Maintaining Control
When suspension bushings go bad, ride quality and vehicle control characteristics are compromised—for service tips, read on.
Suspension bushings allow for the smooth movement of suspension components on both the front and rear of a vehicle. Bushings are found at the connection points for control arms, trailing links and other components. Bushings are also used to isolate mounting points for suspension components, such as stabilizer bars. Because bushings are exposed to the elements, deterioration of the bushing material is always a possibility. And when bushings go bad, ride quality and vehicle stability are compromised.
BUSHING BASICS
A bushing is a device that isolates vibration and harshness between two components linked by a fastener. On a passenger vehicle, a bushing is usually made from rubber, or similar material. It usually has a steel sleeve, which is bonded to the rubber, through which the mounting bolt passes. The bushing will be bonded, in many cases, to the component into which it is installed. Figure 1 illustrates the mounting of a control arm (callout 2) in the front suspension cradle crossmember (callout 3). The pivot, or mounting, bolt (callout 1) passes through both the control arm and cradle crossmember. The bushing (not seen) is installed in the control arm and the pivot bolt passes through it.
As the control arm moves due to normal vehicle motion, the vibration and harshness from the road is transmitted from the wheel assembly through the control arm to the frame. On a passenger vehicle, a relatively soft material is used in the control arm bushing, and other bushings on the car, to absorb much of these road effects. In street performance vehicles, such as an SRT® vehicle, the bushing will be made from a harder material to increase the handling characteristics. On the downside, more vibration and harshness is transmitted to the vehicle and felt by the passengers. In the end, the bushing material selected is a compromise between handling characteristics and passenger comfort.
Stabilizer bar bushings, as seen in Figure 2, are stand alone components that have neither a steel sleeve, nor are bonded to a suspension component. Such a bushing is slit to allow it to fit over the stabilizer bar. A retaining bracket is fit over the bushing and mounted to a crossmember or other section of the subframe. The bushing isolates the stabilizer bar from its mounting surface to prevent metal-to-metal contact, greatly reducing vibration and harshness. These bushings are relatively easy to service (more on this later).
On vehicles such as Chrysler PT Cruisers and minivans, the front suspension is rather simple. There is a lower control arm with two mounting points that have bushings. There’s a vertical link with bushings on each connection end (one end is connected to the McPherson strut; the other end to the crossmember). Plus there are the two mounting bushings similar to those shown in Figure 2.
But other vehicles have much more complex front suspensions. A perfect example is the LX platform used for the Chrysler 300, Dodge Charger and Dodge Magnum. This vehicle platform utilizes a long and short arm design which has an upper and lower control arm, plus a tension strut and a stabilizer bar with a vertical link. There are several more bushings used on this suspension than the one used on the minivan and PT Cruiser. While the handling characteristics are better with this design, there are more bushings that might fail over the life of the vehicle. The same differences can be seen on the rear suspensions, too.
INSPECTING SUSPENSION BUSHINGS
How do you know a suspension bushing is bad and requires replacement? Quite often, your customer will complain of noise, such as a clunk or thud, when going over a pothole or bump in the road. Inspection will confirm which bushing is bad.
Raise the vehicle on a lift and closely examine each bushing. If possible, look for small cracks or other signs of deterioration in the bushing material. If these signs are seen, it is suggested to replace the bushing. When the bushing has failed, tears in the material will clearly be evident. Also, you should be able to see where the bond between the bushing and the component has separated.
SERVICING SUSPENSION BUSHINGS
Before you think about servicing a particular bushing, be sure that the bushing can be serviced. In many cases, if the bushing is bad, the entire control arm must be replaced. This is the case with the minivans and PT Cruiser in which the front bushing is not serviceable, but the rear bushing is. Both bushings on the front lower control arm on the Jeep® Compass, Jeep Patriot and Dodge Caliber are not serviceable, requiring replacement of the control arm. The same applies to the rear suspension.
On front suspensions, replacing a control arm bushing, or the control arm itself, will require the removal of the control arm. Let’s review the basic steps for a suspension with a lower control arm and stabilizer bar, such as the Compass/Patriot/Caliber:
1. Raise and support the vehicle
2. Remove the tire and wheel assembly
3. Remove the pinch bolt clamping the ball joint to the steering knuckle
4. Separate the ball joint stud from the knuckle using the appropriate prying tool; pry down on the lower control arm and up against the ball joint boss Caution: After the ball joint has been separated from the knuckle, don’t pull forward on the steering knuckle; this action can separate the inner CV joint from the halfshaft
5. Remove the pivot bolt from the front control arm bushing
6. Remove the pivot bolt from the rear control arm bushing
7. Remove the control arm from the crossmember
If one or both of the bushings can be serviced, it is likely that special tools will be required. For instance, on the PT Cruiser a special receiver (steel plug) and large C-type screw clamp are needed to press the old bushing out and the new one in. Some bushings are pressed out (and in) using a hydraulic press. Check the appropriate Chrysler service manual for the special tools that are needed.
Figure 3 shows the special tools used to remove the bushing on the front control arm on the LH models—1993–2004 Chrysler Concorde, Chrysler LHS, Chrysler New Yorker, Chrysler 300M, Dodge Intrepid and Eagle Vision. The arbor press ram (callout 1) pushes special tool 6644-2 (callout 2) on the bushing (callout 4). As the bushing is pressed out of the control arm, it falls into the receiver (callout 3).
Stabilizer bars are used on virtually all passenger vehicles. Replacing the bushings merits some consideration as this procedure is somewhat common. While it might seem that replacing these bushings is easy, there are several points to keep in mind.
First of all, be sure that the bushing is oriented correctly (look for orientation marks on the bushing). Or, in the case of the LH models, the slit in the bushing must be facing forward. Secondly, position the stabilizer bar correctly to prevent contact with other suspension components. Then, position the retainers and install the retaining bolts. On some vehicles, the bushings have a ridge which must be inserted into a recess in the retainer (or, the bushing has a recess that must be fit into a ridge on the retainer). Finally, properly torque the retaining bolts to properly secure the stabilizer bar.
