What Is The Function Of Control Arm Bushings?
To understand the function of control arm bushings, we first need to understand what control arms are, and what they do. Put simply, front-end control arms perform two functions, the first being that the control arms form one leg of the suspension cradle that suspends the vehicle between the front wheels. The second function of control arms is to form a link between the vehicle frame and the steering knuckle to provide multiple pivot points for the suspension to absorb bumps in the road, and to allow the front wheels to be steered.
On rear suspension systems, control arms are often referred to by different names, the most common being drag links, trailing links, and transverse links. However, regardless of the name, rear control arms have the tasks of maintaining the position of the rear axle relative to the thrust line of the vehicle, maintaining individual real-wheel alignments, as well as to form part of the rear suspension cradle that suspends the vehicle between the rear wheels.
Given the above, it should be obvious that control arms transmit both vibrations caused by bad roads and suspension movements to the vehicle frame that would be intolerable if the control arms were not fitted with resilient bushings designed to absorb most of the vibration and shock loads caused by uneven road surfaces.
As a practical matter, and if the control arm bushings are in good condition, they will be pliant enough to allow the suspension to travel unimpeded throughout its maximum travel in both directions, i.e., up and down, as well as being compressible enough to absorb vibrations that would otherwise have been transmitted to the vehicle frame.
However, a third requirement is that control arm bushings must be resilient enough to endure the continual flexing, stretching, vibration, and heat that come with modern driving conditions for a reasonable period of time; reasonable in this context typically being several years of average driving mileage.
Common Symptoms of Faulty Control Arm Bushings
It should be noted that worn, damaged, or broken control arm bushings produce different effects and symptoms on different vehicles not only because of the differences in suspension designs and configurations, but also because vehicles are used differently, or for different purposes. Nonetheless, some symptoms are common to all vehicles, but be aware that the severity of some symptoms listed here may vary between makes and models.
Uneven Tire Wear
This may occur as the result of the front wheels being unable to maintain proper alignment, but note that accelerated wear usually occurs on the inside shoulders of the tires if control arm bushings are worn or damaged.
Vehicle May Pull To One Side
This can occur as the result of the front wheels being unable to maintain proper alignment on uneven road surfaces.
Steering May Snap To One Side When Brakes Are Applied
This typically happens when the control arm bushings on only one side of the vehicle are worn or damaged. When the brakes are applied, the free play in the worn/damaged bushings forces the affected wheel out of alignment.
Difficulty Maintaining Directional Control Even At Moderate Speeds
Since control arms are also used to maintain wheel alignment, worn/damaged control arm bushings can force one or more wheels out of alignment, which has a direct bearing on straight line tracking.
Steering May Feel Sloppy
If control arm bushings are severely worn or damaged, the excessive free play can mimic steering inputs, since the front wheels are unable to maintain their alignment relative to each other. Only in this case, the “steering inputs” due to the free play are uncontrolled (and often uncontrollable), since corrective steering inputs are mostly absorbed by the excessive free play in the worn bushings.
Counter Steering May Become Necessary
Since rear control arms control the alignment and position of the rear axle, worn bushings can force the rear of the vehicle out of alignment relative to the front wheels, which in turn, applies a steering input to the rear axle that may require a measure of counter steering to correct or counteract. In other words, you may have to turn your steering wheel slightly to keep driving straight.
Knocking, Thudding, or Thumping Noises On Rough or Uneven Road Surfaces
The severity of knocking sounds depends on the degree to which the bushings are worn, but in general, these sounds are the result of a worn or broken bushing failing to absorb shock loads, thus allowing direct metal-to-metal contact between the control arm and the vehicle frame.
Replacing Control Arm Bushings
While control arm bushings can be replaced on a DIY basis, this procedure is not recommended for novice non-professional mechanics that do not possess the required skills or have access to the required tools and equipment. Note that one such required piece of equipment is a vertical press with which to remove the old bushings from the control arm, and to press the replacement bushings into the control arm to prevent damaging the replacement bushings. If you don’t have a press, most shops will do this step for you for a few bucks if you bring them the parts.
Note: The example steps below are intended for general informational purposes solely to help give you an idea of project difficulty and tools required. As all cars are engineered differently, repair procedures and safety hazards vary from vehicle to vehicle. To ensure that you have a vehicle specific repair procedure and an exhaustive list of potential safety hazards, we advise you reference a factory service manual for your vehicle. Similarly, referencing a repair manual such as Chilton or Haynes might serve as a less expensive alternative.
Step 1 – Lift the vehicle off the ground with a suitably rated floor jack and support the vehicle with properly rated jack stands.
Step 2 – Remove the wheels using a lug wrench or an impact wrench, and place them out of the way.
Step 3 – If the vehicle is fitted with McPherson struts, locate the sway bar and drop link that connects the sway bar to the control arm. Detach the drop link at the control arm.
Step 3.1 – Remove the nut holding the ball joint in place and use a ball joint extractor to pull the tapered section of the ball joint out of the steering knuckle. Note though that this step is often difficult and time consuming.
Step 3.2 – Locate the brackets holding the control arm to the floor pan and remove all bolts using the ratchet from your socket set. Note the length of each bolt as it is removed, since replacing the wrong bolts in the wrong hole can cause the control arm to separate from the vehicle during operation.
Step 3.3 – Remove the control arm from the vehicle and use the press to remove the old bushings. If a press is not available, you can usually have this done at a local machine shop or mechanic for a few bucks if you bring the parts. However, note that some control arm bushings have to be inserted in a specific way so note all markings and make sure that the replacement bushings are installed according to these markings. Failure to observe this very important point will result in premature failure of the new bushings.
Step 3.4 – Reassemble all parts in the exact reverse order of removal and make sure all bolts are properly torqued down to the vehicle manufacturer’s specification using a calibrated torque wrench.
Step 4 – If the vehicle is fitted with upper and lower control arms, use a set of coil spring compressors to compress the coil spring. Remove the compressed coil spring from the vehicle and place it aside in such a manner that the spring compressors cannot be disturbed or knocked loose. It should be noted that this is a potentially dangerous step, and serious personal injury, or even death could result if you get it wrong due to the amount of stored energy in the springs. If you do not have full confidence in your ability to perform this step safely, refer the vehicle to a competent repair facility for professional assistance.
Step 4.1 – Remove both ball joints from the control arms as per Step 3.1, but take suitable precautions to prevent the steering knuckle falling to the ground, which could damage brake components.
Step 4.2 – Remove the control arms from the vehicle as per Step 3.2
Step 4.3 – Remove the old bushings, and fit the replacements into the control arms. See Step 3.3.
Step 4.4 – Reassemble all parts in the exact reverse order of removal but take extreme care when reinstalling the coil spring. Note that if the compressing tools slip off the spring during installation, the coil spring could expand with sufficient explosive force to cause severe injury or even death.
Step 5 – Make sure all bolts are torqued down properly using a torque wrench before lowering the vehicle to the ground.
NOTE: Overall, it is often easier, safer, and more cost effective to purchase and fit new control arms with the bushings already fitted. See the section below for details on suppliers that have been supplying high quality, replacement control arms and control arm bushings that often exceed OEM specifications.
Best Control Arm Bushing Brands
Moog
Moog is the official supplier of steering and suspension components, including control arm bushings, to NASCAR, which is arguably the highest recommendation any parts supplier can boast.
Nonetheless, control arm bushings supplied by Moog have a long history of outlasting both OEM and competing equipment. This is mainly the result of Moog’s commitment to designing parts that are easy to fit, which has a direct bearing on how well their products perform not only in terms of durability, but also in how well their control arm bushings smooth out even the roughest bumps in the road.
Click here to find Moog control arm bushings for your vehicle.
Mevotech
Mevotech prides itself on the fact that their products are designed to withstand tough Canadian driving conditions (so really rough roads), and unlike most OEM control arm bushings that usually consist of only rubber compounds, bushings made and supplied by Mevotech are made from polyurethane to provide superior resistance against corrosion and degradation caused by oil, road salt, and mud.
Click here to find Mevotech control arm bushings for your vehicle.
Energy Suspension
Energy Suspension is known for the fact that they have developed HYPER-FLEX, a range of variable, but fit-for-purpose polyurethane compounds that each suits a very specific need, requirement, or set of operating/driving conditions. No matter what you drive: a street racer, sedate urban run-around, a track racer, muscle car, or even a monster off-road truck, Energy Suspension can supply durable control arm bushings that are designed to provide superior ride comfort and improved steering response on your specific application.
Click here to find Energy Suspension control arm bushings for your vehicle.