What is a drop link?
A drop link (US: sway bar link) is a short rod with a ball joint at each end that connects the anti-roll bar to the suspension, so the bar can resist body roll in corners. Worn drop links are the most common cause of a light knock from the front of a car over rough roads.
US sway bar link Also called anti-roll bar link, stabiliser link
- Drop link US: Sway bar link
- Anti-roll bar US: Sway bar
- Strut body
- Track control arm US: Lower control arm
What does a drop link do?
It connects the end of the anti-roll bar to the suspension: in the app's MacPherson strut model, from a tab on the strut down to the bar. A small ball joint at each end lets it tilt as the wheel rises and turn as the strut steers.
The anti-roll bar does nothing while both wheels rise together. In a corner the outer wheel rises and the inner one drops, the links twist the bar, and its resistance keeps the body flatter. So the links carry the bar's force every time the car leans, and that is what wears their ball joints.
What are the signs of a worn drop link?
- A light knock or rattle over broken roads. Loudest at low speed over potholes, speed bumps and rough surfaces, from the corner with the worn link. What causes a knocking noise over bumps?
- A clunk as the car rolls into a corner. Free play in the worn joints lets the bar move before it pushes back.
- Play you can feel by hand. With the car safely raised, grip the link and rock it. A good link has no free movement and makes no knock.
- A split boot or rust at a ball joint. Once water and grit get in, the joint wears quickly.
- More lean in corners. If a link breaks, the bar stops working on that side and the car rolls more.
Can you drive with a broken drop link?
Fix it soon
Usually, for a short while and with care. The drop link does not hold the car up or steer it, so the wheel stays where it should. But with a broken link the anti-roll bar stops working on that side: the car leans more in corners and is less settled in a sudden swerve, and a loose link can rattle against the strut. Have it replaced soon. A badly worn or broken link can fail an MOT.
Why do drop links wear out?
Each end has a ball held in a lined socket under a rubber boot. Every time the car leans, the joints rock under load, and on rough roads they take short, sharp hits. Over the years the socket wears, the ball gains a little free play, and the play shows up as a knock whenever the bar is loaded and unloaded.
A split boot speeds this up, because water and grit get into the socket. That is why a look at the boots is part of every suspension check, and why a link with a torn boot is worth replacing before it starts to knock.
What does replacing a drop link involve?
- Time
- About 30 minutes
- Difficulty
- Straightforward
- Parts
-
- A new drop link with its two nuts
- Park on level ground, chock the wheels and loosen the wheel nuts, then raise the car onto an axle stand and take the wheel off.
- Jack under the track control arm just enough to take the twist out of the anti-roll bar, so the link is no longer loaded.
- Undo the nut at each end while a hex key in the tip of the ball stud stops the ball spinning in its socket.
- Lift the old link out and check it: play or a knock in either ball joint, or a split boot, confirms it was worn.
- Fit the new link, run its nuts on while holding each stud the same way, and tighten them.
- Lower the jack from the arm, refit the wheel, lower the car and tighten the wheel nuts in a star pattern. Check them again after about 30 miles.
Tools
- Wheel chocks
- Breaker bar
- Socket and ratchet
- Trolley jack (US: Floor jack)
- Axle stand (US: Jack stand)
- Flat screwdriver (US: Flat-blade screwdriver)
- Ring spanner (US: Box-end wrench)
- Hex key (US: Allen key)
- Torque wrench
- Crow's-foot spanner (US: Crowfoot wrench)
Work safely
- Work on firm, level ground with the handbrake on and the other wheels chocked.
- Never work under a car held only by a jack: set it on an axle stand.
Tighten every nut and bolt to the figure in the maker's manual for your car.
One of the easier suspension repairs. Many garages change both links on an axle at once, and a new link does not change the wheel alignment.
Questions people ask
Is a drop link the same as an anti-roll bar link?
Yes. Drop link, anti-roll bar link and stabiliser link are UK names for the same part. In the US it is a sway bar link, or an end link.
How long does a drop link last?
There is no service interval: links are replaced when they wear, which can be anything from a few years to the life of the car, depending on the roads. Potholes and a split boot shorten their life the most.
Should drop links be replaced in pairs?
It is not essential. A single new link does not unbalance the car the way a single new spring or damper would, but the other side has done the same miles, so many garages change both at once.
Do you need a wheel alignment after replacing a drop link?
No. The link only connects the anti-roll bar to the suspension and sets none of the wheel angles, so the alignment is unchanged.
Why does the ball stud spin when you undo the nut?
Because the ball turns freely in its socket. Hold the stud still with a hex key in the socket in its tip, or a spanner on its flats where it has them, while you turn the nut.
Related
Symptoms
- What causes a knocking noise over bumps? A knocking or clunking noise over bumps usually comes from a worn joint in the front suspension.
Parts nearby
- What do control arm bushes do? Control arm bushes (US: bushings) are the rubber mountings where a control arm pivots on the subframe.
- What does a ball joint do? A ball joint is the ball-and-socket joint that connects a suspension arm to the wheel's steering knuckle.
- What does a coil spring do? A coil spring holds the car up. Each corner rests on one, and when the wheel hits a bump the spring compresses, stores the energy and pushes the wheel back down, while its length sets the ride height.
- What does a shock absorber do? A shock absorber (US: shock) controls the spring. Without it the car would keep bouncing after every bump; with it, the body settles after one movement and the tyre stays pressed on the road.
The whole system
- How does a MacPherson strut work? The MacPherson strut, part by part, with an interactive diagram.
