What do sway bar bushings do?
Sway bar bushings (anti-roll bar bushes) are the rubber sleeves that hold the sway bar to the subframe or body, one on each side, each clamped by a bracket. The bar turns in them as the suspension moves, and the rubber keeps it from rattling. Worn ones squeak, creak or clunk over bumps and in corners.
UK anti-roll bar bushes Also called stabilizer bar bushings, sway bar mount bushings
- Sway bar bushing
- Sway bar bracket UK: Anti-roll bar clamp
- Sway bar
- Front subframe
How do sway bar bushings work?
The sway bar (anti-roll bar) is a spring-steel bar that runs across the car and joins the left and right suspension, through a sway bar link at each end. In between, it is held to the car at two points, and at each one a split rubber bushing wraps around the bar and a bolted bracket clamps the bushing down. In the app's MacPherson strut model each bushing sits on a pedestal on the front subframe, the steel frame that also carries the control arms and the steering rack.
When both front wheels rise together, the whole bar turns in its bushings and does no work. In a corner the outer wheel rises and the inner one drops, the links twist the bar, and its resistance keeps the body flatter. The bushings let the bar turn, keep it from sliding sideways and carry the forces the twisted bar puts into the car, all without the bar touching metal, which also keeps road noise from traveling up the bar into the cabin.
What are the symptoms of bad sway bar bushings?
- A squeak or creak over bumps. Loudest at low speed over speed bumps and driveway ramps, and on cold days, as the bar turns in rubber that has dried out. Why does my car squeak when I go over bumps?
- A clunk over bumps or as the car leans. Once the rubber has worn thin, the bar can move in its bracket and knock, a deeper sound than the rattle of a worn sway bar link. What causes a knocking noise over bumps?
- More body roll in corners. A bar that can shift in its bushings starts working late, so the car leans further before it settles into a turn.
- A loose feel on broken pavement. With the bar no longer held firmly, the front end feels less settled over uneven roads and in quick changes of direction.
- Cracked, split or squeezed-out rubber. With the car safely raised, look at each bushing where it meets the bar: deep cracks, rubber pushed out of the bracket, a gap around the bar or a polished band on the bar all show wear.
Can you drive with bad sway bar bushings?
Fix it soon
Yes, for a while. Sway bar bushings do not hold the car up or steer it, so worn ones are mostly a noise and a little extra lean in corners. Have them replaced soon all the same: a bar that moves in worn bushings knocks against its brackets and wears its links faster, and a bushing that is badly cracked or missing can fail a state safety inspection, because the federal criteria for those inspections reject cracked or missing rubber bushings.
What do worn sway bar bushings sound like?
Mostly a squeak or creak at low speed, as the bar turns in rubber that has dried out, loudest over speed bumps taken at an angle and on cold mornings. Once the rubber has worn thin or split, the bar can move in its bracket, and the squeak turns into a dull clunk over bumps and as the car leans into a turn.
The noise comes from nearer the middle of the car than the wheels, which helps tell it from a worn sway bar link at the end of the bar. With the car parked, rock it firmly side to side while a helper listens underneath: the bar turns in its bushings as the body rolls, so a dry one squeaks on cue. A polished band on the bar beside a bushing shows the bar has been turning against hardened rubber.
What does replacing sway bar bushings involve?
- Park on level ground and chock the wheels. Many bushings can be reached from underneath with the car on drive-on ramps, which keeps the suspension at its normal height so the bar is not twisted.
- Remove any splash shield under the engine that covers the bar, and look at the sway bar links while they are in view.
- Unbolt one bracket and take it off, then open the old bushing along its split and slide it off the bar.
- Clean the bar where the bushing sat. If the new bushing is meant to be greased, coat its inside with the grease that comes with it, then fit it with its split facing the same way as the old one.
- Put the bracket back on over the new bushing and bolt it down, then do the other side the same way.
- Lower the car and drive slowly over a few speed bumps to check that the noise has gone.
Tighten every nut and bolt to the torque spec in the manufacturer's service manual for your car.
One of the simpler suspension repairs, and the bushings are usually replaced on both sides at once. On some cars the exhaust or the subframe is in the way of the brackets, which makes it a shop repair.
Questions people ask
What is the difference between sway bar bushings and sway bar links?
Where they hold the bar. The two bushings clamp the middle of the sway bar to the car and let it turn; the two links join its ends to the suspension through small ball joints. Both wear and both make noise over bumps: worn links usually rattle or knock at the wheel end, and dry bushings squeak or creak nearer the middle of the car.
Do bad sway bar bushings cause vibration?
Rarely a steady vibration. Worn bushings let the bar knock and rattle on rough pavement, which you can feel through the floor, but a smooth shake that builds with speed on the highway points to a wheel out of balance or a tire fault instead.
Should sway bar bushings be greased?
Only if they are made to be. Many replacement bushings come with a packet of grease or a slippery liner, and polyurethane ones need their grease to stay quiet. Use the grease supplied, or a silicone or other rubber-safe grease, because petroleum grease makes most rubber swell and soften.
Related
Symptoms
- Why does my car squeak when I go over bumps? A squeak or creak over bumps usually comes from rubber in the suspension that has dried out or worn: the control arm bushings, the sway bar bushings or the strut mount.
- 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 is a sway bar link? A sway bar link is a short rod with a ball joint at each end that connects the sway bar to the suspension, so the bar can resist body roll in corners.
- What do control arm bushings do? Control arm bushings are the rubber mountings where a control arm pivots on the subframe.
- What is a strut mount? A strut mount is the rubber-bonded mounting that bolts the top of a MacPherson strut into the car's body and carries that corner's weight.
- 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.
The whole system
- How does a MacPherson strut work? The MacPherson strut, part by part, with an interactive diagram.
