1942 - 1947 Chevrolet Shop Manual



	5-12

	Inspection 1. Inspect the cylinder bore, making sure that it is smooth. A scored or damaged cylinder must be replaced. 2. Check rubber cups for damage or swelling due to improper brake fluid. Replace the cups when necessary. Improper brake fluid will cause the cups to swell as much as 40 per cent. 3. Check the fit of the piston in the cylinder bore, using a feeler gauge, Fig. 27. This clearance should be from 2 to 4 thousandths of an inch. Reassembly and Replacement 1. Dip pistons and rubber cups in brake fluid. 2. Place the spring in the center of the housing, the rubber cups at each end of the spring, with their cupped sides to the spring and the flat face of the cup flush with the piston. 3. Replace the adjusting covers with the adjusting screws in place. 4. Reassemble the wheel cylinder to the flange plate, connect the wheel cylinder pipe or hose and replace the brake shoe retracting spring, brake drum, and the wheel. After a wheel cylinder has been overhauled and replaced, all hydraulic brake lines must be bled. WHEEL CYLINDER SIZES AND IDENTIFICATION Each brake has a specified wheel cylinder, depending on the brake lining area of the brake. It is important that only the specified wheel cylinder be used at that wheel. Front Rear Passenger Cars and Sedan Delivery ................,.. 1-1/4" 1-3/8" 1/2 and 3/4-Ton Truck....... . . 1-1/4" 1-3/16" 3/4-Ton Special and 3/4-Ton Long W.B. Panel............ 1-1/4" 1-3/8" 1-1/2-Ton and C.O.E. Trucks. . . 1-1/4" 1-1/2" The above sizes are stamped under the adjusting cover lock spring on each cylinder housing. The numbers stamped on the housing indicate the size of the piston. BRAKE CABLES The rear brake cables of the passenger cars are identical. However, 1-1/2-ton truck models use right and left emergency brake cables. On these models the left-hand brake cable may be identified by a string tracer woven under the cable wire shield.	On the 1/2-ton truck the emergency brake cables are longer than are the cables on any of the other models. This provides for the attachment of the cable to the pull rod at the pulleys on the frame cross member. ALCOHOL FOR CLEANING HYDRAULIC BRAKE PARTS We cannot recommend using any alcohol for cleaning the hydraulic brake system which is less than 188 per cent proof because weaker alcohols contain 10 per cent or more of water. There are some radiator anti-freezes that are even 200 per cent proof. In any case where mineral oil has gotten into the hydraulic brake system and is being flushed out with alcohol or "Declene," in order to clean out the mineral oil, it is best that the flushing should employ generous quantities of the alcohol or "Declene" and the flushing be conducted in a vigorous manner. Mineral oil is not soluble in alcohol. The two will mix mechanically, and for this reason a rather large quantity of alcohol, with considerable pressure behind it, must be used. Alcohol or "Declene" that has been used for cleaning out a system containing some mineral oil should never be used again. SERVICING VACUUM POWER BRAKES In modern truck operation where heavy loads and higher speeds are encountered, safety has become one of the most important factors on the heavier types of equipment. A heavily loaded truck cannot be stopped as easily as one with a light load by physical effort alone. Therefore, we employ the use of an additional force to aid the driver in brake application. The Vacuum Power Brake is installed to make available to the driver a greater pressure than he could possibly exert by his foot pressure on the brake pedal. This greatly increases the driver's ability to stop quickly when heavily loaded or driving at high speeds. In other words, the Vacuum Power Brake is an auxiliary power unit that applies additional force to the hydraulic main cylinder piston. Because of the increasing use of Vacuum Power Brakes, the well-informed service man must understand their servicing. The servicing of the Vacuum Power Brakes will not be difficult if the service man will closely follow instructions. However, it is well to remember that proper care of the unit is a guarantee for its longer life and satisfactory operation. NOTE—The service instructions apply to both the Conventional and Cab-Over-Engine Trucks.