CHASSIS-PARTS GLOSSARY
Bushing
Also called: bush (UK), rubber bushing, control arm bushing, suspension bush, silent block or silentbloc (common in European and Russian catalogues). Polyurethane versions are often sold as poly bushes.
What it is
A bushing (bush) is a rubber or polyurethane sleeve, usually bonded between an inner and an outer metal tube, that mounts a suspension or steering arm to the body or frame while letting it pivot. It lets the arm move, absorbs vibration and road noise, and gives a small, controlled amount of compliance. Bushings are fitted to control arms, stabilizer bars, trailing arms, leaf springs, subframes and some idler arms. As the rubber ages, cracks or separates from its sleeve, the arm starts to move in ways the suspension geometry did not intend.
How it works
A pivot without metal-to-metal contact
In a bonded bushing the rubber twists as the arm moves up and down. There are no sliding surfaces, so it needs no lubrication and makes no noise when new.
Isolation
The rubber absorbs vibration and road noise before they reach the body, which is why bushings strongly affect ride comfort.
Controlled compliance
Engineers tune the rubber's stiffness, and voids moulded into it make a bushing softer in one direction and stiffer in another, for example soft fore-and-aft for comfort and stiff sideways for precise handling.
Construction
A typical bushing is a rubber body vulcanised (bonded) to an inner steel sleeve and an outer steel shell. The outer shell is pressed into the eye of the arm, and the mounting bolt clamps the inner sleeve. Hydraulic bushings add fluid-filled chambers for extra damping. Polyurethane bushings are harder and usually not bonded, so they rotate on a greased sleeve.
Common failure symptoms
- Clunk over bumps or when braking
- A worn bushing lets the arm shift until metal parts knock.
- Vague steering or wandering
- The arm moves under load, changing the alignment while driving.
- Uneven tyre wear
- Toe and camber change as the worn rubber deflects.
- Visible cracks or separation
- Cracked rubber, or rubber torn away from its sleeve, is visible on inspection.
- Vibration under braking
- Worn control-arm bushings let the wheel move fore-and-aft when the brakes are applied.
Frequently asked
What is the difference between a bushing and a ball joint?
A bushing is a rubber pivot that twists and absorbs vibration; a ball joint is a metal ball and socket that rotates freely in several directions. A control arm usually has bushings at the body and a ball joint at the wheel end.
Can I replace just the bushing instead of the whole control arm?
Often yes, with a press and the right tools. On many vehicles a complete control arm with new bushings and ball joint is quicker to fit and renews every wear point at once.
Are polyurethane bushings better than rubber?
They are stiffer and resist oil and ageing, which sharpens handling, but they pass more noise and vibration and need lubrication. OE-type rubber bushings keep the original ride and noise level.
Why should bushing bolts be tightened at ride height?
The rubber is bonded to the sleeve, so the position at tightening becomes its rest position. Tightening with the wheels hanging pre-twists the rubber at normal ride height and shortens its life.
What is a silent block?
Silent block is another name for a bonded rubber bushing, common in European and Russian parts catalogues.
Do I need a wheel alignment after replacing bushings?
Usually yes for control-arm bushings, because they locate the arm that sets camber, caster or toe. Stabilizer-bar bushings do not change the alignment.
Example OE numbers
- 48069-20360 Toyota
- 51350-S04-A10 Honda
- 545008Z400 Nissan
- 4013A209 Mitsubishi
- 48630-60010 Toyota
- 48068-02330 Toyota
External references
Independent technical sources (in English) for further reading. SLOOPZONE is not affiliated with these publishers.
- Bushing (isolator) Wikipedia
- Control arm Wikipedia
- MOT inspection manual, 5. Axles, wheels, tyres and suspension GOV.UK