Axle Assembly Buyer's Guide
- Most vehicles rely on an axle assembly to transmit torque from the transmission to the wheels. Problems in this system will hamper or even stop your car’s movement.
- Depending on a vehicle’s engine and transmission layout, it can have either a front axle assembly, a rear axle assembly, or both.
- Axles can be classified based on their structural features and drive.
- Some of the symptoms of a bad axle shaft or worn-out axle assembly include clicking noises while accelerating or making turns, grease leaking onto the tires, and palpable vibrations.
- When getting a new axle assembly, identify the vehicle's load-bearing end, since the axle assembly of this half will experience more wear and tear.
- When buying rear axle assemblies, select one made from high-grade steel with many splines. For front axle assemblies with both outer and inner splines, get parts with strong CV joints.
- A new axle assembly can cost anywhere between $27 and $9,433 on CarParts.com.
Most vehicles rely on an axle assembly to transmit torque from the transmission to the wheels. Problems in this system will hamper or even stop your car’s movement, so it helps to know the warning signs of a bad or failing system, as well as what qualities to look for in a potential replacement part.
What is the axle assembly?
The axle assembly gets its name from the axle shafts that comprise the system. Each shaft is a thin cylinder that physically connects the wheels and the transmission gears.
Torque from the transmission travels through the axle shafts and into the wheels attached to the shafts. The rotational force spins the wheel, which moves the car over a road surface.
A working axle assembly makes it possible for a vehicle to run, speed up, slow down, and make turns without a hitch. However, if an axle shaft wears out or malfunctions, you will find it more difficult to operate your car.
Front axle assembly or rear axle assembly?
Depending on a vehicle’s engine and transmission layout, it can have either a front axle assembly, a rear axle assembly, or both.
Front-wheel-drive vehicles have driven front axle assemblies while rear-wheel drive systems power the rear axles. All-wheel-drive vehicles, on the other hand, combine both types to power all four wheels for maximum power and traction.
Types of car axles
The axle assembly is the drive train part that takes the gross weight of your vehicle, together with its cargos, while bearing all the forces in your auto as you accelerate and brake. There are different types of axles according to structural features. The straight one is used in trains and in the rear axle assembly of heavy-duty vehicles. Meanwhile, the split-axle is used in passenger vehicles while the tandem axle is perfect for autos carrying greater weight.
Axles can also be classified according to their drive. Front-wheel driven vehicles have transaxles, the combination of transmission and the front axle assembly. Rear-wheel driven ones, on the other hand, have a live axle. This axle receives rotational force from a driveshaft driven by the engine. There are also those considered dead or lazy axles, not parts of the drivetrain but are instead freely rotating.
Symptoms of a bad or failing axle assembly
Fixing or replacing a car axle shaft can cost a pretty penny while changing out the entire assembly will cost even more. You should make sure that the problem comes from the axle assembly.
Some of the symptoms of a bad axle shaft or worn-out axle assembly include:
When you accelerate your car or make a turn, you may hear clicking noises coming from the axle assembly. The noises come from the metal parts of an axle shaft when they touch or hit each other.
In a working axle assembly, those parts shouldn’t touch thanks to lubrication and design. However, worn-out surfaces or loss of lubricants can increase the contact.
On the upside, the clicking noise made by the faulty axle assembly can help you localize where the problem lies. Listen carefully to find out if it comes from the front end or the rear half of your vehicle.
The boots not only encase joints between the transmission, axle assembly, and wheels, but they also hold the lubricants that reduce friction between the moving metal parts.
A damaged or degraded boot will leak grease into the wheel connected to the component. The leaking lubricant can warn you about a problem with the axle assembly.
Inspect your tires for any signs of grease that do not belong there. Take a good look at the inner edges where the lubricant likely collects.
A broken inner joint in the axle shaft causes more vibrations because the part no longer fits tightly. You will feel the increased shaking whenever you hit the accelerator and speed up the vehicle.
However, unrelated mechanical issues can also cause the axle assembly to vibrate. Before buying a replacement axle shaft or axle assembly, make sure the problem doesn’t stem from those parts.
Picking a new axle assembly
Some drivers need a replacement for an old, damaged, or broken axle assembly. Others want to upgrade the axle shafts of their pickup truck or SUV because they plan to travel long distances, go off-roading, or haul heavy loads with their vehicles.
Whatever the reason for getting a new axle assembly, it helps to keep several things in mind.
Identify the vehicle’s load-bearing end
Determine which end of the vehicle bears most of its weight when heavily or fully loaded. The axle assembly of the load-bearing end suffers more wear and tear, making it much likelier to need repair or replacement.
The rear halves of most vehicles contain either the trunk or cargo bed. Since the cargo-carrying half hauls heavier loads, the rear axle assembly tends to wear out faster or need reinforcement.
Pick a steel rear axle assembly
A rear axle assembly must use the strongest materials that can withstand the stress from transmitting torque and the heat produced by its operation. Always pick an assembly made from high-grade steel.
Splines on the axle shafts of the rear axle assembly
The end of an axle shaft features splines that fit into the grooves of the hub and shaft of a wheel. These rectangular-shaped keys lock the shaft in place within the wheel so that the two parts turn together upon the application of torque from the transmission.
The more splines on the axle shaft’s end, the greater the strength of the axle assembly. Given a choice between a 28-spline axle and a 40-spline axle, the latter proves stronger.
CV joints of the front axle assembly
For structural strength, the front axle assembly relies on its constant velocity (CV) joints. Each joint consists of an axle and a small volume of steel, and they connect the axle shafts to the transmission.
Torque from the transmission passes through the CV joint. Smaller than the axle shaft, the joint must withstand the full power of the engine.
Outer and inner splines
Furthermore, the axle assembly of most front-wheel drive vehicles uses both outer and inner splines. While the outer spline slots into the wheel hub, their inner counterparts fit together in the differential. Similar to the rear axle assembly, more splines translate to stronger axle shafts.
Things to consider when buying an axle assembly
- When buying a rear assembly, make sure you buy one that's made of steel. This type of axle assembly is made to be very strong.
- The strength of the rear axle assembly depends on the number of splines that are machined at the end of the axle. Always remember that "the greater the number of splines, the stronger the axle assembly". For increased performance, a 40-spline axle is stronger than the 28-spline.
- When buying a front axle assembly, take note that the strength depends on the power of the CV joint. In this situation, the force of the engine does not pass through solid steel axle assembly, but instead through a very small area of steel and a bearing.
- The usual design of front-wheel drive axle assembly uses both an outer and inner splined area. The outer spline fits into the wheel hub, whereas the inner spline fits together in the differential.
These are just some basic things to keep in mind whether to purchase the front or the rear axle assembly. Good luck!
Cost of a replacement axle assembly
A new axle assembly can cost anywhere between $27 and $9,433 on CarParts.com. Available in single pieces, sets of 2, and as part of a replacement kit, they can replace broken OE assemblies or offer improved performance over factory-issue axle parts.
It can prove expensive to replace axle shafts, much more the axle assembly. You can save yourself trouble and expenses by getting car axle parts guaranteed to fit your vehicle. Enter your vehicle’s year, make, and model in CarParts.com’s filter bar to narrow down the available choices.
Assembling the axle assembly
If you start hearing clicking noises when you turn the car or feel the vehicle vibrating only when it accelerates, chances are that your axle assembly is worn out. Probably, there's a torn boot with grease that's slinging out or the vibrating upon stepping on the accelerator indicates a broken inner joint. Whatever the case is, you have to repair the axle assembly. But don't worry because we're here to help you out.
Difficulty level: Moderate
- Mallet hammer
- Ball joint separator
- Torque wrench
Reminder: Make sure that you wear safety goggles when working. Also, wear gloves and closed toe shoes to avoid any injury.
Step 1: Park your car on a flat surface. Set the parking brake and block the rear wheels.
Step 2: Loosen up the front wheel lug nuts but be careful not to remove them. Using the floor jack, lift up the front of the vehicle.
Step 3: Take the jack stands and slide it under the car to support it. Before working, make sure to have each on both sides for safety. The best locations for these are the frame rails and the pinch welds. However, don't solely rely on the jack to hold up the vehicle in the whole duration of the process.
Step 4: Take out the lug nuts and remove the front wheels and set them aside.
Step 5: Check the CV boots and joints if they are damaged.
Step 6: Remove the axle nut from the busted axle assembly. Support the lower control arm with the floor jack. Separate the tie rod end and the lower ball joint from the steering knuckle. To take out the knuckle from the assembly, push the axle in and lift the steering knuckle up and out. Make sure to support it with a wire.
Step 7: Pull out the axle assembly from the differential or transaxle. If needed, hit the axle assembly using a rubber mallet. Then, insert the new axle assembly into the transaxle.
Step 8: Install the outer joint of the assembly into the steering hub/knuckle assembly. Reattach the lower ball joint and tie rod end to the steering knuckle. Install the axle nut.
Step 9: Put the front wheels back and tighten the lug nuts. Remove the jack stands and lower down the car.
Step 10: Torque the axle nut and the wheel lug nuts in a star pattern, according to the specifications of the manufacturer. Test the car and you're done!