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:
- Overheating
- Rapid oil consumption
- Steering control problems
- Trouble shifting gears
- Grinding gears
- Metal shavings in oil
- Trailer sway
The severity of the damage, your truck’s mileage, and limits on your budget and time determine whether your differential needs to be rebuilt or replaced.
Converting your differential from one type to another can be done via rebuild or replacement.
When To Rebuild Your Truck’s Differential
If you're experiencing any of the warning signs described in the previous section, it may be time to rebuild your differential. Rebuilding a differential means repairing or replacing components in the differential’s housing, but leaving the casing and most of its undamaged parts.
Rebuilding a differential can change its final drive ratio. Thus, it can be an effective option to improve your truck's performance as well as address signs of damage.
Rebuilding Is Ideal When Damage Is Minor
Rebuilding can involve a range of repair and modification tasks to improve the differential. These can include:
- Seal leaks by repairing or replacing gaskets and seals
- Flush and change out fluid
- Replace deteriorating bearings
- Repair chipped gears
- Realign or reposition components
- Secure loose components
- Install components (clutch packs, friction discs, etc) in existing housing to transform open differential to LSD
Rebuilding is a better option than a full differential replacement if your truck has low mileage and only minor components have taken damage.
Benefits of a Differential Rebuild
Differential rebuilds offer a few advantages over replacements.
- Rebuilds can be completed faster
- Rebuilds are less expensive than replacements
- Rebuilds solve minor differential problems swiftly
- Rebuilds let you get back on the road safely
- Rebuilds have a lower environmental impact than replacements
When To Replace Your Truck’s Differential
The symptoms listed in the Warning Signs section can indicate minor or major problems. Your truck's differential may need to be replaced entirely if, upon assessment, you discover serious damage to the housing (casing) of the gear assembly, the input piston, or the majority of components.
Replacement Is Best For Major Damage To Gears, Housing or Bearings
Replacing the differential is necessary when the gear casing is damaged. Other issues, like gear grinding combined with poor steering control and fuel inefficiency, often point to replacement being the best choice. Replacing a differential often involves:
- Sourcing or fabricating large replacement parts, or an entirely new model
- Installing the new differential
- Upgrading to a better differential
Replacement is a better option than rebuilding if your truck has high mileage and gear housing has taken damage.
Benefits of Replacing Your Truck’s Differential
Replacing your truck’s differential can solve key safety and handling issues, improve fuel efficiency and driveability, and upgrade your differential to the model best-suited to your truck.
Differential Assessment: Rebuild Vs. Replace
There are several factors to consider when choosing whether to rebuild or replace your truck’s differential. These include:
- Sourcing expenses and labor cost to replace rear differential
- Differential rebuild cost, including installation time and skill
- Your truck's mileage (lower mileage trucks see greater benefit from rebuilds)
- The severity of damage to the differential
- Whether or not the gear housing was damaged
- Whether you're still within your differential’s warranty period
- The truck’s typical use
Cost Comparison
It's challenging to compare the cost of rebuilding a differential and replacing it.
Rebuilds can be time intensive, which raises labor costs. But, an entirely new differential costs more outright than individual components cost—unless those components are challenging to source or fabricating.
Moreover, a differential under warranty may cost you little to nothing to replace, as the warranty will pay for it.
While there's considerable variation, rebuilds generally cost between $800 - $1500, while replacements start at $1500 and can climb upwards of $3500.
Prevent Differential Failure With Regular Maintenance
Be sure to change out your differential fluid every 30,000 miles. Check your truck's owner’s manual to determine which high-quality gear oil is appropriate for your model.
Engage in regular inspections, specifically looking for signs of leaks, metal shavings, or degraded components. It's easy to integrate a leak check into your oil change routine.
Know your truck's weight limit, and never overload its axles beyond those specifications. Address signs like vibrations and noises as soon as you observe them.
Get Excellent Differential Rebuilds or Replacements Fast
At Point Spring & Driveshaft Co, our pros work with you to get your commercial vehicle the right service—whether that's a simple differential fluid change, a partial ebuild, or a complete replacement and upgrade.
If you're interested in differential services, call +1 (412) 264-6714. Or, bring your heavy-duty truck to any of our locations listed below.