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Title / Describe heavy trailer systems, and maintain and repair heavy trailers and semi-trailers
Level / 4 / Credits / 15
Purpose / This unit standard is for people in the automotive heavy repair industry. People credited with this unit standard are able to: demonstrate knowledge of drawbar trailer and semi-trailer configuration and suspension; demonstrate knowledge of trailer and semi-trailer air braking systems; demonstrate knowledge of trailer steering and semi-trailer self-steering systems; determine the need for service and repair of drawbar trailer and semi-trailer air braking systems; rectify drawbar trailer and semi-trailer air braking system faults; service and repair trailer and semi-trailer suspension faults; and check and adjust semi-trailer wheel alignment.
Classification / Motor Industry > Automotive Trailers
Available grade / Achieved
Explanatory notes
1 All trailer repairs and alterations must conform to the requirements of the Transport (Vehicle Standards) Regulations 1990 and amendments.
2 All welding to towbars, drawbeams and drawbars must conform to NZS 5446 1987 and be performed by a person holding a current NZS 4711 Welding Certificate.
3 Brake equipment, repairs and alterations to equipment and replacement parts must conform to the requirements of the New Zealand Heavy Vehicle Brake Code.
4 The following legislation and amendments are required to be consulted and followed where applicable:
– Health and Safety in Employment Act, 1992.
5 Reference to suitable tools and equipment means industry approved tools and equipment that are recognised within the industry as being the most suited to complete the task to a professional and competent manner with due regard to safe working practices.
6 Because of the particular nature of this unit standard, it is essential that the practical assessment evidence is obtained from commercial jobs in the workplace under normal workplace conditions.
Outcomes and evidence requirements
Outcome 1
Demonstrate knowledge of drawbar trailer and semi-trailer configuration and suspension.
Evidence requirements
1.1 Tractor, semi-trailer and trailer configurations are described according to manufacturer’s specifications.
Range A Train, B Train.
1.2 Drawbar trailer axle systems are described according to manufacturer’s specifications.
Range two axle, three axle, four axle.
1.3 Semi-trailer axle systems are described according to manufacturer’s specifications.
Range single axle, two axle, three axle.
1.4 Drawbar trailer and semi-trailer suspension systems are described according to manufacturer’s specifications.
Range single axle, close and wide-space tandem, close and wide-space tri-axle.
Outcome 2
Demonstrate knowledge of trailer and semi-trailer air braking systems.
Evidence requirements
2.1 The operation of the trailer and semi-trailer air braking systems are described according to manufacturer’s specifications.
Range air lines, air supply and storage, automatic drain valve, brake chamber, slack adjuster, spring brake, relay-breakaway valve, tractor protection valve, air operated trailer coupling, air operated levelling system.
Outcome 3
Demonstrate knowledge of trailer steering and semi-trailer self-steering systems.
Evidence requirements
3.1 Drawbar trailer towing and turning systems are described according to manufacturer’s specifications.
Range friction turntables, drawbars.
3.2 Semi-trailer turntables are described according to manufacturer’s specifications.
Range friction type, anti-friction type;
semi-oscillating, compensating.
3.3 Semi-trailer kingpins and locking devices are described according to manufacturer’s specifications.
3.4 Semi-trailer turntable self-steering is described according to manufacturer’s specifications.
3.5 Semi-trailer castering axle self-steering is described according to manufacturer’s specifications.
Range forward steering, steering control and damping, reverse locking.
Outcome 4
Determine the need for service and repair of drawbar trailer and semi-trailer air braking systems.
Evidence requirements
4.1 Safe working practices are observed throughout the task.
Range personal safety, safety of others, equipment safety.
4.2 The operation of the trailer-semi-trailer air braking system is checked according to manufacturer’s workshop manual instructions, and any faults found are noted.
4.3 The brake shoes, springs, backplates, operating mechanisms, brake drums, slack adjusters and brake chambers are inspected, and any faults found are noted.
Range wear, scoring, runout, distortion, condition of friction linings, spring brake operation.
4.4 The air brake components are inspected in-situ and any signs of air leaks and damage are noted.
Range condition of pipes and hoses, joints, cylinders and valves.
4.5 Drawbar steering and turntable self-steering system maintenance schedules are checked and the steering systems are inspected for wear and damage and the results noted.
Range drawbar coupling, turntables, friction plates, steering links, turntable kingpins, locking device.
4.6 Castering axle self-steering is checked for wear and damage and any faults found are noted.
Range king pins, tie rod, damping control, reverse lock, wheel alignment.
Outcome 5
Rectify drawbar trailer and semi-trailer air braking system faults.
Evidence requirements
5.1 Safe working practices are observed throughout the task.
Range personal safety, safety of others, equipment safety.
5.2 Suitable tools and equipment are selected and used that enable the rectification work to be carried out.
5.3 Faults noted in the air operated brake equipment are rectified to meet the manufacturer's requirements and the New Zealand Heavy Vehicle Brake Code.
Range spring brake, tractor protection valve, relay-breakaway valve, automatic drain valve, air hoses and lines.
5.4 The wheel stations are disassembled, repaired, and reassembled in the manner and sequence prescribed by the manufacturer to restore full serviceability and to meet the manufacturer's specifications.
5.5 The brake shoes and slack adjusters are adjusted to meet the manufacturer's requirements.
5.6 The braking system is tested to ensure no faults remain.
Outcome 6
Service and repair trailer and semi-trailer suspension faults.
Evidence requirements
6.1 Safe working practices are observed throughout the task.
Range personal safety, safety of others, equipment safety.
6.2 The trailer and semi-trailer suspensions are checked for misalignment, wear and damage, and any faults are noted.
Range leaf springs, air springs.
6.3 Any misalignment, wear and damage to the suspension system is repaired by replacement with manufacturer's approved replacement parts.
Range spring leaves, shackles, hangers, equaliser bars, torque rods, air bellows, levelling valve and associated equipment, shock absorbers.
Outcome 7
Check and adjust semi-trailer wheel alignment.
Evidence requirements
7.1 Safe working practices are observed throughout the task.
Range personal safety, safety of others, equipment safety.
7.2 Suitable tools and equipment are selected and used that enable the semi-trailer wheel alignment to be checked.
7.3 Semi-trailer wheel alignment is checked following the method prescribed by the alignment equipment manufacturer, and any misalignment is noted.
7.4 Adjustments are made to the wheel alignment to return it to full serviceability as prescribed by the trailer manufacturer.
Replacement information / This unit standard has been replaced by unit standard 23931 and unit standard 23932.This unit standard is expiring. Assessment against the standard must take place by the last date for assessment set out below.
Status information and last date for assessment for superseded versions
Process / Version / Date / Last Date for Assessment /Registration / 1 / 28 September 1994 / 31 December 2016
Review / 2 / 21 February 1999 / 31 December 2016
Review / 3 / 21 September 2007 / 31 December 2016
Rollover / 4 / 19 November 2010 / 31 December 2016
Rollover / 5 / 18 February 2016 / 31 December 2020
Consent and Moderation Requirements (CMR) reference / 0014
This CMR can be accessed at http://www.nzqa.govt.nz/framework/search/index.do.
Please note
Providers must be granted consent to assess against standards (accredited) by NZQA, or an inter-institutional body with delegated authority for quality assurance, before they can report credits from assessment against unit standards or deliver courses of study leading to that assessment.
Industry Training Organisations must be granted consent to assess against standards by NZQA before they can register credits from assessment against unit standards.
Providers and Industry Training Organisations, which have been granted consent and which are assessing against unit standards must engage with the moderation system that applies to those standards.
Consent requirements and an outline of the moderation system that applies to this standard are outlined in the Conesnt and Moderation Requirements (CMR). The CMR also includes useful information about special requirements for organisations wishing to develop education and training programmes, such as minimum qualifications for tutors and assessors, and special resource requirements.
NZ Motor Industry Training Organisation (Incorporated)SSB Code 101542 / Ó New Zealand Qualifications Authority 2016