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Regular vehicle maintenance is sound business practice that ensures vehicles use fuel efficiently and prevents avoidable and costly breakdowns.

This section outlines current issues which are beyond routine maintenance requirements. All those with an interest in the safe operation of heavy vehicles need to be aware of these issues.

Using safety chains on heavy trailers

Some operators have begun fitting safety chains between their heavy trucks and trailers to provide an additional safety backup between the primary coupling and the breakaway brake function. Safety chains allow a driver to bring a trailer to a controlled stop in the event of primary coupling failure, provided guidelines are met.

The Transport Agency reiterates that it is still comfortable with the current practice of using a primary coupling and breakaway brake.

However, for operators who want an additional level of safety, the installation of safety chains is a safe and legal option. The following guidelines must be followed otherwise there is risk of not being able to bring a trailer to a controlled stop.

Guidelines

Read our guidelines about using safety chains on heavy trailers [PDF, 270 KB] – Nov 2016

Skid plate inspections

King pins and skid plates need appropriate inspection and maintenance. This is especially important where the design of the skid plate makes it difficult or even impossible for inspection to be carried out.

In these circumstances the potential for corrosion and eventual structural failure and resultant detachment from the towing vehicle is a significant risk.

Operators, drivers and mechanics, as well as trailer designers, certifiers and vehicle inspectors, all need to take appropriate action to ensure trailer detachment does not occur.

Information sheet

Read our information sheet and about skid plate guide(external link)

Form

Go to the Vehicle inspection portal to download the 50mm and the 90mm NZTA 4085B operator statement of skid plate inspection and maintenance forms(external link).

These forms are used by a heavy vehicle operator to confirm a vehicle’s skid plate structural condition is within safe tolerances.

Driveshafts

Heavy vehicle driveshafts and their components, especially the universal joints, need appropriate maintenance, otherwise their life will be shortened dramatically, and they may fail prematurely. Operators, drivers and mechanics, as well as engineers, certifiers and vehicle inspectors, all need to take appropriate action to avoid these potentially dangerous failures.

Drivers

Drivers should:

  • engage and disengage the clutch smoothly and gradually, especially when starting or changing gear under heavy load, eg when driving uphill

  • avoid abrupt use of the clutch, as this places higher loads on the driveline, which may cause damage to the driveshaft, or in extreme cases, may lead to immediate driveshaft failure

  • be alert to any unusual vibration (eg on the gearshifting lever) that may indicate a problem with the driveshaft. Other signs include knocking sounds when starting the vehicle, and/or during gear changes. If vibration or knocking increases, the driveshaft may be about to fail – you must immediately slow down, stop the vehicle, and check the driveshaft.

If driveshaft failure occurs at high vehicle speed, the risk of harming other road users increases significantly.

Transport operators

Operators should ensure:

  • that driveshafts are maintained and checked regularly

  • that this maintenance work is carried out according to the manufacturer's written instructions. Industry experience has indicated that, in some cases, you need to lubricate and check driveshafts more frequently than specified by the manufacturer.

Maintenance workshops and mechanics

Maintenance workshops and mechanics should:

  • check and maintain the driveshaft according to the manufacturer's instructions. The instructions are likely to include the following directions:
    •  'purge-lubricate' with specified lubricant: greasing must be continued until the fresh lubricant is discharged from all outlets of the lubricated component
    • ensure that the pressure is not too high as excessive pressure can damage or blow out the seals of universal joints, which in turn will lead to reduced component life
  • check the condition (damage, wear, deterioration, excessive play) of all components
  • check that all bolts and nuts are present and properly tightened
  • check that the bearing cups of the universal joints are correctly positioned, secure, and not able to rotate.

By repairers

Workshops and mechanics that repair driveshafts or carry out repairs where the driveshaft is partially or fully removed from the vehicle must follow the manufacturer's repair instructions. Instructions are likely to include the following directions:

  • Thoroughly clean components that are allowed to be re-used. Inspect (replacing if necessary) and lubricate these before re-assembly. Components that are required to be replaced once disassembled must be replaced even if they appear to be in good condition. These components may include bolts, nuts, locking tabs, the straps of universal joints, etc.

  • Phase the universal joints as prescribed by the manufacturer.

  • Properly tighten all bolts and nuts.

  • Use locking devices as specified by the manufacturer.

Certifiers

Heavy vehicle specialist certifiers should ensure that the requirements, which are in force in respect of driveshaft modifications, are complied with. 

Read more about modifying a heavy vehicle

By vehicle inspectors

Certificate of fitness (CoF) inspections include detailed inspection requirements for driveshafts. CoF inspectors should check the condition of driveshafts and their components according to the updated requirements.

Wheel security

Wheels on heavy vehicles need to be properly fitted and maintained otherwise there is a high risk of wheel loss or wheel insecurity – which could lead to a serious crash.

A wheel is subject to a number of forces which act to loosen the wheel nuts.

If one of the wheel nuts loosens then these forces are distributed over the remaining nuts, which can cause the adjacent nuts to loosen as well. As more nuts become loose the process accelerates as the overall clamping force holding the wheel in place decreases.

When the clamping force reduces sufficiently the wheel will move on the hub. This results in side loading and further loosens the remaining nuts, which, if not spotted in time, leads to elongated stud holes, fatigue failure of studs, fretting cracks and in many cases wheel loss.

Loose wheel nuts can occur due to a number of reasons, including: under-torquing, over-torquing, incompatible parts, poor mating surface condition and through not following the manufacturer’s instructions.

Information sheet

Read our information sheet about wheel security – Sep 2010

Equipment

  • Equipment used to fit wheels needs to be appropriate for the task and in a serviceable condition.
  • Torque wrenches should be maintained and calibrated on a regular basis.

Transport operators

Operators should:

  • ensure drivers inspect tyres and wheels during pre-trip walk around inspections
  • ensure that after a wheel has been fitted the wheel nuts are rechecked for correct torque after a short period of in-service running
  • ensure that wheel nuts are checked for security and tightened
  • establish causes of wear and damage on loose nuts before re-tightening
  • ensure that manufacturer’s written instructions are followed by correctly trained persons and that comprehensive maintenance records are kept
  • consider fitting loose wheel nut indicators.

Maintenance workshops and mechanics

Maintenance workshops and mechanics should:

  • establish causes of wear and damage on loose nuts before retightening
  • ensure removal and fitting of wheels are carried out to manufacturer’s instructions
  • ensure all hub/drum and wheel mating surfaces are clean and allow a flush fit with the mounting surfaces of the wheel
  • use the correct tightening sequence (wheel nut tightening procedures can vary for different types of wheels with different types of wheel nuts)
  • ensure nuts run freely over the whole length of the stud thread by hand
  • use a calibrated torque wrench for the final tightening
  • ensure that the wheel nuts are re-torqued after a short period of in-service running (between 50 to 100 kms is commonly recommended)
  • simply retighten nuts to the recommended torque when re-torquing (do not slacken and re-tighten)
  • ensure that manufacturer’s written instructions are followed by correctly trained persons and that comprehensive maintenance records are kept.

Certifiers

Heavy vehicle specialist certifiers should ensure that the requirements, which are in force in respect of wheel modifications, are complied with and that the operator has the relevant technical information.

Vehicle inspectors

Certificate of fitness (CoF) inspections include inspection requirements for wheels and wheel nuts. CoF inspectors should check the condition and security of wheels and wheel nuts and their associated components according to the requirements.

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