MOT Test of Suspension | Axles | What is checked

MOT Test of suspension

Axles and Suspension (5)

(Formerly MOT Test of suspension)

The grouping of MOT checks has changed with the May 2018 revised Testing Manual, and suspension is now included in the ‘Axles, Wheels, Tyres and Suspension’ section.

To simplify the descriptions we are including Test descriptions of checks for axles with the suspension checks here, and wheels and tyres are now grouped together in the new ‘Wheels and Tyres’ section.

All vehicle suspension systems consist of mechanical components and joints connecting the wheels to the vehicles structure via a spring system of one form or another (which isn’t necessarily a mechanical spring) which enables the wheels to move up and down according to the terrain – the bumps and depressions in the road. Due to the recent proliferation of pot-holes in roads, suspension failures have become more frequent, especially failures of steel springs.

Some suspension systems will be more complex than others and many of the checks cannot be done without elevating the vehicle on a specialised vehicle lift so the Tester can inspect the appropriate parts of the vehicle’s suspension from underneath.

All the mechanical joints, levers, springs and other items associated with the suspension system will be inspected (for breaks, cracks, excessive corrosion and so on), together with the condition of the vehicle’s structure to which the suspension system is attached.

Axles

Testers may use mechanical wheel play detectors when checking axle security on beam axles.
View a short clip of play detectors being used here

The following categories apply to defects in this section:

DefectCategory
a. An axle fractured
Dangerous
b. An axle:
i. insecure or with loose fixing bolts
Major
ii. insecure such that stability is impaired or functionality affected
Dangerous
c. An axle:
i. with an unsafe modification
Major
ii. modified so that vehicle stability is impaired or axle functionality affected
Dangerous

Suspension

Under bonnet checks:

  • upper suspension joints
  • any other suspension components which can be inspected from beneath the bonnet

Under vehicle checks:

Applies to the front and rear suspension

  • no split pins or nuts missing, no components broken or excessively damaged
  • road springs are checked for condition
  • all suspension joints are checked for condition
  • shock absorbers (dampers) must not leak and must be secure (the vehicle will be ‘bounced’ by the Tester to check that they damp the springs adequately).

The suspension is checked for wear by the assistant applying loads in various ways with the wheels jacked up whilst the Tester observes the result from beneath the vehicle. This may include the use of approved wheel play detectors in some Test Stations.

Note: There are numerous different suspension systems, and the specific nature of any examination will depend to a large extent on the design of the suspension system.

The following categories apply to defects in this section:

DefectCategory
a. A spring:
i. insecurely attached to chassis or axle
Major
ii. with fixings loose to the extent that relative movement is visible
Dangerous
b. A spring:
i. or spring component fractured or seriously weakened
Major
ii. main leaf fractured
Dangerous
c. A spring:
i. missing
Major
ii. missing and directional control affected
Dangerous
c. A spring:
i. with an unsafe modification
Major
ii. modified so that the suspension is inoperative
Dangerous

Shock absorbers

Missing shock absorbers will be rejected only if they were fitted as standard.

The following categories apply to defects in this section:

DefectCategory
a. A shock absorber:
i. insecurely attached to chassis or axle
Major
ii. defective
Dangerous
ii. missing or likely to become detached
Major

Suspension arms, rods, struts, sub-frames, anti-roll bars etc.

The Tester will check suspension components for corrosion.

The following categories apply to defects in this section:

DefectCategory
a. A suspension component:
i. insecurely attached to chassis or axle
Major
ii. missing, likely to become detached or directional stability impaired
Dangerous
b. A suspension component:
i. excessively damaged or corroded
Major
ii. fractured or likely to failDangerous
c. A suspension component:
i. with an unsafe modification
Major
ii. modified so that the suspension is inoperative or likely to fail other components
Dangerous

Suspension arms, rods, struts, sub-frames, anti-roll bars etc.

Some vehicles use thin gauge steel pressings for some highly stressed suspension components. Many of these parts have hollow ‘box sections’ or up-facing areas that can collect road dirt, salt or other chemicals that can cause severe local corrosion.

These areas will be closely inspected by the Tester.

Suspension joints, pins and bushes (5.3.4)

Some rubber/synthetic bushes in suspension joints are designed to allow some movement.

The Tester will only reject rubber or synthetic bushes which show serious deterioration of the bonding or flexible material.

MacPherson strut top bushes are designed to have significant lateral play when the suspension is hanging free. The Tester will only reject MacPherson strut top bushes when play is due to wear or maladjustment.

The Tester will assess wear or play in spring pins and bushes using various methods, including with play detectors.

The following categories apply to defects in this section:

DefectCategory
a. A suspension pin, bush or joint:
i. excessively worn
Major
ii. likely to become detachedDangerous
b. A suspension joint dust cover:
i. severely deteriorated
Minor
ii. missing or no longer prevents the ingress of dirt etc.Major

Gas, air and fluid suspension

The following categories apply to defects in this section:

DefectCategory
a. A gas, air or fluid suspension system inoperative
Dangerous
b. A gas, air or fluid suspension system component damaged, modified or deteriorated in a way that:
i. it would adversely affect the functioning of the system
Major
ii. its function is seriously affected
Dangerous
c. An obvious leak from any part of the system
Major

Complete suspension system

The strength and continuity of the vehicle’s load bearing members and their supporting structure or panelling around any spring, sub-frame or suspension component mounting will be checked.

The following categories apply to defects in this section:

DefectCategory
a. The strength or continuity of the load bearing structure within 30cm of any sub-frame, spring or suspension component mounting (a ‘prescribed area’):
i. is significantly reduced or inadequately repaired
Major
ii. is so weakened that control of the vehicle is likely to be adversely affected
Dangerous

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