Section+4+Reading+Guide

1. Vacuum Booster Operation when air pressure is greater on one side of the diaphragm than on the other a pressure differential is created reducing braking effort 2. Charcoal Filter - The charcoal filter attracts and holds gasoline vapors and keeps fumes from entering the vaccum booster. 3. Vacuum Check Valve A one way valve allowing air to flow from the booster toward the engine. It prevents loss of vacuum when the engine is shut off. 4. Vacuum Booster Released-Position Operation 5. Vacuum Booster Applied-Position Operation as the brake pedal is depressed, the floating control valve is moved toward its seat in the power piston, away from the rear of the booster.this closes off the vacuum supply to the rear section of the housing. pressure is allowed to enter between the air valve floating control valve pressurizing the rear section. the pressure forces the power piston forward.as it does it the pushrod pushes against the hydraulic reaction plate pushing the master cylinder primary and secondary pistons forward. 6. Vacuum Booster Hold-Position Operation 7. Vacuum –Failure Mode Vacuum failure, which results in a hard pedal, may be due to a faulty check valve, a collapsed vacuum hose to the intake manifold, or an internal leak in the power booster. 8. Dual Diaphragm (Tandem)Vacuum Boosters used instead of a single large booster. much smaller than single diaphragm boosters and can do the same amount of work. they increase the total area without increasing the physical diameter of the booster. 9. Brake Assist System 10. Brake Assist System Operation -The purpose of the brake assist system is to increase the brake pressure, by using a normal amount of brake pedal force. []

11. Vacuum-Booster Operation Test Park the vehicle, turn off the engine and pump the brake pedal a few times to use up any residual vacuum in the vacuum booster. Depress the brake pedal and hold it down. Start the engine. The brake pedal should drop about 1/4 inch. If this happens, it indicates that the vacuum booster is functioning properly. 

12. Vacuum-Booster Leak Test 13. Hydraulic-System Leak Test 14. Push Rod Clearance Adjustment - The push-rod adjustment is critical for the proper operation of the braking system. If the pushrod is too long, the brakes maybe partially applied during driving. If the rod is too short, the brake pedal may have to be depressed farther down before the brakes start to work. A guage is often used to measure the position of the master cylinder piston, and then the other end of the gauge is used to determine the proper push-rod clearance. 15. Hydro-Boost Hydraulic Brake Booster 16. Hydro-Boost Operation hydro boost uses pressure created by the power steering pump to make pressing the brakes easier. they are used for a few reasons. the first is the lack of vacuum from the engine. like in a diesel. or a heavy duty gas application where the motor is under ﻿heavy load ﻿ most of the time. the second reason is space.. IE there isn't enough room for a big vacuum can to assist the brakes 17. Hydro-Boost Diagnosis check power steering fluid level check for leaks from power steering pump to hydroboost unit check power steering drive belt tension check base brake operation 18. Hydro-Boost Function Test - With the engine off, apply the brake pedal several times until the accumulator is depleted completely. Depress the service brake pedal and start the engine. The pedal should fall and then push back against the drivers foot. 19. What is Regen Braking? Through the use of the motor, force at the wheels transfers torque to the electric motor shaft. Magnets on the shaft of the motor (rotor) move past electrical coils on the stator, passing the magnetic fields of the magnets through the coils, producing electricity. The electric motor becomes a generator recharging the batteries during braking.

20. Reclaiming Energy in a Hybrid When you speed up in a hybrid you use energy and then when you slow down the wheel motors will help get some of that energy back. 21. Transferring Torque Back to the motor in a hybrid 22. Principles involved in regen braking 23. Regen Braking: Series regeneration 24. Regen Braking: Parallel regeneration -less complex because the base brakes are used along with energy recovery by the motors becoming generators. front and rear brake balance is retained because the base brakes are in use during the entire braking event 25. What are AC synchronous motors? 26. Major components of AC synchronous motors -Rotor, Slip-rings, Rotor Coils, and Permanent Magnet 27. Theory of operation of AC synchronous motors The basic difference between an induction motor and a [|synchronous AC motor] with a permanent magnet rotor is that in the latter the rotating magnetic field of the stator will impose an electromagnetic torque on the magnetic field of the rotor causing it to move (about a shaft) and a steady rotation of the rotor is produced. It is called synchronous because at steady state the speed of the rotor is the same as the speed of the rotating magnetic field in the stator. 28. Limitations of Regen Braking 29. Components involved in regen braking 30. How does the vehicle change a motor to a generator so quickly? - Inertia is the fundamental property of physics that is used to reclaim energy from the vehicle. Instead of using 100% friction brakes (base brakes), the braking torque is transferred from the wheels back into the motor shaft. One of the unique things about most electric motors is that electrical energy can be converted into mechanical energy and also mechanical energy can be converted back into electrical energy. In both cases, this can be done very efficiently. Through the use of the motor and motor controller, the force at the wheels transfers torque to the electric motor shaft. The magnets on the shaft of the motor (called the rotor--the moving part of the motor) move past the electric coils on the stator (the stationary part of the motor), passing the magnetic fields of the magnets through the coils, producing electricity. Simply stated, the electric motor(s) becomes a generator to recharge the batteries during braking. This process is called regeneration, regen, or simply "reclaiming energy." 31. Engine Design Changes Related to Regen Braking in HEV’s 32. Brake Service Precautions for Hybrid Vehicles serviceing brake pads and shoes on a hybrid is the same as a conventional vehicle but you may want to take the keys out of the vehicle so the vehicle does not engage the brakes or the driveline on its own. 33. Antilock Theory of Operation Overview controls braking to each wheel to prevent lock up and help maintain control 34. ABS and Tire Traction -Traction is the difference between the actual speed and the rate at which the tire tread moves across the road. A free rolling wheel has nearly zero tire slip while a locked wheel has 100% tire slip. 35. ABS and Tire Slip/Braking Distance On dry or wet pavement, maximum traction occurs when the tire slip is held to 15-30%. On snow or ice 20-50% is optimum. A skidding tire with 100% slip has 20-30% less traction on wet or dry conditions. The shortest stopping distance is obtained when just enough force is applied to keep tire slip in range where traction is greatest. 36. ABS and Tire Slip/Vehicle Stability The ABS system is designed to allow the vehicle to slid the tires and then release them for a stable stop. 37. ABS Limitations 38. Purpose and Function of ABS Components a. WSS b. ECU(EBTCM) c. HCU(BPMV) 39. ABS Control Pressure Stages a. Pressure Build-up(Normal Braking) b. Pressure Hold c. Pressure Decrease d. Pressure Increase(ABS Braking) 40. Brake Pedal Feedback feedback is caused by the abs brakes. the brake fluid pulses causing the brake pedal to pulsate. not normal for a vehicle to have a pulsating pedal during normal braking 41. Brake Pedal Travel Switch 42. Rear-Wheel ABS Operation - RWAL Electronic Control Unit Does the following: -Monitors the brake and 4WD switch inputs to determine whether or not to prepare for antilock braking control. -Operates the control valve assembly during antilock braking based on comparing the speed sensor signal to it’s own program stored in memory. -Detects RWAL system-related problems and takes diagnostic action. 43. Channels it is the channels for all the abs signals a. Three Channel Systems b. Four Channel Systems 44. Integral & Nonintegral Systems 45. Traction Control 46. ABS Diagnosis and Service a. Red Brake Warning Lamp Operation - A red brake warning lamp (RBWL) warns of a possible dangerous failure in the base brakes, such as low brake fluid level or low pressure in half of the hydraulic system. The red brake warning lamp will also light if the parking brake is applied and may light due to an ABS failure, such as low brake pressure on an integral system. b. Amber ABS Warning Lamp Operation comes when detected problem in the abs system

c. Visual Inspection take a close look at all of the components for damage. d. Road Test & Verify the Complaint road test the vehicle and duplicate customer complaint e. ABS Problem Diagnosis f. Hydraulic ABS Service Considerations- 1. Check service information 2. Bleeding electronic-hydraulic assembly 3. Manually bleeding ABS wheel brakes 4. Scan tool bleeding

47. Brake Bleeding ABS Most GM models have addimated bleading for the ABS which allows you to use the Tech 2.