Differentials and Axles
Differential operation, power dividers, differential locks, and axle types.
- Explain how a differential allows wheels to turn at different speeds
- Describe the function of power dividers and differential locks
- Identify different axle types including live, dead, tag, and pusher axles
Lesson 1
Differential Operation and Types
What a Differential Does
The differential allows wheels to turn at different speeds during turns. When a truck turns a corner, the outside wheel must travel a greater distance than the inside wheel. Without a differential, the inner wheel would scrub and skip, causing extreme tire wear and poor handling.
The differential uses a set of bevel gears (side gears and spider gears) mounted in a carrier assembly. The ring gear drives the carrier, and the spider gears allow the two axle shafts to rotate at different speeds while still transmitting torque to both wheels.
Gear Ratios
The differential gear ratio is determined by the number of teeth on the ring gear divided by the number on the pinion. A higher ratio (like 4.11:1) provides more torque multiplication for heavy loads and hills, while a lower ratio (like 3.42:1) provides better fuel economy at highway speeds.
Exam Tip
The differential allows wheels to turn at different speeds during turns. This is the core function - do not confuse it with torque multiplication (which is the ring-and-pinion gear ratio).
The differential allows wheels to turn at different speeds during turns by using spider gears to split torque while permitting speed differences. The gear ratio determines the balance between torque multiplication and highway efficiency.