The Anti-Roll ( Sway- ) Bar
A very simplified description of the anti-roll bar is an extended U-shaped metal bar between the suspension system, of both wheels on an axle. The "U"-bar bottom part is secured to the frame with bushings that allows the bar to twist and turn. The bar's task is to reduce body lean and keeps the vehicle in a horizontal position related to the ground.
Basically the Anti-Roll Bar is nothing BUT a safety feature, which primary task is to stiffen up the suspension when needed to reduce roll / tilt of the vehicle. A "side-effect" is that it also makes the vehicle stand in a horizontal position related to the ground.
The suspension itself, without the Anti-Roll Bar, works against the driver while cornering at high speed and in critical situations like avoiding maneuvers.
Imagine you need to make a hard left turn at a speed of "only" 50km/h.
The law of physics will force the vehicle to start leaning right, and the front suspension on that side cannot withstand the forces it's exposed to and the front right side of the vehicle is forced DOWN.
At the same time the inner- / lightened- side ( left ) side suspension is extended by the shock absorber, as it tries to keep the wheel in contact with the ground. The combined force of the suspension and the shock absorber will push the front left side of the vehicle UP, compressing the right side further which in turn lightens the left side more....
Without anything limiting the suspension at that speed in a critical moment, its easy to see.. the suspension would actively help the law of physics to turn over the vehicle.
The speed 50km/h doesn't seem high enough to turn over the car, but the fact is that if the suspension is in good condition the car WILL turn over at 50km/h.. and even at lower speeds.
Same speed and turn as above.
When the right side suspension is compressed to a certain limit, the Anti-Roll Bar connected between the sides, counteracts the natural movement of the left side suspension by compressing it. Thus forcing the left side suspension to follow the right side DOWN.
Both side cooperate to keep the vehicle levelled final result is that instead of the suspension actively tilting the vehicle, the suspension of both sides is pulled DOWN and results in With the Anti-Roll Bar the This means that instead of tilting the vehicle
There are different practical solutions to this function of the vehicle, but the basic principles are the same. The anti-roll bar itself is a metal bar and is not likely to fail, but its mounting bushes can fail.
The bar is connected to the suspension parts via end-links or drop-links with ball joints, which frequently fails.
Different symptoms and how to determine a possible fault in the Anti-Roll Bar system can be found further down.
As far as i know, a faulty anti-roll bar end link / drop link is a MOT failure in any country, and if not.. it should be - for your and your loved ones safety.
Fixing a faulty drop link is an easy DIY-fix that require very few tools.
Further down is a link to a page describing how to change the drop-link.
Those who remember the introduction year of Mercedes A-type ( Baby Benz ) might remember the headlines when a motor-magazine test crew found themselves upside down after doing an avoiding-maneuver ( moose- ) test, at a speed not higher than 60 km/h ( 38 mph ).
The motor-magazine blamed the Anti-Roll system of the brand new Mercedes model, and classified it as "DANGEROUS".
Mercedes initially denied the problem, accusing the motor-magazine of performing an "unlikely scenario"-test. The motor-magazine stated that braking and steering hard, is what the driver would/should do to avoid an accident like colliding with a moose ( an animal bigger than a horse).
The debate between Mercedes and the motor-magazine got world wide publicity, and the term moose-test was born..
After initially denying any problem with the Baby-Benz, Mercedes announced a call-back of all sold units and made changes to.... you guessed it... the anti-roll system.
The anti-roll bar and it's links should have NO play what so ever. If you can feel even the slightest play in the end link ball joints, the end link is faulty and should be replaced.
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