ASE T4 Brakes (Medium/Heavy Truck) study plan

Trace the full air supply path from compressor through governor, reservoirs, and drain valves, and describe what each component does to pressure and moisture

Explain governor cut-in and cut-out operation and predict gauge behavior when cut-out pressure is set too high or too low

Identify the function of the safety valve, check valve, and low-pressure warning switch and state the failure symptom for each

Describe the alcohol evaporator or air dryer cycle and the effect of a saturated desiccant on system pressure build time

Trace the service brake circuit from treadle valve to relay valve to brake chambers and explain the relay valve's role in reducing lag time

Differentiate straight truck, tractor, and trailer service and emergency circuit layouts and state where each protection valve sits

Diagnose a slow pressure build, a fast pressure loss, and a stuck-cut-in governor by listing the first three checks for each

Describe the standard static leak-down test procedure and the acceptable pressure loss limits for an unapplied and applied system

Identify slack adjuster, chamber, pushrod, and foundation brake components on a typical S-cam assembly and state the adjustment limit for pushrod stroke

Explain automatic slack adjuster operation and describe why an auto slack that is out of adjustment indicates a foundation brake problem rather than an adjuster problem

Describe the procedure for measuring applied pushrod stroke and the conditions under which the measurement is invalid

Compare drum and disc foundation brakes on heavy trucks in terms of adjustment, inspection points, and common wear patterns

Explain the ABS wheel speed sensor, ECU, and modulator valve relationship and the effect of a single failed sensor on system behavior

Describe how to retrieve and interpret ABS blink codes and what each typical code group points to

Explain Automatic Traction Control operation, including the role of the engine and retarder interface, and how ATC differs from ABS in actuation

Diagnose a wheel-end ABS fault by ordering the checks from sensor air gap to tone ring to wiring to modulator

Identify the components of a hydraulic brake system on a medium truck, including master cylinder, proportioning valve, metering valve, combination valve, and residual check valve

Explain the difference between a bleeding sequence for a front-rear split system and a diagonal split system and state the reason for each order

Diagnose a low or spongy pedal by separating fluid loss, air in the system, and a bypassing master cylinder into distinct test results

Describe the inspection criteria for a brake hose, caliper slide, and rotor or drum surface that would trigger replacement rather than reuse

Describe bench bleeding and on-vehicle bleeding of a master cylinder and state the failure that results from skipping bench bleeding

Explain the function of a residual pressure valve and differentiate the value used for drum versus disc circuits

Identify parking brake system types on medium and heavy trucks, including spring brake chambers, driveline parking brakes, and air-applied park valves

Explain spring brake chamber operation and the correct and safe procedure for caging a spring brake before service

Explain the correct adjustment and inspection of a spring brake pushrod and the test that confirms the park brake holds

Describe the procedure for inspecting, repacking, and adjusting a wheel bearing assembly, including the correct end play or preload target check

Identify the seals in a wheel-end assembly and explain how an overfilled or underfilled hub produces a specific leak or wear pattern

Diagnose a wheel-end oil leak by distinguishing an inner seal failure from a vent or plug problem and from a bearing adjustment problem

Re-rank all four domains by your measured practice-test score and rebuild a weakness list ranked by points left on the table

Re-derive the leak-down limits, pushrod stroke limits, and spring brake caging steps without notes

Work through fifteen mixed scenario questions that combine a symptom in one domain with a root cause in another

Consolidate every missed practice item into a single corrected-rule sheet and recite it once