Heavy Duty Truck Systems - Chapter 29 exam questions and answers

In hydraulic disc brakes, the pads are forced against the rotors by: the pistons As the pressure of fluid received by the wheel cylinder of a drum brake system increases, which of the following happens? The wheel cylinder cups and pistons are forced apart Which of the following safety devices delays application of front disc brakes in a disc/drum system until pressure is built up in the hydraulic system? a metering valve In a typical air-over-hydraulic brake system, -depressing the treadle causes which of the -following? Air pressure is sent to the booster assemblies. Which of the following correctly describes the function of a load proportioning valve (LPV) in an air-over-hydraulic system? It increases the percentage of braking -performed by the rear axle(s) as vehicle load increases. In a hydraulic brake system, brake fluid transmits any pressure applied: equally to all parts of the enclosed circuit In a hydraulic brake system, which of the following best describes what happens when the driver s foot is applied to the brake pedal? Mechanical force is converted to hydraulic force then back to mechanical force. What component in a hydraulic brake system helps fluid in the master cylinder return back to the reservoir after a brake application? a compensating port Technician A says that in non-servo drum brakes, the forward or leading shoe is energized in normal braking when the vehicle is in forward motion. Technician B says that in non-servo drum brakes, the leading and trailing shoes exchange roles when the vehicle reverses motion. Who is correct? Both A and B In hydraulic drum brakes, the shoes are mechanically forced against the drums by: the wheel cylinders A typical TIR specification for disc rotor lateral runout would more likely be which of the following? 0.0015 inch (0.0381 mm) In a hydraulic drum brake system, what force pulls the shoes away from the drum when the brakes are released? retraction spring force at the brake shoe -assembly Which of the following devices would play a role in illuminating the brake warning light in the event of a complete hydraulic failure of the front brake circuit? pressure differential valve A typical maximum rotor thickness variation specification required by an OEM would likely be: 0.002 inch (0.0508 mm) Technician A says that when replacing disc brake pads, most OEMs recommend that fluid be removed from the master cylinder before compressing the caliper piston with a C-clamp. Technician B says that the caliper bleed screw should be opened before compressing a caliper piston with a C-clamp. Who is correct? Technician B only Which of the following best describes the -electrical operation of a typical ABS wheel speed sensor? pulse generator