Air passes through. If the non-return valve is defective, install a new non -return valve and repeat the vacuum leak test. If the nonreturn valve is OK, the Servo is leaking. Replace the Servo with a new kit. If the applications are Servo assisted, there is no vacuum leak. If the applications are not servo assisted, disconnect the vacuum hose from the non-return valve. Then attach a short length of hose to the valve. Blow air through the hose. The valve is defective if. BRAKE_DIESEL 30
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