T4 ASE BRAKES QUESTIONS AND
ANSWERS
Psi09loss09rate09for09Straight09Truck09-09ans--✔✔209psi/minute
Psi09loss09rate09for09combination09vehicle09-09ans--✔✔less09than09309psi/minute
Service09Brake09Pressure09Drop09Test09-09ans--
✔✔Apply09service09brake09to099009psi.09Loss09rate09should09be09less09than09309psi/
minute09for09straight09vehicles09and09less09than09409psi/
minute09for09combination09vehicles.
Improperly09adjusted09brake09shoes09-09ans--✔✔Cause
1)09brake09imbalance
2)09increased09stopping09distance
3)09excessive09heat09and09wear
Instability09and09premature09wear09-09ans--
✔✔a09409psi09difference09in09the09air09delivery09between09axles09is09enough09to09cau
se09instability09and09premature09wear.
Troubleshooting09poor09brake09performance09due09to09air09-09ans--
✔✔1)09inspect09air09compressor
2)09verify09pressure09build09up
3)09look09for09clogged09air09compressor09filter
4)09possible09slipping09belt
5)09possible09air09leaks
6)09possible09defective09governor
Pressure09Governors09-09ans--✔✔1)09regulates09air09going09to09system
2)09adjustable09pressure
3)09defective09governor09or09out09of09adjustment09can09cause09compressor09to09functi
on09improperly.09
4)09designed09to09regulate09the09compressors09output.
5)09may09be09attached09to09compressor09or09externally09mounted.
, Air09Compressors09-09ans--
✔✔1)09Power09is09transferred09to09the09air09compressor09by09either09an09internal09ge
ar09or09by09an09external09belt.09Belt09is09most09common.
2)air09can09be09drawn09directly09from09the09atmosphere09through09a09filter.
3)09Pistons09push09the09air09through09a09discharge09valve09to09the09supply09reservoir.
Supply09Reservoir09"Wet09Tank"09-09ans--
✔✔1)09tank09closest09to09the09compressor.09
2)09"pop09off09valve"09located09on09this09tank09to09keep09from09over09pressuring09the0
9system.
Pop-off09valve09-09ans--
✔✔Also09known09as09the09pressure09relief09valve,09exhaust09valve,09adjustable09pres
sure09limiting09(APL)09valve,09or09overflow09valve;09this09valve09is09the09point09of09exit
09of09excessive09pressure09buildup09before09damaging09air09components.
Manual09and09Automatic09Drain09Valves09-09ans--
✔✔1)09installed09in09each09reservoir/
tank09to09help09purge09the09system09from09moisture.
2)Used09in09high09humid09or09wet09climates.
3)09manual09drain09valves09should09be09drained09on09a09daily09basis
Air09Dryer09-09ans--
✔✔1)09used09to09keep09condensation09out09of09the09system09using09a09desiccant09m
aterial09to09remove09moisture.
2
Air09Compressor09troubleshooting09-09ans--
✔✔1)09can09develop09air09leaks09and09pass09oil09into09the09brake09system09which09wi
ll09cause09poor09braking09and09or09grabbing09or09dragging.09
2)09clogged09air09intake09filter09will09cause09slow09pressure09build09up.
Compressor09oil09checks09-09ans--
✔✔1)09engine09oil09should09be09checked09for09compressors09that09get09lubrication09fr
om09engine.09
2)09Oil09sump09compressors09have09their09own09oil09reservoirs09and09should09be09che
cked09daily.
ANSWERS
Psi09loss09rate09for09Straight09Truck09-09ans--✔✔209psi/minute
Psi09loss09rate09for09combination09vehicle09-09ans--✔✔less09than09309psi/minute
Service09Brake09Pressure09Drop09Test09-09ans--
✔✔Apply09service09brake09to099009psi.09Loss09rate09should09be09less09than09309psi/
minute09for09straight09vehicles09and09less09than09409psi/
minute09for09combination09vehicles.
Improperly09adjusted09brake09shoes09-09ans--✔✔Cause
1)09brake09imbalance
2)09increased09stopping09distance
3)09excessive09heat09and09wear
Instability09and09premature09wear09-09ans--
✔✔a09409psi09difference09in09the09air09delivery09between09axles09is09enough09to09cau
se09instability09and09premature09wear.
Troubleshooting09poor09brake09performance09due09to09air09-09ans--
✔✔1)09inspect09air09compressor
2)09verify09pressure09build09up
3)09look09for09clogged09air09compressor09filter
4)09possible09slipping09belt
5)09possible09air09leaks
6)09possible09defective09governor
Pressure09Governors09-09ans--✔✔1)09regulates09air09going09to09system
2)09adjustable09pressure
3)09defective09governor09or09out09of09adjustment09can09cause09compressor09to09functi
on09improperly.09
4)09designed09to09regulate09the09compressors09output.
5)09may09be09attached09to09compressor09or09externally09mounted.
, Air09Compressors09-09ans--
✔✔1)09Power09is09transferred09to09the09air09compressor09by09either09an09internal09ge
ar09or09by09an09external09belt.09Belt09is09most09common.
2)air09can09be09drawn09directly09from09the09atmosphere09through09a09filter.
3)09Pistons09push09the09air09through09a09discharge09valve09to09the09supply09reservoir.
Supply09Reservoir09"Wet09Tank"09-09ans--
✔✔1)09tank09closest09to09the09compressor.09
2)09"pop09off09valve"09located09on09this09tank09to09keep09from09over09pressuring09the0
9system.
Pop-off09valve09-09ans--
✔✔Also09known09as09the09pressure09relief09valve,09exhaust09valve,09adjustable09pres
sure09limiting09(APL)09valve,09or09overflow09valve;09this09valve09is09the09point09of09exit
09of09excessive09pressure09buildup09before09damaging09air09components.
Manual09and09Automatic09Drain09Valves09-09ans--
✔✔1)09installed09in09each09reservoir/
tank09to09help09purge09the09system09from09moisture.
2)Used09in09high09humid09or09wet09climates.
3)09manual09drain09valves09should09be09drained09on09a09daily09basis
Air09Dryer09-09ans--
✔✔1)09used09to09keep09condensation09out09of09the09system09using09a09desiccant09m
aterial09to09remove09moisture.
2
Air09Compressor09troubleshooting09-09ans--
✔✔1)09can09develop09air09leaks09and09pass09oil09into09the09brake09system09which09wi
ll09cause09poor09braking09and09or09grabbing09or09dragging.09
2)09clogged09air09intake09filter09will09cause09slow09pressure09build09up.
Compressor09oil09checks09-09ans--
✔✔1)09engine09oil09should09be09checked09for09compressors09that09get09lubrication09fr
om09engine.09
2)09Oil09sump09compressors09have09their09own09oil09reservoirs09and09should09be09che
cked09daily.
