Chassis Parts Overview - Tire Review Magazine

Chassis Parts Overview

The demand for replacement chassis parts has remained fairly steady in recent years. The demand for replacement parts is a function of vehicle age and miles driven. In a soft economy, people are keeping their vehicles longer than ever before. The average age of all cars and light trucks today is at an all-time high of 10.6 years, with nearly one out of every five vehicles being more than 15 years old. To keep these aging vehicles roadworthy, motorists are spending money on necessary repairs — and that includes replacing worn chassis parts.

Ball Joints
Ball joints have been around since the 1950s and have long been seen as a high-mileage replacement part. Ball joints connect the control arms to the steering knuckles and allow the knuckles to turn. On most cars and light trucks that have SLA (short long arm) suspensions, there are two upper and two lower ball joints in the front suspension. Cars with wishbone strut suspensions also have upper and lower ball joints, but on cars, minivans, CUVs and SUVs that have strut suspensions there are only two lower ball joints (one for each side).

Over time, the constant pounding that occurs with every bump and dip in the road produces wear and play in the ball joints. Load-bearing ball joints typically experience the most wear. These are usually the lower ball joints on most vehicles with SLA suspensions, but may be the upper joints on some older vehicles where the spring is mounted over the upper control arm. Eventually, the joints loosen up and become noisy, making a bonking or clunking noise every time the vehicle drives over a bump. Play in a worn ball joint can also allow unwanted alignment changes that increase tire wear and steering stability. In a worst case scenario, a badly worn ball joint may fail and pull apart causing the control arm to separate from the steering knuckle. If this happens, the suspension will collapse and the driver may lose steering control. Should this happen at highway speed, it could have potentially deadly results.

Ball joint wear can be diagnosed by raising the wheels off the ground and using a pry bar to see how much the joint moves when moderate force is exerted against the control arm. If play exceeds specifications, the joint is worn and needs to be replaced. The question is, should only the worn joint be replaced, or should all of the ball joints be replaced?

Chances are if one joint is worn beyond acceptable tolerances, the companion joint on the opposite side is also nearing the end of its useful service life. If a vehicle with a SLA suspension has a LOT of miles on it (say more than 150,000), chances are all four joints are probably showing considerable wear and may be close to their maximum acceptable wear limits. That’s why most professional technicians recommend replacing all of the ball joints at the same time even if only one has exceeded acceptable wear limits. Do the job once and the vehicle owner won’t have to worry about what might happen down the road.

Replacing a ball joint used to be a fairly straightforward repair job. The old joint would be unbolted or pressed out of the control arm and replaced with a new joint. On some older vehicles, the ball joints are riveted in place, so the rivets have to be drilled out and replaced with bolts. But on a growing number of late-model cars and trucks, “unitized” aluminum control arms are used where the ball joint is an integral part of the control arm assembly. On most of these applications, the entire control arm assembly must be replaced with a “loaded” control arm if the ball joint is worn out — unless the arm uses a pressed-in ball joint that can be removed and replaced with an aftermarket ball joint.

On 2005 to 2007 Cadillac STS and 2004 to 2007 Cadillac SRX models, a unitized upper control arm is used and no replacement ball joint is available from a GM dealer. It’s the same story for the lower control arm on Dodge Caliber and Jeep Compass models. The unitized control arm has a pressed-in ball joint but no replacement joint is available from the dealer. However, on these applications it is possible to remove the ball joint from the arm and to replace it with an aftermarket ball joint. Or, if the customer desires, the original arm can be replaced with an aftermarket unitized arm.

In some cases, the aftermarket replacement parts have been re-engineered to overcome weaknesses in the OEM design. On 2007 to 2011 GM full-size light duty pickup trucks and SUVs, a unitized upper control arm is used in the front suspension that has a sealed (non-greaseable) ball joint with a low-friction polymer bushing. Depending on how the vehicle is used, the factory ball joint can be prone to premature failure in as little as 36,000 miles. On 1995 to 2004 Ford light trucks and SUVs (Explorer, Ranger, Expedition, F150, etc.), Ford uses a similar setup with unitized upper control arms. For these applications, aftermarket replacement control arms are available that include more durable greaseable ball joints with metal gusher bearings.

Here’s another example of how aftermarket chassis parts can often save your customers money, time and trouble. On Honda Element SUVs, the ball joint is part of the steering knuckle. Honda does not offer a replacement ball joint separately and wants to sell their customers an entire steering knuckle assembly. However, it is possible to replace the ball joint separately with a special aftermarket ball joint that has a knurled outer housing so it can be press fit into the knuckle.

Loaded Control Arms

Loaded control arms, like preassembled ready-to-install struts, have become popular with both professional installers and DIYers. Growth in this product category is up 25 percent year over year. Why? Because the vehicle manufacturers are using more unitized control arms, and loaded replacement control arms are much faster and easier to install than trying to replace the joint and bushings separately. They also reduce the number of SKUs you have to inventory by having one part number for the arm instead of separate part numbers for an arm, bushings and ball joint. And as we just described, many of the aftermarket replacement arms offer improved durability over the original parts.

With a conventional control arm, a hydraulic press may be required to remove and install the ball joint on the arm. Or, there may be some drilling or grinding required to replace the old joint. A press or bushing tool is also necessary to push the old bushings out of the control arm pivots and to squeeze in the new ones. And there is always the possibility that the person who is doing the job may not do it correctly. A loaded control arm that comes with new bushings and ball joint preinstalled eliminates such problems and makes the job much easier, faster and more profitable. The total cost of the repair is still about the same although the labor portion of the bill is usually less. But overall productivity and profitability go up because of the faster turn around in completing the repair.

Changes in Technology
Though chassis parts are still hard parts that have not been affected by the electronic revolution, they have undergone some technical changes that your customers need to be aware of. A growing number of ball joints (and tie rod ends) now use Torque-To-Yield (TTY) studs and fasteners. You’ll even find TTY fasteners on some shock mounts, bushings and control arms. What’s the difference? A TTY fastener is designed to stretch slightly when it is tightened to apply a more consistent clamping load. Its metallurgy and heat treatment is different from that of an ordinary fastener. Consequently, TTY fasteners must be tightened to exact specifications using a special procedure.

Tightening a TTY fastener usually involves tightening the fastener with a torque wrench to a specified value, then giving it an additional twist to a specified number of degrees of rotation so it will achieve proper stretch and loading. For example, the installation spec might call for tightening the fastener to 15 to 30 ft.-lbs., then giving it an additional 140 to 225 degrees of twist. If this is not done correctly, the fastener may be over tightened and fail. What’s more, many TTY fasteners are designed for one-time use only and should not be used a second time because of the risk of breakage. The threads must also be dry (no oil or grease), otherwise it may be over tightened and break.

If someone who is replacing a TTY ball joint or tie rod end is not aware of this, and uses an impact wrench to zip down the stud nut or fasteners, they may end up over-stretching or breaking a TTY fastener. For this reason, it’s important to always refer to the vehicle service literature for any special installation instructions or procedures. TTY ball joints can sometimes be identified by an inset hex head at the end of the ball stud (but not always).

Another installation precaution that applies to all types of ball joints is to make sure the taper in the steering knuckle is not out-of-round, cracked or damaged. Problems here can lead to broken ball studs down the road. If the hole is bad, the knuckle needs to be replaced.

A related product a DIY customer may require is a ball joint separator or fork tool to separate the old ball joint from the knuckle.

Tie Rod Ends

Tie rod ends are also a frequently replaced chassis part (though technically it is part of the steering linkage). Worn tie rod ends can cause steering play and accelerated tire wear. The wear limits for most tie rod ends allow for little or no visible play. On many vehicles, the right tie rod end may wear out before the left tie rod end. This may be attributed to the fact that right hand turns are usually sharper than left turns, so the right tie rod end undergoes more movement and wear as the miles add up.

As is the case with ball joints, when one tie rod end wears out, chances are the tie rod end on the opposite side is also nearing the end of the road. Replacing both at the same time is often recommended to eliminate play in the steering linkage and restore proper steering control. Ditto for the inner tie rod ends on vehicles that have them, and inner tie rod sockets on vehicles with rack & pinion steering.

Left and right tie rod ends may be different, so make sure you look up the correct part number for the application. The threads are also different (right and left handed) so make sure your customer is aware which tie rod end fits which side BEFORE they attempt to install the parts. A related sales opportunity for DIY customers would a tie rod separator tool that may be needed to remove the old tie rod ends.

Other Chassis Parts
Idler arms, steering links, sway bars and bushings, and springs are also commonly replaced steering and suspension parts. Play in steering linkage components will typically result in steering wander and looseness as well as accelerated toe wear on the tires. Play in control arm bushings will often upset camber/caster alignment and can result in a steering pull and shoulder wear on the tires.

Play in sway bar bushings often cause suspension noise. On 2001 to 2007 Chrysler minivans, the factory sway bar bushings can wear prematurely and become noisy. Some aftermarket replacement sway bar bushings are wider than the original bushings to provide more support, and are mode of more durable materials that better resist deformation and deterioration.

Springs are an often overlooked chassis part that may need to be replaced. All springs sag somewhat with age, but some sag more than others. If ride height is out of specifications, it can upset wheel alignment and cause steering and tire wear problems.

Spring failures have plagued some late-model cars, such as 2000 to 2007 Ford Focus models. To save weight, the coil springs on many late-model cars are made with thinner diameter wire and with fewer turns per spring. The trade-off is that corrosion can penetrate the spring coating and create stress points that eventually lead to hairline fractures and spring breakage. Some aftermarket replacement springs are made with heavier gauge wire and include more coils per spring to reduce stress and risk of spring failure.

If a customer needs a replacement spring, replacing springs in pairs is usually recommended to maintain proper ride height side-to-side. DIY customers may also need to buy or rent a spring compressor to change a spring. A customer may also want to upgrade their original springs by replacing them with variable rate springs if they tow a trailer or haul heavy loads.

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