1942 - 1947 Chevrolet Shop Manual



	*5-14*

	Testing for Leakage 1. Remove the pipe plug from the front end of the power cylinder and attach a vacuum gauge at this point. 2. Start the engine and note the vacuum gauge reading, which should show between 16 and 20 inches of vacuum. (Fig. 31.) 3. Stop the engine. If the vacuum gauge shows a rapid falling off, leakage is indicated which may be in the power cylinder, check valve, or vacuum line to the intake manifold.	If this is the case, the check valve should be removed, disassembled, and cleaned. The vacuum line and connection should be inspected and tightened and damaged hoses replaced. Then make another test to make sure the leak has been corrected.


		Fig. 32—Vacuum Gauge Hook-Up far Checking Vacuum Line and Check Valve for Air Leaks Power Cylinder If from the previous test the leak is found to be in the power cylinder, it should be lubricated as instructed under "Lubrication." Then another test should be made to make sure the trouble has been corrected. ADJUSTMENTS Brake Valve The brake valve must be checked for correct adjustment when any tests of the system have been made. Accurate valve adjustment is a very important item in servicing reactionary power cylinders. Care must be exercised in this operation and proper methods used if satisfactory results are to be expected. Valve adjustment must be made with the engine running at idling speed. A special bushing is used to make the valve adjustment. This bushing is easily made up from brass or steel, to the dimensions shown in Fig. 33,
	Fig. 31— Checking Braking System far Air Leaks Testing Vacuum Line and Check Valve 1. Disconnect the vacuum hose at the power cylinder and attach the vacuum gauge to the end of the hose. Fig. 32. 2. Start the engine and note the vacuum gauge reading, which should show between 16 to 20 inches of vacuum. 3. Stop the engine. If the vacuum is retained for a reasonable length of time, the check valve and vacuum line are OK, indicating that the leak is in the power cylinder. However, if the gauge should show a rapid falling off, then the leakage is indicated in the check valve or vacuum line.

		Fig. 33—Vacuum Valve Adjusting Bushing