Chassis & Drivetrain Systems Flashcards
7 cards from real EVT practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Chassis & Drivetrain Systems flashcards as text
What does the term 'axle ratio' refer to in a fire apparatus drivetrain?
Answer: The number of driveshaft rotations per one axle rotation
Axle ratio (also called final drive ratio) is the number of times the driveshaft (pinion) rotates for every single rotation of the axle (ring gear), affecting torque multiplication and top speed.
A technician notices excessive play in the steering wheel of a fire apparatus before the front wheels begin to turn. This symptom is MOST likely caused by:
Answer: Worn steering gear, ball joints, or tie rod ends
Excessive steering wheel free play (lash) is typically caused by worn components in the steering linkage such as the steering gear, ball joints, or tie rod ends that allow movement without transmitting it to the wheels.
NFPA 1901 specifies that the manufacturer must provide a document showing what information about the chassis for each new fire apparatus delivered?
Answer: Gross vehicle weight rating, front and rear axle ratings, and payload capacity
NFPA 1901 requires the manufacturer to provide documentation of the GVWR and individual axle weight ratings so the authority having jurisdiction can verify the chassis is properly rated for the loaded vehicle.
What is the purpose of the inter-axle differential (power divider) on a tandem-axle fire apparatus?
Answer: To allow the two rear axles to rotate at different speeds when turning without binding
The inter-axle differential (or power divider) allows the two tandem drive axles to rotate at different speeds when the vehicle turns, preventing driveline binding while still distributing torque to both axles.
Which condition would cause a fire apparatus automatic transmission to slip out of gear or hunt between gears during operation?
Answer: Low or contaminated transmission fluid
Low fluid level reduces hydraulic pressure needed to engage clutch packs, while contaminated fluid can clog valves in the valve body, both causing erratic shifting or gear hunting.
When replacing a driveshaft on a fire apparatus, what MUST be marked before disassembly to ensure correct reassembly?
Answer: The phasing relationship and orientation marks of all yokes and slip joints
Yoke phasing and orientation marks must be transferred before disassembly so the driveshaft is reassembled with correct U-joint phasing, preventing vibration and premature component failure.
A fire apparatus technician is checking the front axle caster angle. What handling characteristic does insufficient positive caster primarily affect?
Answer: Straight-line stability and steering returnability
Positive caster creates a self-centering effect that helps the steering return to straight after a turn and improves directional stability; insufficient caster causes wandering and poor returnability.