Abstract: The brake monitoring system of the present invention monitors and measures brake adjustment and brake lining wear in vehicles employing air brakes having an "S-Cam" assembly. The S-Cam is actuated by an pneumatically driven push-rod, which rotates a cam shaft on which the S-Cam is mounted by moving a slack adjuster lever mounted on an opposed end of the cam shaft. The S-Cam forces a pair of opposed brake shoes against the interior surface of a brake drum. Rotation of the S-Cam is measured with each application of the brakes and converted into a readout of the adjustment of the brake's adjustment and brake wear which is displayed in the vehicle cab.