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Ball Joints: How Much Play Is Too Much?
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By Counterman
While constant velocity (CV) joints are the most popular type of driveline joint in use today, universal or “U” joints are still in use on the driveshaft of many larger SUVs, trucks and vans. U-joints can handle a lot of torque, making them popular for these applications, but why did the CV joint rise in popularity? The question can be answered by looking at the operational aspects of a U-joint.
The basics are this: U-joints are located on the ends of a driveshaft, mounted between the driveshaft and a front and rear yoke. The front yoke attaches to the transmission and the rear yoke attaches to rear differential. As the engine moves from the effects of torque and as the suspension of a vehicle travels up and down, the angle of the driveshaft changes.
A U-joint does two things. First, it transfers the motion between the yoke(s) and driveshaft and, second, it does this at different angles, allowing for driveline movement. Here’s where the fun begins. When a yoke and the driveshaft are in perfect alignment, the velocity from one is transferred to the other at the same rate. However, when there is an angle between the two, the velocity of the driven member fluctuates continuously during rotation.
It can be hard to visualize, but the reason this happens is that as the angle of the U-joint changes, the two halves of the U-joint cross are forced to rotate on a different axis. The drive axis remains at a constant velocity, and the ends of the U-joint connected to it rotate in a consistent circular path at the same velocity.
The driven axis, however, rotates in a path which causes the distance of travel at the outer ends of the U-joint cross to increase or decrease in relation to the consistent points of the drive axis.
This effect results in the continuous fluctuation of velocity between the input and output sides of the U-joint. While the input remains at a consistent speed, the output speeds up and slows down as the points of the driven axis continuously alter between a long and short path of travel.
So, why don’t we feel that on a vehicle with a traditional driveshaft? Because there are two U-joints and the fluctuation on each end balances out, effectively allowing the driveshaft to provide a consistent output speed to the rear differential. The angle of the two joints must be the same, however, and it doesn’t take much wear in one for the angles to differ, and subsequently cause a vibration.
U-joints are known for their propensity to cause vibration, and an inherent disadvantage they have is the greater the angle of the U-joint, the greater the fluctuation in velocity. Anything over 30 degrees and the fluctuation dramatically increases.
The driveshaft I’ve described here represents the majority, but U-joints have also been used frequently in the past on the end of the front axles for a 4WD vehicle, and in the rear of independent rear suspension vehicles on the ends of short driveshafts, known as half-shafts. Have you ever noticed how jittery an old 4WD truck feels in the front when the hubs are locked, and you turn a corner? Now that you understand how the fluctuation in velocity of a U-joint changes as the angle increases, you know why.
You may have heard of a Double-Cardan U-joint. It is basically two joints side-by side with a common link-yoke in between. This is one of the original concepts for a true CV joint, and they are often referred to as this. The advantage they have is they offer smoother operation at greater angles, and they are common on 4WD trucks, and a common upgrade for lifted trucks where the driveshaft angle is altered considerably.
The drawback to a Double-Cardan joint is they are bulky, and they can still suffer from limitations due to operating angle. The operating limitations of a U-joint ultimately brought about the popularity of the modern CV joint, but the durability of U-joints means we’ll still be seeing them in certain applications.
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By Counterman
link hidden, please login to view, we took an in-depth look at the Consumer Price Index (CPI) and the average vehicle age, highlighting their significant roles in shaping the automotive aftermarket. At the time of publication, we hinted at further exploration into other critical factors that influence our industry, and today, I’ll fulfill that promise by examining gas prices and vehicle miles traveled (VMT), two indicators that give a snapshot of the economy and provide professionals a means to predict the future of the aftermarket landscape.
First, let’s look at everyone’s favorite expense: gas prices.
The fluctuations in gasoline prices in the United States are more than mere figures at the fuel pump; they serve as barometers for a variety of factors, including economic health, geopolitical tensions, consumer confidence and the vitality of the automotive aftermarket sector. Gasoline stands as a relatively inelastic commodity, with demand showing little sensitivity to price changes. This is largely because a significant portion of vehicle use, estimated at about 30% for commuting purposes alone, is essential and non-negotiable for many individuals, according to a University of Michigan study. When considering additional driving for school-related activities, errands and other purposes, visits to the gas station are an inevitable aspect of daily life.
This inelastic nature of gasoline consumption implies that rising fuel prices compress consumer spending power and escalate operational costs for businesses reliant on transportation. Consequently, there’s a logical link between fuel costs and mileage traveled, especially for discretionary travel. Recent studies, including research by AAA, reinforce this connection, suggesting that as gas prices climb, individuals adjust their travel and lifestyle accordingly.
AAA released an article in July 2022 summarizing the aforementioned research that they conducted. The article showed that 64% of U.S. adults made changes to their driving habits and/or lifestyle since March 2022, at a time when gas prices were hovering around $4.30 and peaking at $5.03 in June 2022, with 23% of consumers making major changes. As illustrated in the article, of the 64% who reported they were making changes in their driving and lifestyle, 88% said they would drive less, 74% said they would try to combine errands, 56% said they would reduce shopping or dining out, and 30% reported they will delay major purchases.
Putting these sentiments into the context of the automotive aftermarket, less driving will put fewer miles on vehicles, leading to extended periods in between the 3,000-5,000 mile oil changes, roughly 6,000-mile alignments and factory scheduled maintenance around the 30,0000-, 50,000-, and 90,000-mile marks. Additionally, if people have less disposable income, they may put off repairs or standard maintenance like an oil change, further increasing the interval of vehicle maintenance.
However, while less driving may lead to extended periods between routine maintenance tasks such as oil changes, alignments and factory scheduled services initially, this shift in consumer behavior presents a silver lining for the automotive aftermarket. With people potentially delaying maintenance due to reduced disposable income, it stands to reason, vehicles are likely to be held onto for longer periods. This not only increases the likelihood of maintenance and repairs in the long term, but also signals a decrease in the purchase of new vehicles. As a result, the market could see an uptick in older, used vehicles that require more frequent servicing and do not receive warranty services (in other words, an increase in the use of vehicles within the aftermarket sweet spot). This scenario underscores the importance of the automotive aftermarket in supporting vehicle longevity and reliability, highlighting a potentially robust market for service shops and parts suppliers alike.
However, despite the intuitive connections and survey research, some reports, such as one from TIME, paint a different picture. Research analyzing fuel prices and American driving habits from 2000 to 2022 indicates that by June 24, 2022, U.S. gasoline consumption was nearly 8.93 million barrels per day, slightly below the 9 million daily average since 2000, showing a minor 1% drop. Conversely, gas prices soared to 90% above their average for that period.
The results of the TIME analysis will be partially corroborated by some of the charts presented in this article, but it is important to understand that the data presented for miles driven is in millions, so even small spikes on a chart will represent rather larger scaled changes.
To begin our deep dive, we start with Chart 1, which sources data from the U.S. Energy Information Administration and reveals the trajectory of retail gasoline prices across several years, displaying a pattern of highs and lows that correspond with a multitude of external factors.
link hidden, please login to viewChart 1 As we observe the trend line from January 2014 to January 2024, we see a gradual increase with significant peaks and troughs. The trendline suggests a weak upward trend with considerable volatility, which can be attributed to a range of influences, from geopolitical events, supply disruptions, technological advancements and shifts in consumer behavior. While Chart 1 showing a decade of gas price fluctuations may not explicitly outline the impact on the automotive aftermarket as far as time is concerned (meaning that we can’t accurately predict the price of gas in a few years with time alone), the implications are significant. Higher gas prices can lead to increased demand for fuel-efficient aftermarket products or vehicles, as consumers look to optimize their vehicle’s performance.
Conversely, lower gas prices can result in more disposable income to pursue vehicle repairs or perhaps drive more in general, which will inevitably lead to a greater need for repairs and vehicle upkeep (more on that to come). Ultimately, whether gas prices rise or fall, the aftermarket can benefit from the resulting changes in consumer behavior, as vehicle owners seek to manage their operating costs or take advantage of economic conditions to use their vehicles more.
VMT: A Reflection of Changing Times
As previously stated, VMT can have a significant impact on the health of the automotive industry and the aftermarket. So, let’s jump into Chart 2, which showcases VMT data over the last 10 years, according to the Federal Reserve Economic Data (FRED).
This chart traces the VMT from January 2014 to October 2023, offering a graphical story of the nation’s driving habits.
link hidden, please login to viewChart 2 The data shows that simply counting on an increase in driving over time won’t work for predicting aftermarket service demand. Instead, aftermarket businesses should focus on the specific factors that influence driving habits, like economic trends such as inflation and cultural/societal trends such as remote work policies. This understanding is crucial for aftermarket businesses to effectively manage inventory, plan marketing and schedule services. Recognizing that vehicle use can vary widely, rather than following a steady climb, allows aftermarket companies to be more agile and meet their customers’ needs in real time.
Is There a Correlation Between Gas Prices and Vehicle Miles Driven?
Various reports and studies have highlighted a discernible link between gasoline prices and the distance traveled by drivers. However, a broader analysis of economic data reveals a more complex scenario. Despite the intuitive connection between fuel costs and driving behavior, the practical demands of daily life in America—such as commuting to work, school and other essential activities—often render the inclination to reduce driving due to higher gas prices moot. (See Chart 3 which integrates information from the preceding two charts.)
link hidden, please login to viewChart 3 While there’s a connection between gas prices and VMT, it’s relatively weak as indicated by the low correlation coefficient and the even smaller predictive regression score not presented, indicating the presence of other influential factors. For accurate market predictions, we must consider additional variables like geopolitical issues affecting oil supply, policy changes and shifts in oil demand, which can abruptly alter gas prices.
Similarly, VMT is influenced by factors such as public transportation availability, urban versus rural living patterns and societal shifts toward remote work or “walkable” cities. Changes in consumer preferences, such as a growing interest in environmentally friendly transportation options or online shopping, can also play a crucial role.
Therefore, automotive aftermarket professionals should consider integrating advanced analytics and diverse data sources into their decision-making processes. This could involve investing in resources that help analyze social, economic and political trends, alongside traditional market data. Engaging with experts in related fields, from energy economics to urban planning, can also enrich their strategic outlook. In summary, a proactive understanding of the diverse drivers behind market changes is essential to navigate the industry’s complexities, capitalize on opportunities and ensure lasting success in a constantly evolving market.
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By Counterman
What was wrong with universal joints anyhow? After all, they worked fine for years, and they still do! This is true, and U-joints can handle a lot of torque, but they do have a downside in the nature of their operating characteristics.
Here are the basics: U-joints are located on the ends of a driveshaft, mounted between the driveshaft and a front and rear yoke. The front yoke attaches to the transmission and the rear yoke attaches to the rear differential. As the engine moves from the effects of torque and as the suspension of a vehicle travels up and down, the angle of the driveshaft changes.
A U-joint does two things. First, it transfers the motion between the yoke(s) and driveshaft; and second, it does this at different angles, allowing for driveline movement. Here’s where the fun begins. When a yoke and the driveshaft are in perfect alignment, the velocity from one is transferred to the other at the same rate. However, when there’s an angle between the two, the velocity of the driven member fluctuates continuously during rotation.
It can be hard to visualize, but the reason this happens is that as the angle of the U-joint changes, the two halves of the U-joint cross are forced to rotate on a different axis. The drive axis remains at a constant velocity, and both ends of the U-joint cross rotate in the same consistent circular path.
The driven axis, however, rotates in a path that causes the distance of travel at the outer ends of the U-joint cross to increase or decrease in relation to the consistent points of the drive axis.
This effect results in the continuous fluctuation of velocity between the input and output sides. While the input remains at a consistent speed, the output speeds up and slows down as the points of the driven axis continuously alter between a long and short path of travel.
So, why don’t we feel that on a vehicle with a traditional driveshaft? Because there are two U-joints, and the fluctuation on each end balances out, effectively allowing the driveshaft to provide a consistent output speed to the rear differential. The angle of the two joints must be the same, however, and it doesn’t take much wear in one for the angles to differ, and subsequently cause a vibration.
U-joints are known for their propensity to cause vibration, and the other disadvantage they have is the greater the angle of the U-joint, the greater the fluctuation in velocity. Anything over 30 degrees and the fluctuation dramatically increases. Have you ever noticed how jittery an old four-wheel-drive truck feels in the front when the hubs are locked and you turn a corner? Now you know why.
You may have heard of a Double-Cardan U-joint. It’s basically two joints side-by-side with a common link-yoke in between. This is one of the original concepts for a true constant-velocity (CV) joint, and they’re often referred to as this. The advantage they have is they offer smoother operation at greater angles, and they’re common on four-wheel-drive trucks, and a common upgrade for lifted trucks where the driveshaft angle is altered considerably.
The drawback to a Double-Cardan joint is they’re bulky, and they still can suffer from limitations due to operating angle. True CV joints as we know them today have been around since the early 20th century, but the popularity of the front-wheel-drive (FWD) vehicle is what made them a household name.
Today’s CV joints are a radical departure from anything resembling a U-joint, and not only do CV joints transfer power without speed fluctuation, but they also can operate at angles up to and exceeding 50 degrees, depending on the joint. Since the drive wheels on a front-wheel-drive vehicle also steer, the ability for this increased operating angle is what makes the CV joint so beneficial for FWD.
A front-wheel-drive vehicle has two CV shafts – one on each side – and each shaft features an outboard and inboard joint. The outboard joints are considered fixed joints, meaning they don’t offer in and out movement. It’s their ability to operate at the increased angles for steering that’s important. The inboard joints are considered plunge joints, meaning they offer a wide range of inner and outer directional movement in order to make up for length differences as the suspension travels up and down.
Types of CV Joints
You’ll see two types of CV joints. One is the Rzeppa design, which features steel balls trapped in a cage and riding on an inner and outer race. The tri-pod design is the second, which features three roller bearings that ride in a race or cage, sometimes referred to as a tulip assembly. Both types of joints can be found in either a fixed or plunging design for outboard or inboard use, but the Rzeppa design has proven more popular as an outboard joint. The Rzeppa works well as an inboard joint too, but the tri-pod design gets the nod for the most effective operation as a plunge joint.
The CV shafts themselves can differ in length from side to side, and in early FWD development, torque steer – the vehicle pulling in one direction or the other during acceleration – was sometimes a result of this difference. Different diameter shafts as well as hollow versus solid became part of the design aspects to combat this problem. Drivetrain mounting and torque control have advanced considerably since the early days of FWD, and torque steer rarely is a problem.
Even though the FWD vehicle put the true CV joint on the map, due to their overall advantages, CV shafts now are utilized front and rear, and it’s not uncommon to see driveshafts that feature CV joints instead of U-joints. U-joints aren’t forgotten, however, due to their ability to handle high torque, and they work well in abusive environments that may not be so friendly to the boot on a CV joint (such as the exposed location of a driveshaft under a truck).
CV joints are packed with a specially formulated grease, and a rubber boot is sealed to both the CV shaft and the joint, to keep the grease in place. When a boot is torn or begins to leak, the grease goes away, and dirt gets inside. CV joints typically need no service until this happens.
There was a time when the most common service for a bad boot was to remove the CV joint, take it apart, clean it, repack it and install a new boot. Generally, this was routine. However, from time to time you could experience a nightmare. Much of the reason we replaced the boots and serviced the joints in this manner was due to the high cost of a replacement joint or a complete shaft. Even with the additional labor, it was far more cost-effective to replace just the boot.
Over time, with advancements in manufacturing and the availability of supplies, the cost of complete CV shafts went down, and it simply made more sense to replace them as a complete unit, not to mention it makes things easier for technicians.
Selling Tips
The most important part of selling a new CV shaft is making sure it’s the correct one. You should compare shaft length, the size of the CV joints themselves, and make sure it has an ABS tone ring installed if the vehicle is equipped with an anti-lock braking system. Some early CV joints had the tone ring cast into them, but that design was quickly abandoned for a press-fit tone ring. If your customer doesn’t yet have the original shaft out, be sure and make these recommendations to them so they ensure the shaft is correct prior to installation.
Installing a CV shaft is routine for professional technicians, but DIYers likely will have questions. One of the most important factors is torque of the fastener that secures the outer CV joint in the hub. If they don’t adhere to the factory procedure and don’t follow the correct torque specification, damage can and will occur to the wheel bearing.
Some CV-shaft applications come with an ABS tone ring installed, regardless of whether or not the vehicle is equipped with ABS. If not, in most cases, the ring has no consequence. However, in the rare situation where it rubs or contacts something, the rings can be removed easily.
The tricky part of CV-shaft service is there are some you can have out in a few minutes without even removing a wheel, and others that may take an hour or longer. The majority of them require some portion of the suspension to be separated, so the outer joint can be pulled out of the wheel bearing, then the entire shaft pulled outward as it’s removed from the transaxle. It’s fair warning that this is not always easy and might require specialized tools. As long as you convey that to the customer, they can’t say you didn’t warn them.
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By Yu Billy
link hidden, please login to view Name：Steering gear/without ball head
OE Number： link hidden, please login to view/7D1422061BX
Product Line: TR models
Product brand:Vika
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By OReilly Auto Parts
The ball joints on your vehicle are structural components that allow the suspension to move at different angles for steering and ...
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