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.
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.
Read our guidelines about using safety chains on heavy trailers [PDF, 270 KB] – Nov 2016
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.
Read our information sheet and about skid plate guide(external link)
Go to the Vehicle inspection portal to download the Operator statement of skid plate inspection and maintenance forms for 50mm and 90mm:
NZTA 4085B operator statement of skid plate inspection and maintenance(external link)
These forms are used by a heavy vehicle operator to confirm a vehicle’s skid plate structural condition is within safe tolerances.
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.
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.
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 should:
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.
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
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.
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.
Read our information sheet about wheel security – Sep 2010
Maintenance workshops and mechanics should:
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.
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.
Cardan shaft park brakes aren’t currently tested in roller brake machines because it is thought that the differential, driveline and/or park brake mechanism may be damaged in testing.
We commissioned independent testing of cardan shaft park brakes on trucks with a simulated slope (pull) test and in a brake roller machine and found no damage to the trucks’ driveline and park brake assemblies.
Read the report about testing cardan shaft park brakes in roller brake machines [PDF, 1.4 MB] – June 2021
A procedure for testing cardan shaft park brakes in roller brake machines will be developed in the future to test a range of vehicle types to give greater confidence that roller brake machines can be used to test cardan shaft park brakes and allow the test procedure to be refined.