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3.6
Hydraulic Air and Vacuum Systems
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| Method of Inspection | Reason for rejection |
| A. Leaks | |
| 1.
Check for leaks in any part of the braking system, with and
without the brakes being applied. Note: For vehicles fitted with vacuum servo or power operated brakes, the engine must be idling during these inspections. Note: On some vehicles, a complete inspection of the service brake system requires the bonnet to be opened. |
1. A leak in any part of a braking system. |
| B. Brake Pipes and Flexible Hoses | |
| 1. Check that rigid brake pipes are securely held and not free to vibrate. | 1. A rigid brake pipe inadequately clipped or otherwise supported. |
| 2. Check all accessible rigid brake pipes for | |
| a. fouling by a moving part | a. fouled by moving parts |
| b. kinks | b. kinked |
| c. chafing, corrosion and damage Note: To assess correctly the condition of corroded metal pipes, surface dirt might have to be removed. This might require light scraping with the Corrosion Assessment Tool ‘spade end’. Care must be taken not to damage any protective coating. |
c. excessively chafed, corroded or damaged Note: Chafing, corrosion of, or damage to, a rigid brake pipe so that its wall thickness is reduced by 1/3 (eg approximately 0.25mm for typical hydraulic brake pipe) is a reason for rejection |
| d. repairs |
d. inadequately repaired or with unsuitable joint fittings Note: Repairs to the pressure lines of hydraulic brake systems are unacceptable unless suitable connectors are used. Compression joints of a type using separate ferrules are not suitable |
| 3. Examine flexible hoses for signs of weakness under pressure with foot-brake fully applied. | 3. A flexible hose bulging under pressure. |
| 4. Examine all flexible hoses for | 4. A flexible hose |
| a. room to move as necessary without fouling any part of vehicle | a. has insufficient room to move, resulting in fouling on any part |
| b. kinks | b. kinked |
| c. stretching or twisting | c. stretched or twisted |
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d. chafing or deterioration Note: A hose should be rejected for cracking or chafing only if that is sever enough to expose the reinforcement. |
d. excessively chafed or deteriorated |
| e. exposure to excessive heat | e. exposed to excessive heat |
| C. Hydraulic Master Cylinders and Reservoirs | |
| C.
Hydraulic Master Cylinders and Reservoirs 1. Where practicable, check hydraulic master cylinders and reservoirs for |
1. A master cylinder or reservoir |
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a. security of mounting Note: See also 3.6 D3 |
a. insecurely mounted |
| b. excessive corrosion | b. severely corroded |
| c. damage | c. damaged |
| d. presence of reservoir cap | d. with a reservoir cap missing |
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e. fluid level Note: This check is confined to transparent reservoirs or where an indicator is fitted. Reservoir caps should not be removed |
e. has dangerously low fluid level eg significantly below the minimum level indication when this is shown |
| f. leaks | f. leaking hydraulic fluid |
| D. Servos | |
| D. Servos | 1. A servo |
| 1. Check servos for | |
| a. security of mounting | a. insecurely mounted |
| b. excessive corrosion | b. excessively weakened by corrosion |
| c. damage | c. damaged to the extent that its function is impaired |
| d. vacuum pipe deteriorated, kinked, split, collapsed, excessively chafed | d. vacuum pipe deteriorated, kinked, split, collapsed, excessively chafed |
| e. leaks | e. leaking |
| 2. Where an adjustment indicating rod is provided, check if brake adjustment is necessary | 2. Adjustment indicating rod shows brake adjustment is necessary |
| 3. Examine the condition of chassis or body structure and panelling around the master cylinder or combined master cylinder/servo mounting. | 3. Deliberate modification which significantly reduces the original strength, excessive corrosion, severe distortion, a fracture or an inadequate repair of a load bearing member or its supporting structure or panelling within 30cm of the master cylinder/servo mounting, that is, within a ‘prescribed area’, see Appendix C. |
| E. Reservoirs (Air/Vacuum) | |
| (Including accumulators, pressure and vacuum vessels). | |
| 1. Examine reservoirs for | 1. A reservoir |
| a. security of mounting | a. insecurely mounted |
| b. structural damage | b. structurally damaged (eg angled dents) |
| c. excessive corrosion | c. excessively corroded |
| 2. Check reservoir mountings and securing straps | 2. Reservoir mountings and securing straps |
| a. are free from cracks, fractures and excessive corrosion | a. cracked, fractured or excessively corroded |
| b. do not chafe the reservoir or other fittings | b. chafing reservoir or other fittings |
| 3. Check that the reservoir capacity is not unduly reduced by deformation. | 3. A significant reduction in reservoir capacity as a result of deformation. |
| F. Valves | |
| F. Valves | 1. A valve |
| 1. Examine all valves for | |
| a. security of mounting | a. insecurely mounted |
| b. damage and corrosion | b. damaged or excessively weakened by corrosion |
| 2. Check for excessive discharge of oil from a pedal exhaust valve, unloader valve and/or governor valve, quick-release valve etc | 2. Excessive discharge of oil from a valve |
| 3. Check that a load sensing valve is present and connected, if it is a standard item. | 3. Evidence that a load sensing valve has been removed or disconnected from a vehicle where it is known to have been fitted as standard. |
| 4. Check the condition of the load sensing valve and, where appropriate, its operating linkage. | 4. Load sensing valve with seized or defective linkage or obviously incorrectly adjusted. |
| G. Air Brake Actuators | |
| G. Air Brake Actuators | |
| 1. Check each brake cylinder/actuator for security, damage, corrosion and operation | 1. A cracked, damaged, insecure, inoperative or excessively corroded actuator. |
| 2. Check that all retaining and locking devices are secure. | 2. An actuator retaining or locking device insecure. |
| 3. Check the travel of operating pistons/diaphragm mechanisms. | 3. Excessive travel of the operating mechanism indicating need for adjustment. |
| H. Pumps and Compressors | |
| 1. Check the security of the vacuum pump or air compressor. | 1. A vacuum pump or air compressor insecure. |
| 2. Check the condition of the vacuum pump or air compressor drive system. | 2. A drive system missing or defective. |
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Reproduced from the MOT Inspection Manual by kind permission of THE VEHICLE INSPECTORATE.
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