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By Counterman
A constant velocity (CV) axle includes the axle shaft itself, along with the inner and outer CV joints as an assembly. The shaft itself is a rather mundane part, although there is more to them than meets the eye, but I’ll get to that in a little bit.
Perhaps the most interesting part about a CV axle is the joints, but it all seems more significant when we first look into their predecessor, the infamous u-joint. U-joints can handle a lot of torque, but they have a downside in the nature of their operating characteristics.
The basics are this: u-joints are located on the ends of a driveshaft, the most typical configuration a rear-wheel-drive vehicle, in which the joints are connected to 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.
U-joints transfer the motion between the yoke(s) and driveshaft at different angles, allowing for driveline movement. 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 both ends of the u-joint cross rotate in the same consistent
circular path.
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. 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.
A Double-Cardan u-joint. It is basically two u-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 are often referred to as this. The advantage they have is they offer smoother operation at greater angles, and they are common on four-wheel-drive trucks, and also 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. 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 FWD vehicle also steer, the ability for this increased operating angle is what makes the CV joint so beneficial for FWD.
A FWD 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 take up for length differences as the suspension travels up and down.
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.
link hidden, please login to viewTypical Rzeppa CV joint design. The CV shafts themselves can differ in length from side to side, and in early FWD development, torque steer, the vehicle pulling 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 has also advanced considerably since the early days of FWD, and torque steer is rarely a problem.
Due to their overall advantages, CV shafts are now 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 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).
link hidden, please login to viewTypical U-joint. 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.
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, and if the vehicle is equipped with antilock brakes with a tone ring on the outer CV joint, be sure the replacement has this ring. 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, recommend they make these comparisons prior to installing the
new shaft.
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 final, and perhaps most important, recommendation is to always torque the fastener that secures the outer CV joint in the wheel hub. If the factory procedure is not adhered to and the correct torque specification not used, damage can and will occur to the wheel bearing. CM
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By Counterman
Stabilizer bars. You may know them as sway bars or anti-sway bars. You may know them as roll bars or anti-roll bars. They’re all the same thing, and it’s generally understood they improve handling … but how?
Any time a vehicle is turning, the forces that act upon it cause the body to roll, sway or tip away from the turn. It’s the laws of physics at work. In extreme situations, these forces can cause a vehicle to tip over, though that’s generally only the case with taller trucks and vans, and rare at that. You really have to be moving for that to occur. The real factor is how they negatively affect handling and how a stabilizer bar can prevent it from happening.
Picturing this “tipping” affect helps us understand how a stabilizer bar works. When driving in a straight line, the weight of the vehicle is evenly distributed between left and right. In a turn, as the vehicle body leans, it shifts the weight to the tires on the outside of the turn, compressing the suspension on the outside in the process. This shift in weight causes a loss of traction on the inside, resulting in poor handling and potentially the loss of control.
A stabilizer bar connects one side of the suspension to the other. They can be located in the front, rear or both. They’re mounted to the frame or body with brackets and bushings, and connect to the suspension at the control arms or struts. The connection at the suspension can be a bracket and bushing or a link, which is the most common today.
When any suspension movement occurs, that movement is transferred into the stabilizer bar, which then is transferred through it to the suspension on the other side. This balances the compression of the suspension on both sides, eliminating body roll, balancing the weight distribution of the vehicle and providing optimum traction and handling.
You’ve likely heard the terms oversteer and understeer. Understanding and controlling them is one of the most important aspects of performance driving, and it’s an important aspect of new-car design. They’re relevant in this context because both are affected directly by the action of the stabilizer bar.
For this reason, adding or changing stabilizer bars is a common practice for those who look to improve the handling performance of their car. If you increase the stiffness of the rear stabilizer bar or decrease the stiffness of the front, you reduce understeer. If you increase the stiffness of the front stabilizer bar or decrease the stiffness of the rear, you reduce oversteer. Someone who is building their car for performance or racing will spend hours on stabilizer-bar adjustments alone until they “tune” the handling of their car.
For many years, sway bars were just an option, or only located in the front. But due to the improvement in handling they provide, most of today’s cars and trucks have them.
Stabilizer bars are just a piece of metal. Some are a solid bar, some are hollow. Each one offers different performance aspects in how much they twist versus how much force it can transfer to the other side of the suspension. In addition, performance stabilizer bars and/or their connecting links often are adjustable at each end to provide an additional range of tuning.
One drawback associated with stabilizer bars is they can affect the overall ride quality of a vehicle. The stiffer the sway bar, the better a vehicle may handle – but the worse it will ride. In trucks and SUVs, the sway bar limits suspension travel, which is a drawback to those who use them for off-roading.
Leave it up to technology to take it one step further with active and electronically disconnecting stabilizer bars. Active stabilizer bars are found on some luxury performance cars. They work by using an electric motor and gears to vary the stiffness of the stabilizer bar when needed for cornering. The ability of these systems to make instant corrections is nothing short of impressive with the outstanding handling characteristics they make possible.
Electronically disconnecting stabilizer bars – popular on some new trucks and SUVs – use gearing similar to that in a manual transmission to physically disconnect the two halves of a stabilizer bar to allow maximum suspension movement. They will reconnect only once the vehicle is on level ground. Stabilizer bars are a fundamental part of suspension design and operation, and technology has made them even better. That’s something we all can “handle.”
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By Counterman
Platform-sharing” and “badge engineering” are terms often used to describe the common industry practice of developing multiple vehicle models from a common design. The economy of a single design underpinning multiple vehicles allows manufacturers to streamline the development process, and to provide the buyer with options across their base, mid-line and luxury divisions. Much of this “twinning” occurs within a manufacturer’s “family” of brands, but cooperating with rival manufacturers already well-established in a market allows the manufacturer to produce vehicles outside their wheelhouse.
Ford Motor Co. has a long history of platform-sharing among its Ford, Lincoln and Mercury divisions, in addition to several collaborations with outside OEMs. As a global company for more than 100 years, Ford’s U.S. arm also has benefitted from the engineering of its European, Australian and Asian divisions.
Since its establishment in 1939, Mercury was positioned as Ford’s mid-range division, filling the price gap between the Fords and Lincolns. Mercury served this role until 2010, when the division was shuttered. The last Mercury rolled off the assembly line in January 2011. That final Grand Marquis had shared the Panther platform with the Ford Crown Victoria and the Lincoln Town Car – two models that also would be discontinued later that year. Prior to its closure, Mercury also had offered mid-range versions of the Mustang (Capri), Taurus (Sable), Escape (Mariner) and Explorer (Mountaineer).
Rebadging the Explorer has been a cottage industry for Ford. In addition to the Mountaineer, Lincoln offered the Aviator from 2003 to 2005, the MKT from 2010 to 2019 and the Aviator again beginning in 2020 (now based on the latest Explorer CD6 platform). After prior collaborations on Ford’s Courier and Ranger pickups, Mazda also was an early adopter of the first-generation Explorer platform. The Mazda Navajo was built alongside the Explorer in Louisville, Kentucky, from 1991 to 1994. Mazda and Ford later would co-develop the Tribute and Escape for 2001.
This kind of sharing hasn’t always been the case at Ford. At the end of World War II, Ford of Canada divided up its dealer networks, establishing standalone “Ford” or “Lincoln-Mercury” dealers throughout Canada. An unforeseen outcome of this separation was that the Lincoln-Mercury dealers did not have economy models or trucks. In 1947, these dealers received the first of the “M-series” trucks, which essentially were re-badged F-series Fords. A budget line of “Meteor” passenger cars was introduced in 1949. Ford dealers received the “Monarch” line of mid-priced vehicles to fill the gap in their own lineups. This arrangement continued until the 1960s, when tariffs on vehicle trade across our northern border were eliminated.
Mercury trucks were never sold in the United States, but in 1993, Mercury buyers were offered their first minivan, the Villager. This actually was a joint venture between Ford and Nissan, with Nissan-badged versions carrying the Quest nameplate. The Villager was assembled by Ford, but featured a 3-liter Nissan FWD drivetrain. It later would be replaced by the Windstar, which had no equivalent Mercury companion model at the time. The Windstar was renamed the Freestar for 2004, and regained a Mercury companion in the Monterey.
Lincoln, founded in 1917 and purchased by Ford in 1922, still represents Ford’s luxury division. Long known for large cars like the Continental and the Town Car, Lincoln in 2021 transitioned exclusively to crossover and SUV platforms. Lincoln had even tried its hand at pickup trucks, with the 2002 Blackwood, and the 2006-2008 Mark LT. Both were rebranded luxury versions of the F-150 crew cab platform.
In 2007, Lincoln adopted a new model-naming convention, playing on the heritage of the “Mark-series” nameplate used through 1998. The MKX and MKZ were the first of these, with the MKZ sedan being the Lincoln version of the Ford Fusion and Mercury Milan, and the MKX being a Ford Edge-based crossover (“X”-over). Originally intended to be spoken as “Mark-X” and “Mark-Z,” both vehicles were produced on the same CD3 platform originally developed for the Mazda 6. The MKS sedan (based on the Taurus) and the full-size Explorer-based MKT followed in 2009 and 2010, respectively.
In 2015, the MKC compact crossover was introduced, built on the Escape platform. Lincoln has since dropped the “MK” designations in favor of proper names for its crossover and SUV lineup, which is a relief to anyone who has misheard or misspoken these similar-sounding model names while looking up parts!
Ford-Lincoln-Mercury (FLM) dealerships once were a common sight here, with all three divisions available in one location. But, after a decade without Mercury, Ford-Lincoln dealers are fracturing yet again. In 2019, Lincoln began an initiative to develop standalone Lincoln dealerships to market more exclusively to the upscale clientele of the luxury-car market. Targeting 30 U.S. metro areas, Lincoln-only showrooms have already opened in half of the roughly 150 planned locations. Sales are up at these dealerships, but they still don’t have pickup trucks!
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