Chapter 3 — Section 2: Steering and suspension

The steering and suspension systems represent the mechanical interface between the driver’s inputs and the road surface. In the context of the MOT test, Section 2 is dedicated to ensuring that this interface remains precise, predictable, and structurally sound. The inspection is largely divided into two methodologies: visual assessment for degradation—such as fluid leaks or perishing rubber—and physical testing for excessive movement or 'play' within mechanical joints. A failure in these components rarely occurs in isolation; a worn bush often leads to accelerated tyre wear or compromised braking stability, making this section one of the most common sources of 'Major' and 'Dangerous' defect classifications.

01Steering Linkage and Ball Joints

The primary focus of the steering linkage inspection is the integrity of the track-rod ends and the steering rack itself. Testers are required to check for 'excessive play' in the ball joints, which is typically assessed by rocking the road wheels while the vehicle is over a pit or on a lift. The DVSA MOT Inspection Manual does not provide a specific millimetre threshold for play, as the tolerance varies by manufacturer, but any movement that suggests the ball and socket are no longer seated securely will usually result in a failure.

• Inspection of the dust covers (boots) is a critical sub-check; a split or missing boot that allows dirt ingress is a Major defect.
• Steering rack gaiters must be secure and free from significant tearing that could allow the escape of lubricant.
• Movement of the steering rack body relative to the chassis, often caused by perished mounting bushes, is a common failure point on older vehicles.
• Power steering systems are inspected for fluid leaks, with 'seepage' often noted as an advisory, while a continuous drip is a failure.

02Suspension Springs and Mounting Units

Suspension springs, whether coil, leaf, or torsion bar, are subject to immense vertical loads and constant exposure to road salt and moisture. The most frequent failure in this category is a fractured coil spring. Testers look for breaks, usually occurring at the very top or bottom of the coil where moisture traps against the spring seat. If a spring is found to be cracked or broken, it is a Major defect. If the break is such that the spring could become displaced from its mounting, it is classified as Dangerous.

• Leaf springs are checked for cracks in individual leaves and the security of 'U' bolts.
• Air suspension systems are tested for leaks and the ability of the compressor to maintain ride height.
• Bonded suspension bushes—the rubber-to-metal joints—are inspected for 'delamination', where the rubber has physically separated from the metal sleeve.

03Shock Absorbers and Damping Efficiency

The MOT test for shock absorbers (or dampers) is primarily a visual and manual check rather than a laboratory-grade performance test. Testers look for evidence of fluid leakage; a light misting is acceptable (Advisory), but a visible leak that has reached the lower mounting point is a failure. The unit must also be securely attached to the vehicle. A simple 'bounce test' is often performed by depressing the corner of the vehicle; if the car continues to oscillate more than once or twice, the damper is deemed ineffective.

04Control Arms, Panhard Rods, and Anti-roll Bars走向

The structural members of the suspension, including wishbones and trailing arms, must be free from significant corrosion that weakens the component. The 'hammer test' may be used by the tester to determine if the metal has thinned to the point of compromising structural integrity. Anti-roll bar links (often referred to as 'droplinks') are a high-volume failure item. While they rarely pose an immediate safety risk compared to a ball joint, a snapped droplink or a perished bush in the link will result in a Major defect.

• Anti-roll bar bushes are checked for excessive clearance.
• Panhard rods and torque arms are inspected for security and the condition of their end-fixings.
• Any repair to these components using welding is generally prohibited unless specifically permitted by the manufacturer, as it can alter the heat treatment of the metal.

05Wheel Bearings and Hub Assembly走向

While wheel bearings are technically part of the transmission of movement, they are inspected under Section 2 because they are integral to the corner assembly. The tester will spin the wheel to listen for the distinctive rumbling or rough running that indicates a failing bearing. Physical play is also checked. A small amount of play is often permissible in older vehicles with adjustable taper-roller bearings, but modern sealed units should typically have no perceptible movement. Any roughness or excessive play that affects the steering or braking performance will result in a failure.

06Defect Thresholds and Severity Classification

The transition from an 'Advisory' to a 'Major' defect often depends on the tester’s professional judgment regarding the 'clearance' in a joint. If a ball joint has movement but remains within what the tester deems a safe operating window for the vehicle's age, it will pass with an advisory. However, if the joint shows 'excessive' wear—meaning there is a risk of the joint popping out or the steering becoming imprecise—it must fail. 'Dangerous' defects are reserved for components that are likely to fail imminently or have already failed in a way that prevents the driver from controlling the vehicle, such as a completely detached steering rack or a snapped steering column universal joint.

Section 2 remains a rigorous part of the MOT, focusing on the mechanical junctions that keep a vehicle stable. While much of the criteria is subjective, the focus is always on preventing the catastrophic failure of steering or suspension components while in motion.