EVT Chassis & Drivetrain Systems 2 — Questions and Answers
Question 1: What is the primary purpose of a driveshaft center support bearing on a fire apparatus with a long wheelbase?
- To measure driveshaft rotational speed for ABS control
- To support and align a multi-piece driveshaft and reduce vibration (Correct answer)
- To lubricate the universal joints at regular intervals automatically
- To absorb torque spikes during transmission gear changes
Correct answer: To support and align a multi-piece driveshaft and reduce vibration
Center support bearings support long driveshafts at an intermediate point, preventing excessive flex and vibration that can damage U-joints and drivetrain components.
Question 2: A fire apparatus experiences severe driveline vibration that increases with vehicle speed. The MOST likely cause is:
- Low transmission fluid level
- Worn or out-of-phase universal joints (Correct answer)
- Excessive engine idle speed
- Incorrect tire inflation pressure
Correct answer: Worn or out-of-phase universal joints
Worn or incorrectly phased U-joints cause an imbalance in driveshaft rotation that produces vibration that intensifies as rotational speed increases.
Question 3: According to NFPA 1901, what is the minimum wheelbase requirement for aerial apparatus to ensure stability during outrigger deployment?
- NFPA 1901 does not specify a minimum wheelbase for aerials
- 120 inches minimum wheelbase
- NFPA requires a stability analysis rather than a fixed wheelbase (Correct answer)
- 96 inches minimum wheelbase
Correct answer: NFPA requires a stability analysis rather than a fixed wheelbase
NFPA 1901 requires manufacturers to conduct stability tests demonstrating the apparatus will not tip under specified loading conditions rather than mandating a fixed wheelbase dimension.
Question 4: What is the correct procedure for measuring the universal joint operating angle to prevent premature U-joint failure?
- Measure the angle at the output shaft flange only
- Use an inclinometer to measure the angle at both ends of each driveshaft section (Correct answer)
- Calculate the angle from the vehicle's published wheelbase specification
- Only measure U-joint angles when the vehicle is under full load
Correct answer: Use an inclinometer to measure the angle at both ends of each driveshaft section
An inclinometer placed at both the driving and driven ends of each driveshaft section allows calculation of the actual U-joint operating angle to verify it is within acceptable limits.
Question 5: Which component in an automatic transmission provides multiplication of engine torque during initial vehicle acceleration?
- Planetary gear set
- Torque converter (Correct answer)
- Valve body
- Output shaft
Correct answer: Torque converter
The torque converter uses fluid coupling between the pump (engine-driven) and turbine (transmission-driven) to multiply torque during startup and low-speed acceleration.
Question 6: A fire apparatus chassis has a tandem rear axle configuration. What is the PRIMARY advantage of this design for heavy apparatus?
- Improved fuel economy compared to single rear axle
- Increased payload capacity by distributing weight across more axles (Correct answer)
- Lower vehicle height for garage clearance
- Reduced tire wear on all axle positions
Correct answer: Increased payload capacity by distributing weight across more axles
Tandem rear axles distribute the vehicle's load across four rear tires instead of two, dramatically increasing total payload capacity while staying within axle weight ratings.
Question 7: When performing a pre-trip inspection on a fire apparatus chassis, which chassis lubrication point is most often neglected and can cause premature failure?
- Engine oil drain plug
- Fifth wheel plate (if equipped)
- Kingpin and steering knuckle grease fittings (Correct answer)
- Transmission fluid dipstick
Correct answer: Kingpin and steering knuckle grease fittings
Kingpin and steering knuckle grease fittings are frequently overlooked during routine maintenance but require regular lubrication to prevent wear and steering failure.
EVT Chassis & Drivetrain Systems 2
What is the primary purpose of a driveshaft center support bearing on a fire apparatus with a long wheelbase?