Understanding Secondary Brake Performance

The Importance of Secondary Brake Performance

When we think about vehicle safety, the braking system is paramount. While the primary service brake is the first line of defence, understanding and ensuring the performance and efficiency of the secondary brake system is equally critical. This system acts as a backup in case of primary brake failure, providing a vital layer of safety for drivers, passengers, and other road users. This article delves into the intricacies of secondary brake performance, its regulatory context, testing methodologies, and common issues encountered during vehicle inspections.

Regulatory Framework for Braking Systems

The legal requirements for braking systems in the UK are primarily governed by the Road Vehicles (Construction and Use) Regulations 1986. Specifically, regulations 15, 16, 18(1), 19, and 87 lay out the fitting, maintenance, and efficiency standards. For vehicles first used on or after 1st April 1983, EC braking requirements (Regulation 15) are generally applicable, while Construction and Use requirements (Regulation 16) apply to older vehicles, with specific exemptions.

When to Calculate Brakes Based on Design Weights

For most goods vehicles first used on or after 1st April 1983, braking systems are subject to type approval and must meet stringent EEC Directive 79/489 standards. The braking force is expressed as a percentage of the gross vehicle weight (GVW). However, when a vehicle's design weights exceed the maximum authorised GVW for the UK, the brakes must be calculated using the design weight. This ensures that even at higher potential loads, the braking system remains effective.

Minimum braking efficiency requirements for type-approved vehicles first used on or after 1st April 1983, and non-type-approved goods vehicles registered between 1st January 1986 and 1st April 1983, are as follows:

Anti-lock Braking Systems (ABS)

ABS is a crucial safety feature, particularly for heavier vehicles. Goods vehicles exceeding 16,000kg GVW (or authorised to tow trailers exceeding 10t GVW) first used from 1 April 1992, and trailers exceeding 10t GVW manufactured from 1 October 1991, must be fitted with ABS. Furthermore, from 1 May 2002, goods vehicles and trailers exceeding 3500kg must have ABS, with specific exemptions for certain public works vehicles.

Service Brake Performance and Efficiency

The primary brake tester must be used unless the vehicle's drive configuration, transmission type, or braking system makes it unsuitable. In such cases, a decelerometer test may be appropriate. For roller brake testers (RBTs), if more than half of the wheels of a brake system lock, the efficiency requirements for that system are considered met. For L7 vehicles with a single service brake control operating all wheels, the efficiency requirement is 50%.

Secondary Brake Performance and Efficiency

The secondary brake system, often referred to as the 'emergency brake' or 'parking brake', is designed to bring the vehicle to a stop if the primary system fails. Its performance and efficiency are rigorously tested. Similar to the service brake, if more than half of the wheels of a brake system lock during an RBT test, the efficiency requirements are deemed satisfied.

Testing the Secondary Brake

The method for testing the secondary brake's performance and efficiency can vary. The primary brake tester is the preferred method. However, if the vehicle is unsuitable for this, a decelerometer or a gradient test may be used. A gradient test is typically reserved for situations where the parking brake cannot be tested using other methods, often on all-wheel-drive vehicles with electronic parking brakes where technical information is limited.

Parking Brake Performance and Efficiency

The parking brake's function is to hold the vehicle stationary, especially on gradients. Its performance is assessed using the primary brake tester, or if unsuitable, a decelerometer or gradient test. The gradient test is a last resort, usually for specific all-wheel-drive vehicles with electronic parking brakes where manufacturer data is unavailable.

Efficiency Calculation for Parking Brakes

When using an RBT, if over half of the wheels of the parking brake system lock, the efficiency requirements are met. This ensures a consistent standard across different testing scenarios.

Common Brake Defects and Inspection Points

During vehicle inspections, several areas related to the braking system are scrutinised:

• Rigid Brake Pipes: Repairs to pressure lines using unsuitable connectors, such as compression joints with separate ferrules, are unacceptable and will result in a failure. Unacceptable repairs should be failed using RfR 1.1.21 (d).
• Brake Shoes on Hub Assembly: While brake drums and discs are part of the wheel, their condition and fitment are crucial for the braking system's overall efficiency.
• Anti-lock Braking System (ABS): While not all vehicles manufactured after 1 January 2010 have ABS, its obvious removal on vehicles where it should be present will lead to a failure.
• Electronic Power Steering (EPS): Any steering system incorporating an electric motor for control or assistance falls under this category for inspection purposes.
• Tyres: While spare tyres are not part of the mandatory inspection, any visible defects on them should be advised to the presenter. For vehicles with more than 8 passenger seats, tyre age and date codes are inspected from 1 February 2021. Asymmetric tyres fitted incorrectly are not a reason for rejection but should be advised.
• Shock Absorbers: A shock absorber exhibiting negligible damping effect will be rejected, with a specific defect code (d) for major failure.
• Suspension Joints, Pins and Bushes: Play in these components, checked by rocking and shaking the wheels, is a critical inspection point.
• Gas, Air and Fluid Suspension: Technicians must be aware of the health and safety hazards when testing vehicles with these suspension types, referring to the introduction's health and safety section for guidance.
• Fuel System Heat Shields: Vehicles should only be failed for missing heat shields if there is a demonstrable fire risk with other fuel system components.
• Towbar Mounting Points: The vehicle structure within 30cm of any towbar mounting point must be inspected for strength and continuity. Rejection is only warranted if the strength or continuity is significantly reduced.

Health and Safety Considerations

When inspecting vehicles, particularly those with gas, air, or fluid suspension, technicians must be mindful of potential health and safety hazards. Additionally, when inspecting electrical wiring, awareness of high-voltage components and cabling is crucial, as they can pose a risk of fatal electric shock.

Recording Defects

Best practice dictates thorough and accurate recording of all identified defects. This ensures clear communication with the vehicle presenter and maintains a proper record for compliance and future reference.

Frequently Asked Questions

Q1: What is the secondary brake system?
A1: The secondary brake system is a backup braking system designed to stop the vehicle if the primary service brake fails.

Q2: When are brakes calculated based on design weights?
A2: Brakes are calculated using design weights when a vehicle's design weights exceed its maximum authorised gross vehicle weights for the UK.

Q3: What is the minimum efficiency for a secondary braking system?
A3: The minimum efficiency requirement for a secondary braking system is 25% for type-approved vehicles and certain goods vehicles.

Q4: Is it acceptable to repair rigid brake pipes with compression joints?
A4: No, repairs to pressure lines using compression joints with separate ferrules are unacceptable and will result in a failure.

Q5: What happens if more than half of the wheels lock on a roller brake tester?
A5: If more than half of the wheels of a brake system lock on an RBT, the efficiency requirements for that system are considered to be met.

Q6: Are there any special considerations for testing ABS?
A6: Yes, while not all vehicles have ABS, its obvious removal on vehicles where it should be fitted is a fail item.

By understanding and diligently applying these regulations and testing procedures, we can ensure that vehicles maintain the highest standards of braking performance and safety on our roads.

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