EVT Chassis & Drivetrain Systems 3

Question 1

What does the term 'axle ratio' refer to in a fire apparatus drivetrain?

Accepted Answer

The number of driveshaft rotations per one axle rotation

Answer

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.

Question 2

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:

Accepted Answer

Worn steering gear, ball joints, or tie rod ends

Answer

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.

Question 3

NFPA 1901 specifies that the manufacturer must provide a document showing what information about the chassis for each new fire apparatus delivered?

Accepted Answer

Gross vehicle weight rating, front and rear axle ratings, and payload capacity

Answer

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.

Question 4

What is the purpose of the inter-axle differential (power divider) on a tandem-axle fire apparatus?

Accepted Answer

To allow the two rear axles to rotate at different speeds when turning without binding

Answer

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.

Question 5

Which condition would cause a fire apparatus automatic transmission to slip out of gear or hunt between gears during operation?

Accepted Answer

Low or contaminated transmission fluid

Answer

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.

EVT - Certified Emergency Vehicle Technician Practice Test

EVT - Certified Emergency Vehicle Technician Practice Test

EVT Chassis & Drivetrain Systems 3