HEAVY TRUCK BRAKES MICHIGAN MECHANIC STUDY GUIDE
AN ENGINE BRAKE (JACOBS BRAKE)
A. IS A SELF-ENERGIZING SERVO TYPE.
B. IS NORMALLY USED IN PLACE OF A SPRING BRAKE.
C. RESTRICTS THE INTAKE PORT AND CAUSES A BUILD UP OF 30-45 LBS OF PRESSURE.
D. OPENS THE EXHAUST VALVES NEAR THE TOP OF THE COMPR...
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HEAVY TRUCK BRAKES MICHIGAN MECHANIC
STUDY GUIDE
AN ENGINE BRAKE (JACOBS BRAKE)
A. IS A SELF-ENERGIZING SERVO TYPE.
B. IS NORMALLY USED IN PLACE OF A SPRING BRAKE.
C. RESTRICTS THE INTAKE PORT AND CAUSES A BUILD UP OF 30-45 LBS OF PRESSURE.
D. OPENS THE EXHAUST VALVES NEAR THE TOP OF THE COMPRESSION STROKE TO RELEASE THE
COMPRESSED AIR. (CORRECT AWNSER)
IN THE SYSTEM SHOWN BELOW, THE PART AT C IS:
A. AN INVERSION VALVE. (POSSIBLE CORRECT AWNSER)
B. A SAFETY VALVE.
C. A MODULATOR VALVE. (NOT CORRECT AWNSER)
D. A RELAY VALVE.
A MECHANIC HAS REMOVED A BRAKE DRUM AND FOUND THE BRAKE LININGS SOAKED WITH GREASE.
THE BRAKE LININGS SHOULD BE:
A. REPLACED. (CORRECT AWNSER)
B. SANDED TO ROUGHEN UP THE FRICTION SURFACE.
C. DIPPED IN LACQUER THINNER.
D. WASHED WITH DENATURED ALCOHOL.
IN THE DRAWING BELOW, THE PARKING BRAKES ARE APPLIED BY:
A. AIR PRESSURE AT POINT F.
B. VACUUM IN AREA B.
C. SPRING AT POINT C.
D. PRESSURE IN AREA A. (NOT CORRECT AWNSER)
WHAT IS THE PURPOSE OF A VACUUM BOOSTER?
A. TO DECREASE BRAKE PEDAL EFFORT. (POSSIBLE CORRECT AWNSER)
B. TO PREVENT FADE UNDER HEAVY BRAKING.
C. TO PROVIDE ASSISTANCE WHEN THE ENGINE VACUUM IS LOW. (NOT CORRECT AWNSER)
D. TO MAINTAIN UNIFORM PEDAL TRAVEL AS THE LININGS WEAR.
THE TRAILER BRAKES DO NOT WORK. THE TRACTOR SYSTEM IS AT NORMAL PRESSURE. THERE ARE NO
LEAKS AND THE SERVICE AND EMERGENCY LINES ARE HOOKED UP RIGHT. WHAT COULD CAUSE THIS
PROBLEM?
A. ICE IN THE LINES AT THE TRAILER.
B. A BAD RELAY VALVE.
C. A BAD SAFETY RELIEF VALVE.
D. BOTH A AND B. (CORRECT AWNSER)
THE RESIDUAL VALVE IN THE MASTER CYLINDER:
A. LIMITS PRESSURE BUILD UP IN THE SYSTEM.
B. STOPS THE FLOW TO DAMAGED BRAKE LINES.
C. KEEPS SOME PRESSURE IN THE SYTEM WHEN THE BRAKES ARE RELEASED. (CORRECT AWNSER)
D. IS OPERATED BY ENGINE VACUUM.
HIGHER THAN NORMAL AIR PRESSURE WOULD LIKELY BE CAUSED BY:
, A. A GOVENOR THAT IS BAD OR OUT OF ADJUSTMENT. (POSSIBLE CORRECT AWNSER)
B. A PLUGGED SAFETY VALVE. (NOT CORRECT AWNSER)
C. A ONE-WAY CHECK VALVE STUCK OPEN.
D. A STICKY QUICK RELEASE VALVE.
IF GLADHAND 2 IS UNHOOKED OR HAS A SEVERE LEAK, WHAT WILL HAPPEN DURING OPERATION?
A. VALVE AT A WILL PROTECT THE PRESSURE IN THE DRY TANK.
B. TRACTOR BRAKES WILL APPLY AUTOMATICALLY. (NOT CORRECT AWNSER)
C. VALVE AT C WILL APPLY TRAILER BRAKES.
D. VALVE AT B WILL APPLY TRAILER BRAKES.
DURING A HARD STOP, ONE BRAKE HAS LOCKED ON A TRAILER WITH "S" CAM BRAKES. THE SERVICE
AND EMERGENCY LINES ARE HOOKED UP PROPERLY AND THE SYSTEM IS AT NORMAL PRESSURE BUT
THE BRAKES WILL NOT RELEASE. WHAT IS THE LIKELY CAUSE OF THIS PROBLEM?
A. THE SERVICE BRAKE CHAMBER DIAPHRAGM HAS SPLIT. (POSSIBLE CORRECT AWNSER)
B. THE CAM HAS ROLLED OVER DUE TO TOO MUCH LINING WEAR.
C. THE ANTI-LOCK MODULE HAS BURNED OUT AT THE SENDING UNIT. (NOT CORRECT AWNSER)
D. THE CHAMBER SPRING HAS RUSTED AND IS BROKEN.
TOO MUCH EFFORT IS REQUIRED ON THE BRAKE PEDAL TO STOP A TRUCK WITH A VACUUM
BOOSTER. WHAT IS THE LIKELY CAUSE OF THIS PROBLEM?
A. SEIZED AUTOMATIC ADJUSTERS.
B. GLAZED LININGS
C. A DEFECTIVE MODULATOR VALVE. (NOT CORRECT AWNSER)
D. VERY HIGH ENGINE VACUUM. (POSSIBLE CORRECT AWNSER)
WITH THE VALVE PICTURED BELOW, THE OPERATOR CAN:
A. APPLY THE TRACTOR BRAKES BY SPRING PRESSURE. (NOT CORRECT AWNSER)
B. APPLY THE TRAILER BRAKES BY AIR PRESSURE.
C. ENGAGE OR DISENGAGE THE PARKING BRAKES.
D. APPLY THE TRAILER BRAKES BY SPRING PRESSURE.
IT IS FOUND THAT THE RUBBER DIAPHRAGM IN A MASTER CYLINDER COVER IS SWOLLEN TO NEARLY
DOUBLE IN SIZE. THIS COULD BE CAUSED BY:
A. CONTAMINATION OF THE BRAKE FLUID WITH ENGINE OIL. (POSSIBLE CORRECT AWNSER)
B. ACCIDENTAL MIXING WITH SILICONE BRAKE FLUID.
C. MOISTURE IN THE BRAKE FLUID.
D. ALL OF THE ABOVE. (NOT CORRECT AWNSER)
WITH THE ENGINE STOPPED, A MECHANIC HOLDS THE POWER BRAKE PEDAL IN THE DEPRESSED
POSITION. THE MECHANIC THE STARTS THE ENGINE WITH THE PEDAL STILL DEPRESSED. THE PEDAL
SINKS SLIGHTLY. WHAT DOES THIS INDICATE?
A. THE BRAKE BOOSTER IS SATISFACTORY. (CORRECT AWNSER)
B. A LEAKING CHECK VALVE.
C. A TORN DIAPHRAGM.
D. A DEFECTIVE CONTROL VALVE ASSEMBLY.
A MECHANIC FINDS GEAR LUBE INSIDE BOTH BRAKE DRUMS ON A DRIVING AXLE. WHAT IS THE MOST
LIKELY CAUSE OF THIS PROBLEM?
A. A BAD PINION SEAL.
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