compound: NR or polyurethane; must maintain compliance at temperatures from -30°C to +70°C
- Service life: Often overlooked; recommended inspection at each annual service
Carbody and Superstructure Mounting
The crane superstructure (boom, winches, operator cab, counterweight) rotates on the carbody/carrier through the slewing ring. The rubber components at this interface determine how vibration from the carrier engine and outrigger system transmits to the superstructure during lifting.
Slewing Ring Sealing and Vibration Isolation
The slewing ring (slew bearing) that allows superstructure rotation uses rubber lip seals to exclude contamination from the bearing raceway:
- Slewing ring outer lip seal: Protects the slewing bearing from rain, dust, and chemical contamination
- Inner seal: Retains the bearing lubricant
These seals are replaceable without removing the slewing ring and should be replaced at each major overhaul (typically every 5-10 years or 15,000 slewing hours depending on conditions).
Some crane designs incorporate rubber isolation pads between the slewing ring mounting flanges and the superstructure bed to reduce vibration transmission from road-driving powertrain to the superstructure. On Liebherr LTM cranes, these isolation pads are model-specific components that should not be substituted with generic mounting rubber.
Counterweight Mounting Rubber
Mobile crane counterweights attach to the superstructure through mechanical connections that use rubber cushion elements to:
- Absorb impact loads when counterweight sections are set down on the structure
- Prevent metal-on-metal contact that would accelerate wear at the attachment points
When counterweight cushion rubber degrades, the characteristic symptom is a metallic clang when counterweight sections engage their attachments — and visible wear marks on the steel contact faces.
Cab and Operator Station Isolation
Mobile crane operator cabs face an unusual vibration isolation challenge: the cab must isolate vibration during road travel (from the truck carrier powertrain) and during lifting operation (from the crane working load and slewing operations), with very different vibration spectra for each use case.
Liebherr LTM Cab Isolation System
Liebherr mounts the LTM cab on rubber isolation mounts at 4-6 positions. On the LTM 1100-5.2 and larger models, the cab can also luff (tilt backward) for visibility to the top of extended booms — the luff pivot uses rubber-cushioned bearings.
LTM cab mount specifications:
– Load per mount: 200-400 kg (heavy cabs with extensive electronics and LICCON system displays)
– Isolation frequency: 6-10 Hz
– Temperature range: Rated for full global deployment (-40°C to +55°C ambient)
The LICCON crane management computer generates precise load calculations during lifting. Cab vibration that exceeds certain thresholds can trigger LICCON vibration warning flags — a sign that cab isolation has degraded to a point where the system’s sensors are registering excessive motion.
Tadano ATF Cab Mounts
Tadano’s ATF (All-Terrain Fly jib) series uses a similar four-point cab mounting scheme. The ATF 220G-5 and ATF 400G-6 models have larger, heavier cabs due to the high-capacity crane management displays and are fitted with correspondingly heavier cab isolation mounts.
One notable feature: Tadano cab isolation mounts on AT models must accommodate cab movement during the carrier’s all-terrain suspension travel. The cab mounts see both static cab weight loading and dynamic inputs from the multi-axle hydropneumatic suspension. This dynamic loading is not present in RT cranes or truck-mounted cranes.
Engine and Powertrain Isolation
Large all-terrain cranes carry both a carrier powertrain (road driving) and sometimes a separate superstructure engine. Rubber isolation for these two powertrains differs in requirements.
Carrier Engine Mounts
AT crane carriers use heavy-duty truck engines: Mercedes-Benz OM473, Liebherr’s own D9508, or Scania DC16 variants. These are 400-600 kW engines mounted in an extremely compact carrier frame. Engine mount requirements:
- High load capacity (engine + transmission assembly: 1,800-2,500 kg)
- NR/SBR compound for oil and fuel resistance
- SAE J1171 type vibration isolation for commercial vehicle application
Engine mount condition directly affects driver comfort during the road transport phase, which can cover hundreds of kilometers between lift sites. For larger Liebherr and Grove cranes that travel internationally by road, mount condition is as important as for a long-haul truck.
Carrier Suspension Rubber Components
AT crane carriers use sophisticated multi-axle hydropneumatic suspension systems. The rubber components in these systems include:
- Axle pivot bushings: Allow each axle to articulate independently
- Hydraulic cylinder rod seals: Seal the suspension cylinders
- Anti-roll bar bushings: Connect the stabilizer bars to the carrier frame
Anti-roll bar bushing wear on a large AT crane is particularly consequential: worn bushings allow excessive chassis lean during cornering, which directly affects the crane’s lift configuration certification parameters.
For general guidance on shock absorber and suspension rubber, see our shock absorbers for construction equipment guide.
Winch and Hook Block Rubber Components
Hook Block Swivel Rubber Sealing
The hook block swivel — which allows the hook to rotate freely during lifts — uses rubber lip seals to retain the lubricant in the swivel bearing and exclude contamination. These seals:
- Must maintain flexibility at low operating temperatures (arctic deployments)
- Resist the hydraulic jack oil used in some hook assembly configurations
- Typically rated for 500-1,000 operational hours before replacement
Rope Drum Liner Pads
Some crane designs use rubber liner pads inside the wire rope drum grooves to protect the rope’s first layer. These pads:
– Reduce steel-on-steel rope crushing in the drum base layer
– Extend rope life at the first-wrapping contact point
– Compound: High-abrasion NR rated for rope compression loads
Grove GMK Series Rubber Parts
Manitowoc Grove GMK (Global Mobile Crane) all-terrain cranes are among the most widely deployed AT cranes globally. The GMK5250L, GMK6400, and GMK7550 all follow similar rubber parts architecture to Liebherr LTM cranes, with some notable differences:
- Grove uses a different outrigger beam guide bushing design — slide plates rather than cylindrical bushings, which affects the rubber compound specification
- GMK cab mounts are fewer (4-point) but larger diameter than equivalent Liebherr LTM mounts
- Carrier engine isolation on Grove GMK uses Volvo Trucks D16 or Mercedes OM473 — same engine families as highway trucks, so engine mount specifications are commercially available
For a comprehensive overview of crane rubber parts beyond mobile cranes, including crawler cranes and tower cranes, see our crane rubber parts and vibration isolation guide.
Quality and Certification for Safety-Critical Components
Mobile crane rubber parts operate in a safety-critical environment. When a rubber component fails on a crane in a lift configuration, the consequences may include dropped loads, crane tip-over, or structural damage. This places crane rubber parts in a higher criticality category than most construction equipment.
Quality requirements for mobile crane rubber:
– ISO 9001:2015 manufacturing quality management minimum
– Full dimensional traceability: Lot number and compound certificate for each component
– Hardness certification: Shore A tested per ASTM D2240 or ISO 7619-1 with results documented
– Compression set documentation: For seals and isolation mounts
Babacan Group manufactures mobile crane rubber components under ISO 9001:2015 quality management with full lot traceability. We supply to crane operators, lifting contractors, and Liebherr/Tadano/Grove authorized service centers. Browse our rubber mounts catalog or request a technical quote.
Shore Hardness Testing for Crane Rubber
For safety-critical applications, in-service Shore A hardness testing provides a documented condition record:
| Component | New Shore A | Replace Threshold |
|---|---|---|
| Cab isolation mounts | 40-50 | >65 or <30 |
| Outrigger beam buffers | 55-65 | >75 or visible cracking |
| Counterweight cushions | 60-70 | >80 or cracking at bond line |
| Engine mounts | 45-55 | >70 or bond separation |
Conclusion
Mobile crane rubber parts carry safety responsibilities that extend well beyond typical construction equipment. Outrigger system integrity affects ground bearing calculation accuracy. Slewing ring seals protect bearings rated for tens of thousands of tonne-meters of moment. Cab isolation determines whether the operator sees and thinks clearly during complex lifts.
Key takeaways for crane operators and maintenance managers:
– Outrigger beam buffers are low-cost components with high operational safety relevance — inspect at every annual
– AT crane cab mounts must accommodate both road driving and lifting operation vibration spectra
– Slewing ring lip seals protect one of the most expensive single components on the crane — replace on schedule
– For safety-critical applications, require Shore A documentation with all rubber components
Babacan Group supplies mobile crane rubber parts with full traceability to lifting contractors and crane rental companies in 84+ countries. Request a technical quote for your Liebherr, Tadano, or Grove model.