Document emG59VL4JBNwmmLeVXjK7B2w4

12 00 BRAKING SYSTEM Dual Air/Hydraulic December 1978 12 00 Page 53 D Series SERVICE AND REPAIR OPERATIONS General Precautions Before commencing any repairs or adjustments that involve tilting the cab the correct tilting procedure, described in section 44, must be strictly adhered to. WARNING: It ts dangerous not to follow the correct procedure. Brake Assemblies Brake shoes must only be changed in complete axle sets. Do not replace shoes on one side of an axle as this may cause unequal braking and result in a dangerous condition on the road. Extreme care should be taken when removing the brake shoes to avoid damage to the wheel cylinders, rubber boots or dust covers. Before installing brake assemblies clean the back plate and lightly lubricate, with high melting point grease, the steady posts, anchor or fulcrum pins, operating levers, thrust pads and the abutment edges of shoes. Hydraulic Components Before disconnecting or removing any hydraulic pipe or component the area around the connections affected should be thoroughly cleaned and, once such a disconnection is made, the exposed pipe end and connecting point must immediately be suitably sealed against the entry of dirt into the system. Before reassembly all hydraulic brake parts should be washed thoroughly in commercial alcohol, methylated spirit or approved brake fluid to ensure that all foreign matter is removed. CAUTION: Any foreign matter which finds its way into the hydraulic system may score the pistons or damage the seals and render the brakes either partly or even wholly inoperative. Do not use petrol,, paraffin, carbon tetrachloride or any other mineral oil based solvent for cleaning any part of the hydraulic system. The slightest trace of such fluids can soon render the brakes inoperative by causing swelling and deterioration of the rubber seals. Commercial alcohol or methylated spirit must always be used when flushing out the system, washing brake assemblies or their components and any container used for holding brake fluid. All cylinders, pistons arid piston seals should be protected from grease, oil and dirt during storage ahd all such parts, whether they are used or new and just drawn from stock, must be carefully examined before fitting. When inspecting seals they must not be turned inside' out as this would strain the surface skin of the rubber and lead to premature failure in service. The acceptance requirements are that the sealing lips are perfectly formed, concentric with the bore of the seal and free from knife edges, surface cracks, blemishes or other irregularities. When inspecting cylinders and pistons the acceptance requirements are that they must be free from scores, ridges, steps, sharp edges, burrs or any other imperfections in or on their working or mating surfaces. CAUTION: Any irregularity, however minute, in the seals, pistons or cylinders may form a track for fluid leakage under pressure and render the brakes inoperative: Therefore any part found to contain a visible imperfection must be rejected. It is also important that all parts are handled very carefully at all times, particularly after examination, to reduce the possibility of causing accidental scoring or other damage. Before assembling hydraulic components always immerse them in clean approved brake fluid to ease their fitting and to provide initial lubrication for the working surfaces. After completing any operation which involves the disconnection or replacement of any hydraulic component, the hydraulic system must be bled as described in operation 12 141. Asbestos WARNING: ASBESTOS OUST IS DANGEROUS TO HEALTH IF INHALED. Because of the injurious nature of asbestos dust as found in brake drums it must not be 'biown-out' with an air line. A vacuum cleaner, brush or rag must be used with care to remove any dust from brake drums. Any process which involves such requirements as cutting, filing or machining of asbestos materials must be carried out using suitable extraction equipment or with the use of a face mask or other similar personal protective equipment. Dust from any such operation should be collected in a sealed bag for disposal. Cleaning equipment to suit these conditions can be obtained from: -- B. T. Sales and Service Ltd. Huntingtower Road, Sheffield S11 7GR England. -j HFM - 005860 8006 1274