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ASE H3 Drive Train (Transit Bus) study materials
ASE H3 Drive Train (Transit Bus) study resources

ASE H3 Drive Train (Transit Bus) practice questions

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Question 1Drive Train Diagnosis and Repair

On a transit bus with a hydraulically released spring parking brake, what actually holds the vehicle stationary when the parking brake is applied and air pressure is lost?

  1. A hydraulic check valve in the brake line
  2. An air-operated wedge in the wheel cylinder
  3. A spring-loaded actuator chamber Correct answer.
  4. A mechanical pawl in the transmission

Explanation

Spring brakes use a large coil spring to apply the service brake when air pressure is released or lost, making them fail-safe. Air pressure compresses the spring to release the brake during normal operation.

Question 2Drive Train Diagnosis and Repair

A bus equipped with an automatic transmission reports a harsh engagement when shifted from neutral to drive at idle. Which condition is the most likely cause?

  1. High idle speed Correct answer.
  2. Worn transmission mount
  3. Low engine idle speed
  4. Faulty reverse solenoid

Explanation

Excessive engine idle speed raises the hydraulic pressure and torque available at engagement, producing a harsh shift. Idle speed should be checked against specification before internal transmission diagnosis.

Question 3Drive Train Diagnosis and Repair

What is the primary purpose of the driveline center support bearing on a bus with a two-piece propeller shaft?

  1. To absorb engine torsional vibration
  2. To lock the shaft during parking
  3. To carry shaft weight and control whip Correct answer.
  4. To multiply torque to the rear axle

Explanation

The center support bearing supports the midsection of a long two-piece shaft, controlling whipping and vibration. It does not change torque or act as a parking device.

Question 4Drive Train Diagnosis and Repair

A bus with a rear axle differential has a pinion seal leaking gear oil onto the yoke. What should be verified before replacing the seal?

  1. That the pinion bearing preload is correct
  2. That the ring gear backlash is zero
  3. That the axle breather is clear Correct answer.
  4. That the differential is overfilled

Explanation

A clogged breather pressurizes the housing and forces oil past the seal, so it must be checked first. Replacing the seal without correcting a blocked breather leads to repeat failure.

Question 5Drive Train Diagnosis and Repair

In a bus automatic transmission, what does the torque converter stator one-way clutch do during vehicle acceleration from a stop?

  1. It redirects fluid to multiply engine torque Correct answer.
  2. It locks the converter for zero slip
  3. It releases to allow free turbine spin
  4. It disengages the oil pump

Explanation

The stator is held by its one-way clutch during acceleration so it redirects fluid from the turbine back to the pump, multiplying torque. At coupling speed the stator freewheels to avoid restricting flow.

Question 6Drive Train Diagnosis and Repair

A transit bus exhibits a vibration that increases with road speed and is felt through the floor, disappearing when the driveline is disconnected and the engine is run. What is the most probable cause?

  1. Driveline imbalance Correct answer.
  2. Wheel bearing end play
  3. Brake drum runout
  4. Engine misfire at idle

Explanation

A speed-related vibration that disappears when the driveline is isolated points to the propeller shaft or its joints, commonly imbalance. Engine-driven vibration would persist with the driveline disconnected.

Question 7Drive Train Diagnosis and Repair

What is the correct action when a universal joint on a bus propeller shaft shows needle bearing spalling and a brinelled trunnion?

  1. Shim the bearing caps
  2. Repack the joint with grease
  3. Replace the complete U-joint Correct answer.
  4. Rotate the shaft 180 degrees

Explanation

Brinelling and spalling indicate the hardened surfaces are damaged and cannot be restored by greasing or shimming. The joint must be replaced to restore service life.

Question 8Drive Train Diagnosis and Repair

On a bus with an electronically controlled automatic transmission, a fault code for output speed sensor signal loss is stored. Which symptom is most directly expected?

  1. Engine will not crank
  2. No reverse gear only
  3. Erratic or default shift scheduling Correct answer.
  4. Converter clutch always engaged

Explanation

The output speed signal is used for shift scheduling and ratio calculation, so its loss typically causes erratic shifts or a default schedule. Other functions such as cranking are not controlled by this sensor.

Question 9Drive Train Diagnosis and Repair

A bus automatic transmission slips in second gear but holds firmly in first and third. Which component is the most likely cause?

  1. Second gear apply clutch pack Correct answer.
  2. Reverse band servo
  3. Output shaft speed sensor
  4. Torque converter stator clutch

Explanation

A slip confined to one gear points to the clutch or band that applies only in that gear. Since first and third hold, the shared components and the converter are functioning.

Question 10Drive Train Diagnosis and Repair

During a stall test on a bus automatic transmission, engine speed is significantly higher than specification in all ranges. What does this indicate?

  1. Converter clutch slipping
  2. An internal transmission slip Correct answer.
  3. Engine performance problem
  4. Converter stator freewheeling

Explanation

High stall speed across all ranges indicates the transmission cannot hold the engine, typically from internal clutch or band slip or low line pressure. Engine performance faults would produce low stall speed.

Question 11Drive Train Diagnosis and Repair

A bus with a two-piece driveshaft has a vibration at 55 mph that changes when the shaft is rotated one spline. What is the most appropriate diagnosis?

  1. Faulty wheel speed sensor
  2. Worn differential side gears
  3. Driveline balance or phasing error Correct answer.
  4. Excessive pinion bearing preload

Explanation

A vibration that changes with shaft index position indicates imbalance or improper yoke phasing. Correct phasing places the universal joint yokes in line and balance weights in the correct plane.

Question 12Drive Train Diagnosis and Repair

A bus axle has a leaking wheel seal on a full-floating rear axle. What is the correct first step in diagnosis?

  1. Resurface the brake drum
  2. Replace the wheel bearing
  3. Verify the axle vent is unobstructed Correct answer.
  4. Increase the lubricant level

Explanation

A blocked vent pressurizes the housing and pushes lubricant past the seal, so vent function must be verified before seal replacement. This prevents repeat seal failure.

Question 13Drive Train Diagnosis and Repair

A bus automatic transmission has a delayed engagement into drive when cold, improving when warm. Which condition best explains this?

  1. Excessive governor pressure
  2. Worn output shaft bearing
  3. Faulty shift solenoid
  4. Low fluid level or aerated fluid Correct answer.

Explanation

Low or aerated fluid causes delayed engagement that improves as the fluid warms and expands or de-aerates. Fluid level and condition should be checked before internal diagnosis.

Question 14Drive Train Diagnosis and Repair

A bus with an automatic transmission has a shudder during light-throttle converter clutch apply. What is the most likely cause?

  1. Incorrect tire pressure
  2. Low engine coolant temperature
  3. Worn converter clutch friction surface Correct answer.
  4. Faulty reverse solenoid

Explanation

Shudder during lockup application often comes from a worn or glazed converter clutch lining or contaminated fluid. The apply strategy should be verified before condemning the converter.

Question 15Drive Train Diagnosis and Repair

A bus with an automatic transmission has a slip in reverse but firm engagement in all forward ranges. Which component should be inspected first?

  1. Reverse band or reverse clutch Correct answer.
  2. Torque converter stator
  3. Forward clutch pack
  4. Output shaft bearing

Explanation

Since forward ranges are firm, the fault is isolated to the element that applies only in reverse, typically the reverse band or reverse clutch. Forward clutches and the converter are common to forward operation.

Question 16Drive Train Diagnosis and Repair

On a transit bus, which component transfers engine torque to the transmission input shaft while allowing the engine to idle with the bus stopped in gear?

  1. The torque converter Correct answer.
  2. The differential pinion
  3. The clutch release bearing
  4. The output shaft governor

Explanation

A torque converter uses hydraulic coupling between the impeller and turbine to multiply and transmit torque while permitting slip at idle. That slip is what lets the engine idle with the bus held stationary in a drive range.

Question 17Drive Train Diagnosis and Repair

What is the function of the differential in a transit bus rear axle?

  1. To multiply engine torque before it reaches the transmission
  2. To allow the rear wheels to turn at different speeds while delivering torque to both Correct answer.
  3. To lock both rear wheels together at all times
  4. To hold the axle shafts in alignment during cornering

Explanation

The differential divides torque to both axle shafts while permitting a speed difference between them, which is required because the outer wheel travels a longer path in a turn.

Question 18Drive Train Diagnosis and Repair

A bus propeller shaft is installed with its universal joint yokes out of phase. What symptom should the technician expect?

  1. A hard shift into reverse only
  2. A pulsation felt only when the brakes are applied
  3. A steady drop in engine oil pressure
  4. A speed-related vibration that is present in all gears Correct answer.

Explanation

Universal joints must be phased so their angular velocity fluctuations cancel; when yokes are misaligned the shaft produces a cyclic vibration that rises with driveshaft speed.

Question 19Drive Train Diagnosis and Repair

Which lubricant is normally specified for a bus rear axle differential assembly?

  1. Gear oil meeting the manufacturer's API service category for hypoid axles Correct answer.
  2. Automatic transmission fluid
  3. Engine oil of the viscosity used in the engine
  4. Chassis grease packed into the housing

Explanation

Hypoid ring and pinion gears experience high sliding loads and require extreme-pressure gear lubricant of the correct service category and viscosity.

Question 20Drive Train Diagnosis and Repair

What is the primary purpose of the slip joint on a bus propeller shaft?

  1. To allow changes in shaft length as the suspension moves Correct answer.
  2. To seal gear oil inside the transmission extension housing
  3. To dampen torsional vibration at high speed
  4. To provide a mounting point for the center bearing

Explanation

As the rear axle moves up and down relative to the transmission, the distance between them changes; the slip joint accommodates that change without loading the driveline.

Question 21Drive Train Diagnosis and Repair

A bus with an automatic transmission is being checked for fluid level. Which condition gives the most accurate reading?

  1. Engine off, immediately after a long highway run
  2. Engine running, transmission in neutral or park, fluid at operating temperature Correct answer.
  3. Engine off and cold, transmission in park
  4. Engine running and bus moving at road speed

Explanation

Converter-equipped automatics must be checked with the engine running so the converter and cooler are filled and the pump is circulating fluid, and at operating temperature per the manufacturer's procedure.

Question 22Drive Train Diagnosis and Repair

A bus driver reports a rhythmic clunk from underneath that is loudest during light acceleration and coast, and the propeller shaft has visible rotational play at one joint. What is the most likely cause?

  1. A worn universal joint Correct answer.
  2. A failed output speed sensor
  3. A restricted transmission cooler
  4. A misadjusted parking brake

Explanation

Rotational play plus a clunk that changes with torque reversal is the classic signature of a worn universal joint cross or bearing.

Question 23Drive Train Diagnosis and Repair

During a road test, a bus transmission shifts normally when cold but flares on the 2-3 shift when hot. Which check should be performed first?

  1. Adjust the throttle position sensor
  2. Verify fluid level and condition, then check line pressure Correct answer.
  3. Replace the torque converter
  4. Replace the valve body

Explanation

Heat-sensitive shift complaints are often caused by low or degraded fluid and by pressure that falls off when hot, so level, condition, and line pressure are the logical first checks.

Question 24Drive Train Diagnosis and Repair

What does the driveshaft center support bearing assembly include that allows the shaft to flex slightly without binding?

  1. A rubber or elastomeric cushion around the bearing Correct answer.
  2. A thrust washer at the pinion
  3. A bolted solid steel clamp
  4. A second slip yoke

Explanation

The center bearing is carried in a flexible cushion so minor driveline angles and movement are absorbed rather than transferred to the bearing and mount.

Question 25Drive Train Diagnosis and Repair

A bus rear axle shows metal particles on the drain plug magnet and a howl that rises and falls with vehicle speed. What is the most appropriate next step?

  1. Flush the housing and refill with fresh lubricant
  2. Replace the wheel seals and retest
  3. Remove the carrier and inspect the ring and pinion and bearings Correct answer.
  4. Re-torque the pinion nut and return the bus to service

Explanation

Debris on the magnet combined with a speed-related howl indicates internal gear or bearing distress that requires disassembly and inspection.

Question 26Drive Train Diagnosis and Repair

On a bus with a fully automatic transmission, what does the manual valve do when the selector is moved from neutral to drive?

  1. It energizes the torque converter clutch solenoid
  2. It mechanically locks the output shaft
  3. It opens the converter drainback valve
  4. It directs line pressure to the forward range hydraulic circuit Correct answer.

Explanation

The manual valve is linked to the shift selector and routes line pressure into the selected range's circuits, which enables the appropriate clutches and bands.

Question 27Drive Train Diagnosis and Repair

A bus exhibits a vibration only during acceleration that disappears when the throttle is released, and the driveline angles have been verified. What should be inspected next?

  1. Wheel bearing end play
  2. Engine and transmission mounts for separation or collapse Correct answer.
  3. Tire balance weights
  4. Brake drum runout

Explanation

A torque-sensitive vibration that vanishes on coast often comes from a mount that deflects under load and changes driveline alignment.

Question 28Drive Train Diagnosis and Repair

Which statement correctly describes the torque multiplication phase of a torque converter?

  1. It occurs when the turbine is turning much slower than the impeller and the stator is held Correct answer.
  2. It occurs only in reverse range
  3. It occurs only when the converter clutch is applied
  4. It occurs when the turbine speed equals the impeller speed

Explanation

With a large speed difference between impeller and turbine, fluid leaving the turbine is redirected by the held stator to add torque; as speeds equalize the multiplication drops to zero.

Question 29Drive Train Diagnosis and Repair

A bus transmission has a code for a shift solenoid circuit that is intermittent. Which test best isolates whether the fault is in the harness or the solenoid?

  1. Check transmission fluid color
  2. Measure solenoid resistance at the transmission connector and compare with a resistance check at the control module Correct answer.
  3. Replace the solenoid and clear the code
  4. Perform a stall test

Explanation

Comparing resistance at both ends of the circuit separates a harness problem from a solenoid problem, since a good solenoid reads the same at both points.

Question 30Drive Train Diagnosis and Repair

A bus axle has excessive ring gear backlash. What is the most likely consequence if the bus is returned to service uncorrected?

  1. Loss of park pawl engagement
  2. Higher transmission line pressure
  3. Impact loading and accelerated gear tooth wear Correct answer.
  4. Increased wheel bearing preload

Explanation

Excessive backlash lets the gears slap together on each torque reversal, producing impact loads that damage tooth surfaces and may lead to breakage.

Question 31Drive Train Diagnosis and Repair

What is the correct procedure for measuring differential carrier bearing preload on a bus axle during setup?

  1. Measure preload only after the axle is road tested
  2. Set preload by feel with the carrier in place
  3. Use the specified turning torque or spreader procedure from the service information Correct answer.
  4. Tighten the bearing caps to the torque used for the wheel nuts

Explanation

Preload is a measured value and must follow the manufacturer's published setup, using turning torque or a spreader gauge as specified.

Question 32Drive Train Diagnosis and Repair

A transit bus has a driveline vibration whose frequency matches tire rotation rather than shaft rotation. Which area should be investigated?

  1. Wheels and tires, including runout and balance Correct answer.
  2. Universal joint phasing
  3. Torque converter stator
  4. Transmission input shaft bearings

Explanation

Vibration tied to wheel rotation speed points to wheel and tire sources such as imbalance, runout, or a damaged tire, not to faster-spinning driveline parts.

Question 33Drive Train Diagnosis and Repair

A bus automatic transmission has a burned fluid smell and a slipping forward clutch after a prolonged heavy-load run. Which root cause is most consistent with these findings?

  1. A faulty wheel speed sensor
  2. An out-of-phase driveshaft
  3. A loose axle flange bolt
  4. Restricted cooler flow causing sustained overheating Correct answer.

Explanation

Sustained overheating degrades fluid and glazes friction material, producing both the burned smell and the slip; restricted cooler flow is a common cause of that heat.

Question 34Drive Train Diagnosis and Repair

When setting up a differential, why is pinion bearing preload established before the ring gear backlash is measured?

  1. Because backlash is measured only at the wheel flanges
  2. Because preload changes pinion position and therefore the backlash reading Correct answer.
  3. Because backlash is unaffected by pinion depth
  4. Because preload must be set with the carrier removed

Explanation

Pinion preload and depth determine where the pinion sits relative to the ring gear, so backlash must be checked only after the pinion is finally set.

Question 35Drive Train Diagnosis and Repair

What does a driveshaft critical speed refer to on a transit bus?

  1. The speed at which the governor limits vehicle speed
  2. The shaft speed at which resonant whirl can cause vibration or failure Correct answer.
  3. The torque at which the slip yoke begins to slip
  4. The maximum engine rpm permitted in first gear

Explanation

Every shaft has a rotational speed at which its natural bending frequency is excited, producing whirl; operation near that speed risks vibration and shaft failure.

Question 36Drive Train Diagnosis and Repair

Which component in an automatic transmission physically applies the holding force to a band?

  1. The pressure regulator valve
  2. The servo piston Correct answer.
  3. The accumulator spring
  4. The manual valve

Explanation

Band apply force comes from a servo piston that is pressurized by hydraulic oil to clamp the band around the drum.

Question 37Drive Train Diagnosis and Repair

A bus with a locking differential is being towed with the rear wheels on the ground. Why is this practice generally prohibited?

  1. The tires will wear unevenly
  2. The differential will overheat from lack of air flow
  3. The parking brake will not release
  4. Output shaft rotation without lubrication from the transmission pump can damage the transmission Correct answer.

Explanation

With the engine off the transmission pump is not running, so spinning the output shaft through the rear wheels can leave internal parts without lubrication.

Question 38Drive Train Diagnosis and Repair

A bus has a persistent leak at the transmission output shaft seal. What should be checked before replacing the seal?

  1. Output shaft bearing play and driveshaft runout Correct answer.
  2. Converter clutch apply voltage
  3. Engine coolant temperature
  4. Line pressure at the accumulator

Explanation

A seal will not hold if the shaft is moving off center, so bearing play and shaft runout must be ruled out before installing a new seal.

Question 39Drive Train Diagnosis and Repair

During a hydraulic pressure test, line pressure is within specification at idle but does not rise with throttle in any range. What is the most likely cause?

  1. A stuck or misadjusted throttle pressure circuit Correct answer.
  2. A worn forward clutch piston
  3. A faulty output speed sensor
  4. A leaking axle seal

Explanation

Throttle pressure should increase line pressure as load rises; if it does not, the throttle pressure signal or valve is not responding.

Question 40Drive Train Diagnosis and Repair

What is the purpose of the transmission fluid cooler on a transit bus?

  1. To remove heat that the converter and clutches add to the fluid Correct answer.
  2. To preheat the fluid for cold starts
  3. To filter metallic debris from the fluid
  4. To increase line pressure during shifts

Explanation

Torque conversion and clutch engagement generate substantial heat, and the cooler rejects that heat to keep fluid and friction materials within their limits.

Question 41Drive Train Diagnosis and Repair

What is the primary function of a transmission retarder on a transit bus?

  1. To lock the torque converter for better fuel economy
  2. To increase engine power during acceleration
  3. To provide additional braking force on long downgrades Correct answer.
  4. To preheat the transmission fluid in cold weather

Explanation

A retarder is an auxiliary braking device that uses the transmission's hydraulic system to absorb energy and slow the vehicle, reducing service brake wear on long descents.

Question 42Drive Train Diagnosis and Repair

Which component in a hydraulic retarder is responsible for absorbing the vehicle's kinetic energy?

  1. The governor
  2. The accumulator
  3. The stator
  4. The rotor Correct answer.

Explanation

In a hydraulic retarder, the rotor is driven by the driveline and churns fluid against stationary vanes, converting kinetic energy into heat.

Question 43Drive Train Diagnosis and Repair

A transit bus equipped with an automatic transmission has a retarder that is not engaging. Which of the following is the most likely cause?

  1. A disconnected retarder control valve Correct answer.
  2. A faulty brake light switch
  3. A worn transmission mount
  4. A clogged transmission filter

Explanation

The retarder is activated by a control valve that directs fluid to the retarder; if it is disconnected or faulty, the retarder will not engage.

Question 44Drive Train Diagnosis and Repair

When diagnosing a retarder that overheats the transmission fluid, which component should be inspected first?

  1. The retarder control valve
  2. The shift solenoids
  3. The torque converter
  4. The transmission cooler Correct answer.

Explanation

The retarder adds heat to the fluid; if the cooler is restricted or the fan is not working, the heat cannot be dissipated, leading to overheating.

Question 45Drive Train Diagnosis and Repair

What is the purpose of the stator in a torque converter?

  1. To provide a mounting surface for the flexplate
  2. To lock the converter clutch
  3. To redirect fluid flow to multiply torque Correct answer.
  4. To seal the converter housing

Explanation

The stator has one-way vanes that redirect fluid returning from the turbine to the impeller, multiplying torque at low speed ratios.

Question 46Drive Train Diagnosis and Repair

A bus with a torque converter clutch (TCC) has a shudder during light acceleration at highway speed. Which is the most likely cause?

  1. A damaged turbine
  2. A leaking impeller seal
  3. A worn stator
  4. A faulty TCC solenoid Correct answer.

Explanation

Shudder during TCC apply is often caused by a solenoid that is not applying the clutch smoothly or by a restricted apply circuit.

Question 47Drive Train Diagnosis and Repair

Which of the following is a primary function of the valve body in an automatic transmission?

  1. To multiply engine torque
  2. To cool the transmission fluid
  3. To direct hydraulic pressure to shift valves Correct answer.
  4. To provide a mounting point for the output shaft

Explanation

The valve body contains a network of valves that direct hydraulic pressure to apply and release clutches and bands for shifting.

Question 48Drive Train Diagnosis and Repair

A bus transmission has a delayed engagement when shifted from neutral to drive. Which component is most likely causing the delay?

  1. A misadjusted manual valve
  2. A faulty torque converter clutch
  3. A worn forward clutch piston seal Correct answer.
  4. A sticking shift solenoid

Explanation

A worn or leaking forward clutch piston seal allows pressure to bleed off, causing a delay in clutch apply when drive is selected.

Question 49Drive Train Diagnosis and Repair

What is the correct procedure for checking transmission fluid level on a bus with a dipstick?

  1. Check with the engine running in neutral and at operating temperature Correct answer.
  2. Check with the engine running in gear and at idle
  3. Check immediately after shutdown
  4. Check with the engine off and transmission cold

Explanation

Fluid level is checked with the engine running in neutral (or park) at operating temperature to ensure the converter is filled and the pump is circulating fluid.

Question 50Drive Train Diagnosis and Repair

A bus with an automatic transmission slips in all forward gears but works in reverse. Which component is most likely faulty?

  1. The reverse clutch
  2. The low/reverse band
  3. The torque converter stator
  4. The forward clutch Correct answer.

Explanation

The forward clutch is applied for all forward gears; if it slips, forward operation is affected while reverse (which uses the reverse clutch or band) may still work.