The control arm bushing consists of an outer metal sleeve, a durable rubber bushing and an inner metal sleeve. It's attached to the ends of the control arm as it's supported to the frame of the vehicle. Without the bushing, the metal ends of the control arm would be mounted to the frame and cause metal-to-metal contact. This would cause major clunking as the suspension manoeuvres over bumps and other deviations on the roads. The bushing acts as a hinged dampener to cushion the suspension and provide a more manageable and quiet ride. Most front-wheel drive cars that employ struts only use a lower control arm, but many trucks and SUVs have an upper and lower control arm.
Upper control arm bushings are a little bit easier to inspect than lower ones. Peeking through the wheel well of each front wheel usually gives you a clear view to the bushings. In some cases, you can also inspect them from the engine compartment and look down on each side of the engine by the wheel.
Because rubber cracks and dry rots over time, look for signs of this symptom--although if it's just starting to dry rot and crack on the outer edges, it doesn't necessarily mean it needs to be replaced. The control arm ends should be perfectly centred inside the bushing to buffer it around the full diameter. A compromised bushing begins to weaken on the side that endures the most stress from the suspension.
The lower control arm bushings are usually encased between the end of the control arm and the side of the car frame, making them difficult to see. A large pry bar can be used to pry the control arm one way or the other. A good bushing returns the control arm to its original position when the pry bar is removed. A compromised bushing causes the control arm to stay in the position the pry bar moved it toward.
Deterioration of the Control Arm Bushing
When the bushings deteriorate, they affect alignment and vehicle handling. Wheel alignments are set in minor degrees, and it doesn't take much to position the tire at an awkward angle. All suspension components work in unison to position the tire as flat and straight onto the road as possible. A worn control arm bushing affects the camber angle of the tire. Camber is the vertical angle of the tire. When this is compromised, the tire cannot hit the road flatly. It's angled slightly enough to begin to wear the edge of the tire that contacts the road first. This not only causes excessive premature tire wear, it affects the way the vehicle steers. It may pull slightly or aggressively, depending on the severity of the bushing wear, to one side.
Worn bushings also allow metal-to-metal contact that they're intended to buffer when going over bumps. The suspension being compromised also affects the manageability of the vehicle when stress is placed on it.
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