Arguably the most important part of your driveline’s performance are the tires and wheels that help deliver a car’s power to the ground for safe movement. The driven wheels on any vehicle are connected to the differential or transaxle, which means that these wheels can rotate at different speeds when making turns. This is because one wheel needs to travel a slightly longer distance to make the turn at the same speed as its adjacent wheel without binding or other driveability issues. There are a variety of wheel- and tire-related factors that can affect a vehicle’s comfort and responsiveness. A centered, balanced, stable tire and wheel assembly is needed to allow the vehicle to travel, and proper tire tread depth and tire condition is required for traction that allows you to more easily and safely move a car. This means that any malfunction, wear, underinflation, or imbalance of the wheels and tires can create noticeable issues.
While some cars look nice even when they’re parked, having to park your car to make repairs is never enjoyable — that’s why understanding your car’s driveline can help you more quickly and easily identify any potential issues to keep you safe and on the road. Just as the name states, the driveline of your vehicle is designed to transfer engine power through the transmission to the wheels to keep your car moving. A poorly aligned or damaged driveline can cause your vehicle to not move, or move with excessive effort, which can affect your ability to drive safely or enjoyably. Below, we will explore the symptoms of a bad driveline, and how to easily diagnose specific components that can help you repair driveline components to keep your car performing as it should.
What’s The Difference Between A Driveline, Drivetrain, and Powertrain?
When discussing power distribution on a vehicle, the terms ‘driveline’, ‘drivetrain’, and ‘powertrain’ are used often, and properly defining the differences between these words can help you understand your car better. Although some use the three terms interchangeably, there are differences between a powertrain, driveline, and drivetrain.
- The term 'powertrain' describes all of the parts and systems that provide power to a vehicle, including the engine, transmission, and driveline.
- The word ‘drivetrain’ is also often used when discussing the powertrain, but does not include the engine — this means that a drivetrain is referencing the transmission and driveline components specifically.
- Finally, ‘driveline’ describes the drivetrain, but without the transmission. Driveline components (which we will cover in-depth below) include the wheels, hubs, wheel bearings, axle shafts, U-joints, CV shafts, the driveshaft, and differential(s).
These systems may sound overwhelming if you aren’t familiar with their design or operation, but all three terms exist to help discern the source and transmission of the power that helps the vehicle move, and can help clarify the systems being discussed to increase automotive knowledge.
Why Do Drivelines Fail?
Like most of a vehicle’s electronic and mechanical components, heat exposure, constant use, and stress due to more severe use can cause parts of your driveline to fail over time. There are a variety of parts in a car’s driveline that help transfer power, and each of these components can sustain wear due to corrosion, misalignment, or damage from towing and other demanding tasks. Understanding the purpose and design of each part of your driveline can help you better narrow down and diagnose the potential source of your vehicle’s power distribution issues.
What Does A Driveline Do?
As described above, the purpose of a driveline is to transfer the engine’s power to the wheels smoothly to keep your vehicle moving. In its simplest terms, a driveline is the drivetrain after power leaves the transmission. A common driveline consists of constant velocity (CV) axles, also called CV shafts and/or driveshaft(s), U-joints, hub assemblies, wheels, center support bearings, and differentials which may include axle shafts. Each part of the driveline has a specific function when helping the vehicle move, and understanding the warning or failure signs of each component can help you better identify starting points for your inspection. Below we will outline the parts of a driveline to help you better recognize the signs of a bad driveline or driveline components to prevent an untimely roadside emergency and restore your car’s performance and handling.
Wheels & Tires
Signs Of Improperly Inflated Tires Include:
- Increased or uneven tire wear
- Reduced fuel efficiency
- Shorter tire lifespan
- Skidding
- Diminished handling
Want more information about tire inspection and health? Our tire pressure tips article describes how different levels of tire pressure can affect your vehicle. If you’d like to know more about your tires and the importance of tire pressure, visit our How-To Hub for information like how to check tire tread and when to replace a tire, how to rotate tires, how to check tire pressure, and much more.
Another variable that could cause your wheels to underperform is a bent wheel rim. Whether it’s caused by hitting a curb, driving with a flat tire, or being involved in an accident, the metal wheel rim can become dented, damaged, or bent. This can cause noticeable changes in the way your vehicle drives and result in wobbling, poor balance, and accelerated wear of tires and other parts. Any type of structural damage to your wheels can severely impact or damage the steering system, wheels, and tires of the vehicle, and should be addressed as soon as possible. O’Reilly Auto Parts has valve stems and tools, wheel cleaners, tire pressure gauges, and many more tire and wheel parts to help you repair or maintain your ride’s rims.
Signs Of A Bent or Damaged Rim Include:
- Diminished handling
- Vibrations or an excessively bumpy ride
- Increased tire wear
One last consideration when inspecting your wheels is the overall balance of the wheel and tire assembly. To make sure that each tire rotates smoothly and evenly, wheel weights are used to balance each wheel to prevent vibrations, offer better tire performance, and deliver a smoother ride. Wheel weights can be found in clip-on and adhesive varieties, and are attached to your wheel’s rim with the help of a tire balancing machine for exact counterbalancing. While balanced wheels rotate more evenly, unbalanced wheels can put added stress on the wheel bearings, shocks, and hub assemblies. Your vehicle likely already has wheel weights installed, but if it is in need of rebalancing or needs replacement wheel weights after a collision or when you change your tires, it may be necessary to take it to a tire shop for accurate balancing. When replacing or installing clip-on wheel weights, it’s important to match the weight’s design and shape with the shape of the rim flange. Improperly-installed wheel weights may fall off or scratch the rims, and this will leave your vehicle’s wheels improperly balanced. You should always have any broken or missing wheel weights replaced before they begin to impact your vehicle’s drivability. If you notice the signs of an out-of-balance wheel that are listed below, consider having your wheels balanced professionally to restore your car’s comfort and safety.
Signs Of Unbalanced Wheels Include:
- Uneven, rapid tire wear
- Vibrations that increase with speed
- Shaking that seems to be coming from one specific area of the vehicle
- Vibrations felt in the steering wheel, floors, or seats
- Decreased gas mileage
You can find the tire and wheel tools for your DIY tire repair and maintenance at O’Reilly Auto Parts to help keep you driving safely. We carry everything you might need, from basic maintenance parts and tools to puncture repair kits and more. If you’re not comfortable performing a tire or wheel repair yourself, we can help you find automotive shops near you for a better performing vehicle and trusted service.
Differentials
The differential is one of the most complex parts of the vehicle’s driveline. The differential in your vehicle allows for smooth power delivery, and is found in all vehicles in some capacity. All-wheel, rear-wheel, and four-wheel drive vehicles may have a differential installed in an axle assembly, or they could have a differential connected to hub assemblies using CV shafts. Front-wheel drive vehicles typically employ a transaxle, which is a combined transmission and differential that typically uses CV shafts to transfer power to the wheels. Every vehicle has a specific type of differential design based on their build and related performance demands. Most vehicles that do not include a transaxle have a front and/or rear differential. The differential receives power through the pinion shaft and gear, which turns the ring gear and carrier gears that help transfer power to the wheels while also allowing them to move at different speeds during turns.
A failing or unbalanced differential, or a vehicle under stress due to severe performance demands or heavy loads, can contribute to its eventual wear or failure. The gears of the differential may suffer damage due to a lack of lubrication or with extreme use, and this can allow the differential to slip or make noise. O’Reilly Auto Parts has the differential parts you need for your repair, including differential gears, differential carriers, rebuild kits, and much more. Want more information on how to maintain your differential? Visit our How-To Hub for helpful topics like how to change rear differential fluid and more to help you stay on top of your vehicle’s driveline maintenance.
Signs Of A Bad Differential Include:
- Sounds from axle assembly at the front or rear of the vehicle
- Vibrations that change intensity with speed
- Axle hop while steering
- Howling or grinding sounds caused by worn gears
- Obvious tire wear
Hub Assemblies & Wheel Bearings
The hub assemblies on a vehicle are a critical component to keeping your wheels in contact with the road. A ‘hub assembly’ describes a rotating assembly that includes a hub as well as wheel bearings that allow the entire assembly, and thus your wheels, to spin. In some vehicles, the hub assemblies and bearings may also be linked to the anti-lock braking system (ABS) or vehicle speed sensor (VSS), and feed that information to the engine control unit (ECU) or ABS module to indicate hard braking or a loss of traction. The car’s hub assemblies and wheel bearings are in motion any time the vehicle is moving, and due to constant use, stress, and heat, these components can wear out over time.
Signs Of A Bad Wheel Hub Assembly Or Wheel Bearings Include:
- Vibration felt in steering wheel when turning
- Popping sound heard at the wheel ends
- Uneven tire wear
- Diminished steering control and handling
- Roaring or clicking noises heard when driving
Driveshafts
Sometimes called a propeller or prop shaft, a driveshaft is the first step in transferring power from your transmission to the differential and axles. Found in many trucks, SUVs, sedans, and other rear-, all-, and four-wheel drive vehicles on the road today, a driveshaft is a long cylinder that includes U-joints at each end and transfers torque and power across a long distance to reach the differential and turn the wheels. The driveshaft itself rarely fails, but it can be damaged due to impact or if it falls out of balance. This can cause vibrations and accelerate wear to the U-joint, transmission, or differential. It is much more common that the U-joints which connect the driveshaft to the transmission yoke and the pinion shaft of the differential will eventually wear out due to a lack of lubrication or age and require service or replacement.
Signs Of A Bad Driveshaft:
- Vibrations or shuddering felt during deceleration, acceleration, or while under a load
- Scraping or rattling noises heard when driving
- Visible damage, denting, or excessive corrosion
U-Joints
A vehicle’s universal joints, also called U-joints, help connect the transmission and driveshaft to continue to carry power at the articulating points of the driveshaft as its angle changes due to suspension movement. Commonly found in all-wheel, four-wheel, and rear-wheel drive cars and trucks, the U-joints in your car include a number of small needle bearings below a sealed cap, making them susceptible to damage and wear due to friction if the U-joint is not lubricated. A failed U-joint can cause significant damage to your vehicle, as a broken U-joint can cause your driveshaft assembly to become loose and possibly even separate from your car. This can damage the driveshaft or parts of the undercarriage and leave you stranded.
Signs of Bad U-Joints Include:
- Clunking sounds or vibrations when accelerating or decelerating
- Looseness in the driveshaft which can cause balance issues
- Knocking noises when shifting gears or when taking off from a stop
CV Joints & CV Axles
Constant-velocity (CV) joints are a part of the driveline that helps connect your wheels to the transaxle or differential. CV shafts are found in some all-wheel drive and four-wheel drive vehicles, as well as most front-wheel drive cars, to deliver power to the hubs. CV axle shafts in your vehicle receive power from the differential or transaxle to drive the wheels, and include CV joints at both ends to allow them to articulate during steering or suspension movement. This allows power to continue to be delivered to the wheel, even at a variety of angles. The rubber boots of an axle shaft prevent grease from leaking to keep the CV joints properly lubricated. Over time or due to a damaged CV boot, road debris, moisture, or other grease contamination can occur which may cause corrosion or damage and prevent the CV shaft from moving as it should.
Signs Of A Bad CV Joint or CV Axle Shaft Include:
- Clicking or popping noises when turning
- Diminished handling
- Vehicle shaking sideways during acceleration
- Vibrations felt at high speeds
- Grease leaking from or damage to CV boot
It’s best to fix an issue when it arises rather than waiting until you’re on the side of the road — especially when it comes to your driveline. A bad U-joint, failing differential, or off-balance driveshaft or CV shaft can leave you stranded, but knowing the warning signs of bad driveline components can help you repair and replace the right parts the first time. O’Reilly Auto Parts carries CV joint kits, U-joints, grease, and many more CV axle and driveshaft parts online and in-store. You can also find helpful advice in the O’Reilly How-To Hub, with topics to help you repair, maintain, and service your vehicle to stay on the road safely.