A sway bar acts like a torsional spring that joins the right wheel to the left wheel on either the front or rear of the vehicle. If both wheels move vertically up and down at the same time, the sway bar does not activate or impart pressure. When the wheels move up and down independently of each other, such as in a hard turn to the left or right, the sway bar will resist the movement and try to maintain a stable condition between the wheels. The sway bar counteracts a vehicle's tendency to lean. A vehicle owner can diagnose a broken sway bar by knowing the signs and symptoms they produce.
The best way to find a broken sway bar involves a visual inspection of the suspension. The sway bar connects the lower control arm system to the mainframe rail. The sway bar looks like a thick, angled rod, with bushings on each end. A broken sway bar will hang down from one of its connecting joints. It can be seen more easily if the vehicle has been lifted up on jack stands. Pulling down on the sway bar will reveal if it has broken loose at either joint. This is true for both front and rear sway bars.
A broken sway will cause a condition known as "understeer." This happens as a result of the pressure loss on the suspension, leading to instability while driving. The effect of steering input will cause more force to turn the vehicle, affecting its "feel" or maneuverability. The vehicle will appear mushy or slow in recovering from even slight turns. A broken rear sway bar will not allow the rear wheels to track properly, resulting in a lag response, also affecting steering.
A broken sway bar on the front or rear will cause a condition called "roll-under." This happens during a tight, high-speed turn where one suspension spring compresses, which allows the opposite suspension spring to lift up. The sudden transfer of weight pushes down on the outboard tire, folding the sidewall under itself. The vehicle body and chassis will also shift and lean dangerously over, until it recovers from the turn. Sometimes the vehicle will recover and continue to sway from side to side.
A broken sway bar will also manifest itself while driving over an uneven or washboard-like road surface. A clanking or clunking sound will emanate from the front or rear suspension. Broken sway bars will emit knocking and scraping noises over potholes and dips, sometimes rhythmically. This happens when a sway bar bushing joint swings freely without support and strikes the chassis frame or control arm.
Any erratic vehicle handling in combination with loud metallic noises will point to a broken front or rear sway bar. Such handling characteristics will show up as swerving, excessive lean in turns, wandering, hard steering and a lightweight feel to the rear end of the vehicle. A broken rear sway bar can cause a noticeable "fishtail" condition, where the rear of vehicle leans excessively and rebounds from the front steering input.