A truck’s differential is a crucial part of its drivetrain, and it shouldn’t be overlooked. Most differentials need a fluid change every 30,000 miles or so, particularly if the truck hauls heavy loads. The differential itself usually lasts around 200,000 miles.
Yet, a differential that’s taken damage, or one on its last legs, should be addressed as swiftly as possible. Differential dysfunction can be deadly, causing drivers to lose control of their heavy-duty vehicles while turning.
Learn the signs your differential is in trouble. Then, discover when it’s wisest to rebuild a differential, and when to replace it entirely.
Understanding Your Truck’s Differential (Overview)
A differential is a auto parts that distributes and directs energy from the engine to the wheels. It's attached to the axle. Its core purpose is to ensure the outer wheel rotates faster than the inner wheel during a turn. Essentially, the differential compensates for the difference in distances each wheel travels.
How Does a Truck’s Differential Work?
Differentials functionally split the torque energy from a single input (the engine) into two outputs. While designs vary, in general the outputs are pinions which rotate distinct components of the device.
According to the Universal Technical Institute, “The main components of the differential are the ring and pinion gears. The ring gear is attached to the carrier assembly, and inside the carrier is a set of smaller gears.
These smaller gears are often referred to as spider gears, which are made up of another set of pinion gears and the side gears. It is this set of gears that supplies the differential action. Following the power flow inside the differential, the pinion gear drives the ring gear, which rotates the carrier.
The carrier then drives the smaller pinion gears, which in turn drive the side gears. The drive axles are splined into the side gears, which then drive the wheels.”
As the carrier rotates distinctly from the pinion gears, the simultaneous rotations direct different degrees of rotational energy to the wheels, letting each wheel rotate at different speeds.
The “final drive ratio” refers to the gear ratio within the truck’s differential. The ratio indicates the multiplier used to calculate the number of teeth the ring gear has relative to the input piston.
Higher drive ratios can allow for faster acceleration, but they reduce fuel economy and limit the vehicle’s top speed.
Where Is The Differential Located?
The differential is located on the axle of a truck corresponding to the truck’s “drive.” The differential is positioned on the front axle in a front-wheel drive (FWD) vehicle, the rear axle on a rear-wheel drive vehicle (RWD), and both axles on a four-wheel drive vehicle (4WD).
Differential Parts & Components
Different types of heavy-duty truck differentials are comprised of different component parts. There are three overarching types of differential.
Open Differentials are the most basic type. They split torque, sending the most power to the wheel with the least traction. They're the most lightweight, affordable type of differential. But, when a wheel loses traction entirely (due to road conditions), the other wheel receives no power. This can cause both wheels to spin ineffectively. Thus, they're not ideal for trucks driving in all conditions.
In contrast, locked differentials (“lockers”) divert all available torque to the wheel with traction. They lock axles together, to make wheels rotate at the same speed.
Limited-Slip Differentials (LSD) are a balance of the two. An LSD enables the wheels to rotate at different speeds. But, if a wheel nears zero traction (i.e. starts to slip), the differential redirects more of the torque power to the wheel with more traction, to maintain forward movement.
Regardless of type, most differentials are gear assemblies utilizing these components:
- Large Gear
- Small Gear
- Gear housing
- Crown Wheel
- Pinion
- Propeller Shaft
- Rotating Cage
- Internal Half-Shaft
- Bearings
Warning Signs of Differential Dysfunction
Noise is often a sign of damaged or loose components that aren't interacting correctly. Whirring during deceleration is often a problem with pinion bearing position, while whining during acceleration indicates trouble with the ring or gears. Banging, clattering,or clunking every few feet are signs of broken gears or similarly serious damage.
Vibrations are the most common signs of the beginnings of a problem like component degradation.
Uneven tire wear is a sign the differential is no longer distributing torque effectively across all wheels.
Fluid leaks are a sign of a loose or damaged fluid line.
Other warning signs to look out for include: