In the heavy transport sector, profitability is measured not only by the kilometres travelled, but also by the time the vehicle spends out of the workshop. For a fleet, a lorry stopped by an unexpected breakdown represents a direct loss of income, emergency logistics costs and, in the worst case, road safety risks, which is why preventive maintenance is vital.
At Industrias Onyarbi, we understand that the quality of replacement parts is essential, but their optimal performance depends on a rigorous preventive maintenance strategy. Below, we present a comprehensive technical guide to ensuring the longevity of the most critical components of the unit and semi-trailer.
The Running Gear: The Heart of Stability
Wear on axle and suspension components is usually gradual and silent. A failure here affects not only the tyre, but the entire chassis structure.
Suspension Systems: In pneumatic suspensions, check the condition of the air springs (diapreses). Look for cracks, porosity, or friction with the chassis. In leaf springs, ensure that there are no broken leaves and that the silent blocks do not have excessive play.
Axle Alignment: A misaligned axle on a semi-trailer increases fuel consumption by up to 3% and causes premature tread degradation.
Braking System: Safety Without Compromise
The braking system is possibly the area where preventive maintenance is most critical. In heavy-duty configurations, heat is the main enemy.
Disc Brakes vs. Drum Brakes
Discs and Pads: Check the thickness of the brake pad. If the friction material is below the manufacturer’s limit, the risk of crystallisation and damage to the disc increases. Look for radial cracks in the brake disc that exceed safety tolerances.
Drums and Linings: Check the condition of the brake cams and automatic adjusters (levers). A seized adjuster will cause uneven braking, affecting the stability of the assembly.
Pneumatic Circuit: Drain the air reservoirs weekly to remove condensation. The presence of water or oil in the system can degrade the control valves and actuators (brake chambers).
Connecting and Articulation Elements
The connection between the tractor unit and the semi-trailer is the point of maximum mechanical stress.
Fifth Wheel: Clean off old grease to inspect the plate for possible cracks. Check the tightness of the lock on the king pin to prevent jolts and structural damage during acceleration and braking.
King Pin or Hitch Pin: Use a gauge to measure the wear on the pin diameter. Wear exceeding 2 mm requires immediate replacement of the component to prevent accidental disengagement.
Support legs: Lubricate the internal gears of the semi-trailer’s support legs. A dry mechanism can jam under load, making unhitching operations difficult.
Electrical and Lighting System
With the implementation of active safety systems such as EBS and ABS, the integrity of electrical wiring is vital.
Connectors and Hoses (Coils): Check that the air hoses and electrical cables do not show any cuts or burns caused by friction. The 7- and 15-pin connectors must be free of corrosion (sulphation) to ensure data transmission to the semi-trailer modulator.
Optical Systems: Replacing burnt-out lamps is essential, but preventive maintenance involves checking the watertightness of the pilot lights to prevent short circuits caused by moisture ingress.
Quick Verification Checklist (Reference Table)
| Component | Frequency | Main Action |
| Fluid Levels | Daily | Check oil, coolant and AdBlue. |
| Tyre Pressure | Weekly | Adjust according to load to prevent deformation. |
| Chassis Lubrication | Monthly | Lubricate friction points and fifth wheel. |
| Braking Valves | Quarterly | Check for air leaks and valve response. |
| Tightening Nuts | Quarterly | Check the tightening torque on the wheel studs. |
The Importance of Quality in Replacement Parts
Performing preventive maintenance with low-quality components is often counterproductive. A bearing that does not meet heat treatment tolerances or a brake pad with an unstable friction coefficient can compromise all the previous inspection work.
At Industrias Onyarbi, we manufacture and select spare parts that exceed original equipment (OE) standards. We understand that every part counts when it comes to keeping the logistics chain moving. Using certified spare parts not only guarantees that the part will fit, but also that the preventive maintenance cycle can be extended with complete confidence.
Conclusion
Preventive maintenance is not an expense, it is an investment in operational availability. A lorry that follows a strict servicing programme reduces its total operating costs (TCO) and maintains a higher resale value. By combining meticulous technical inspection with high-quality spare parts, we ensure that road transport is safer, more efficient and more profitable.
Would you like to optimise your fleet’s spare parts stock? At Industrias Onyarbi, we have a catalogue specialising in axles, brakes and suspension. Contact our technicians for personalised advice.
