In short. A squeak is the brake vibrating: the pad rubs on the disc (the rotor, in the US) and the slightest change in contact makes the assembly sing at a high pitch. Most of the time it is harmless: moisture or a film of rust on the disc on the first stop of the day, dust between pad and disc, new pads not yet bedded in, or braking so gently that the surfaces never get cleaned. Three cases call for action: a squeal that comes back on every stop (often the wear indicator touching the disc), a metallic grinding (the pad is used up: stop driving and have the brakes checked before you go back on the road), and a noise that started right after a repair (the fitting needs looking at).
A squeak is a vibration, not usually a faulty part
Brembo puts it plainly in its workshop advice on noise: the cause is often not the new part but "the poor wear condition of the other braking system components" (Brembo). An Audi bulletin of April 2023, written for every Audi model from 2000 to 2024, starts from the same point: when the pad thickness is fine, brake noises are often down to contamination with brake dust, rust, road grit or other outside influences (Audi TSB 2069904/1).
So new pads at the first squeak may not stop it. Start with when it happens.
High-pitched or rhythmic? A calculation that sorts the two
A Bentley bulletin on identifying brake noise shows, as its example, a squeal whose peak sits at 2,000 Hz (Bentley TSB 2052785/3). Compare that with how fast the wheel turns. For a 225/45 R17 tyre, taken only as an example:
| Working | Result | |
|---|---|---|
| Sidewall height | 225 mm × 0.45 | 101.25 mm |
| Overall diameter | 17 × 25.4 + 2 × 101.25 | 634.3 mm |
| Circumference | π × 0.6343 m | 1.993 m |
| Wheel turns per second at 5 mph (2.24 m/s) | 2.24 ÷ 1.993 | 1.12 |
| at 10 mph | 4.47 ÷ 1.993 | 2.24 |
| at 30 mph | 13.41 ÷ 1.993 | 6.73 |
| Vibrations per wheel turn for a 2,000 Hz squeal at 10 mph | 2,000 ÷ 2.24 | about 890 |
Our reading: a steady high-pitched squeal has nothing to do with the wheel's rotation; it is the pad, caliper and disc vibrating together. A noise that beats in time with the wheel, faster as you speed up (one to seven beats a second in the example), comes from something turning with it: a disc with uneven thickness, a stone, a dust shield touching the disc, or a wheel bearing. The tyre size calculator gives the circumference of your own tyre.
When it squeaks: what it usually means and what to do
Each row points to a brake or car maker's document; "our reading" marks what none of the documents we read describes.
| When it squeaks | What it usually means | Source | What to do |
|---|---|---|---|
| First stops of the morning, cold and damp, then nothing | Moisture or a film of rust on the disc | Audi Q5 bulletin: first application, cold brakes, below 20 mph, below 40°F, high humidity | Nothing, if it fades within a few stops and the car brakes straight |
| Gentle stops at low speed | Surfaces dirty or glazed, which light braking never cleans | Audi 2023: noise more likely with short trips and very light braking | Brake firmly now and then when traffic allows; if it stays, have the brakes cleaned |
| After new pads or discs | Not bedded in yet, or a fitting fault (shims, direction, grease) | Bentley: not properly bedded in; TRW and Bosch: direction of fitting | Finish bedding in; if it lasts, have the fitting checked |
| A sharp squeal on every stop, wet or dry | Audible wear indicator touching the disc | Hella; MOT manual 1.1.13 | Have the pads checked and replaced without delay (worn to the indicator is a major MOT defect) |
| Grinding, metallic growl | Lining used up, metal on metal | Audi 2013 and Bentley: discs or pads close to the wear limit | Stop driving; have it checked before you go back on the road |
| In reverse, often on the first stop backwards | Pad shifting in its bracket when the direction changes | Our reading: no document we read describes it | Usually harmless; have it looked at if it is new, loud or comes with a clunk |
| While driving without braking, or when turning | Something rubbing all the time: bent dust shield, sticking caliper or pad, stone | Bosch: seized pistons and stuck pads cause rubbing and overheating | Have it checked; a wheel much hotter than the others after a drive is a reason to stop (our reading) |
| After cleaning the wheels | Wheel or tyre cleaner sprayed on the disc | Audi 2013 and Bentley: chemical contamination of the disc | Rinse, brake gently a few times; have it checked if it stays |
| With a shudder in the pedal or steering wheel | Disc run-out or thickness variation | Bosch: run-out measured with a dial gauge | Have the discs and hub measured |
Sources: Audi Q5 TSB 2042182/2, Audi TSB 2069904/1, Audi TSB 2034181/1, Bentley TSB 2052785/3, Hella, Bosch, TRW.
Morning squeal: moisture and surface rust
After a damp night, rain or a car wash, the disc grows a thin film of oxide. Audi's Q5 bulletin describes the case precisely: a squeal on the first application in the morning, with cold brakes, below 20 mph (32 km/h), below 40°F (4.4°C) and in high humidity. Audi and Bentley both list rust that forms when a car has stood for a long time, and "pad marks": pad material that transfers to the disc where the pad rested, when the car stood in a wet or snowy place.
Bosch links deeper corrosion to road salt, cleaning products and too little use of the brakes, and then replaces discs and pads: that is a car that has barely moved, not one wet night. When rust or a shudder stays, see our guide to warped or rusty brake rotors.
Squeaking when stopping slowly
The 2023 Audi bulletin explains why light braking is the noisy kind: noise is more likely with low mileage, short trips and very light brake applications, which do not clean the brake enough or build up optimum friction on the faces. It adds that glazed pads (a hardened, shiny surface) also make noise, a sign of strong or excessive heat. Its remedy is to bed the brakes in properly and to brake them clean at regular intervals, with a driving style suited to the traffic. A workshop can rework a glazed or very dirty pad surface with abrasive paper and brake cleaner and bed it in again; Audi says it is not necessary to replace parts.
Squeaking after new pads
It is one of the most common ways people phrase the question. The makers describe four causes.
1. The pads are not bedded in. Bentley lists new pads or discs "not properly bedded in" among its eight most common causes. Brembo asks fitters to recommend bedding in over about 300 km (about 186 miles), avoiding abrupt braking. Audi's Q5 bulletin describes, for its replacement pads, ten slow-downs from about 35 to 10 mph with medium pedal pressure, then about five minutes of driving without braking to cool them, and says not to use ABS stops to bed brakes in. The leaflet in your pad box is the one to follow; procedures differ between makers.
2. Shims missing or reused. Shims are thin plates on the back of the pad that damp vibration. Brembo says to fit them correctly and not to reuse the old one; Audi says not to transfer the shims from the old pads to the new. Brembo also has the caliper springs checked and replaced if worn.
3. Pads fitted the wrong way round. TRW describes pads chamfered on one side to reduce noise: fitted other than as shown, "noise will occur", and it says it will print rotation arrows on the backing plate. For another set, it places the chamfers against the disc's forward rotation, and says a pad with a spring goes on the piston side, or it causes noise, faster wear and possibly reduced braking. Bosch reminds fitters to check the direction of directional pads.
4. The wrong grease, or grease in the wrong place. See the next section, where the makers disagree most.
Brembo also has the fitter check disc wear, clean the disc-to-hub faces, and measure the run-out of the fitted disc (no more than 0.10 mm, and 0.050 mm for the hub alone): a worn or grooved disc makes new pads squeal.
Grease: four makers, four instructions
We compared the instructions in four documents read on 16 October 2026:
| Document | Where to grease | What is forbidden |
|---|---|---|
| Bosch repair brochure | Pad ears (where the pad slides in its seat), with brake grease | Any lubricant containing copper; any lubricant on the adhesive layer on the back of a pad |
| Brembo, noises and vibrations | Contact faces between caliper bracket and pads, with anti-noise grease; sliding parts with a grease that does not attack rubber | Reusing the old shim |
| TRW, service information | The red shim on the back of some pads, with the supplied tube, shared between all four pads | Forcing a pad into the caliper |
| Audi, Q5 2013-2017 bulletin (pads bonded to the pistons) | Nowhere | Any lubricant on the pads or calipers; pistons cleaned and dried for the bond |
Bosch gives the mechanism: copper grease can cause resonant vibration or stop the pads returning freely to the released position, and so cause squeal (our translation). The one rule they all share: never grease or oil on the friction lining or the disc face. The MOT treats a pad or disc contaminated with oil or grease as a major defect.
In practice, follow the pad maker's leaflet and the car maker's manual: a general tip to "put paste on the back of the pads" is wrong for a pad with an adhesive back.
The squeal that comes back every stop: the wear indicator
Many pads carry a small steel tab on the backing plate. Hella describes this acoustic indicator as "purely mechanical": at the wear limit, usually 2 mm for disc brake pads, the disc touches the tab and it squeals (Hella). The MOT manual describes the same thing: some pads have metal wear indicators so that, when the pads are excessively worn, the indicator touches the disc and makes a squealing sound (MOT manual, 1.1.13).
Our reading: it comes back on every stop, wet or dry, often from one wheel, and does not fade like the morning film of rust. Other cars use an electrical sensor and a warning light instead; the US standard allows either an acoustic or optical device, or a way to check wear by looking. How thick a pad should be, and how wear sensors work, is in our guide to when to replace brake pads.
If the squeal turns into a deep metallic grinding, the lining is gone and the backing plate is on the disc. Braking gets worse and the disc is being cut: stop driving and have the brakes checked before you go back on the road.
Squeaking in reverse, when turning, or with the brakes off
In reverse. None of the documents we read describes this case, so this is our reading, not a maker's: a pad sits in its bracket with a little clearance. When you brake going forward, the disc drags it against one side; when you brake backwards, it shifts to the other side, and that first contact can tick or squeak. It tends to happen on the first stop in reverse, at walking pace. If it is new, loud, or comes with a clunk, the clips, shims or guides may be worn or missing: have it looked at.
With the brakes off, or when turning. A noise with your foot off the pedal is not braking friction. Bosch names seized calipers or pistons that keep the pad on the disc: rubbing, overheating, uneven wear, a car that pulls to one side. A dust shield (the thin plate behind the disc) can be bent during a wheel change or by an obstacle and touch the disc; our reading is that this gives a rhythmic scrape in time with the wheel. A worn wheel bearing makes a noise that changes with speed and cornering (wheel bearing noise explains how to tell), and a vibration that follows speed may be a balance problem rather than the brakes.
What inspections check, country by country
No inspection we read fails a car for noise. They look at what noise may be a sign of: pad thickness, contamination, fitting. Here is what we read, with the thresholds converted by us (1 inch = 25.4 mm):
| Where | Text | Pads | Category or rule |
|---|---|---|---|
| Great Britain | MOT inspection manual, 1.1.13 (updated 14 October 2026) | Worn down to wear indicator | Major |
| Worn below 1.5 mm | Dangerous | ||
| Contaminated with oil, grease etc. | Major | ||
| Missing or incorrectly mounted | Dangerous | ||
| United States (example: Pennsylvania) | 67 Pa. Code § 175.80(e)(7), amended 2013 | Bonded lining under 2/32 in (1.59 mm); riveted under 1/32 in (0.79 mm) above the rivet head | Reject |
| Disc scored deeper than 0.015 in (0.38 mm); lining contaminated with oil or grease | Reject | ||
| Canada (Ontario) | MTO Passenger / Light-Duty Vehicle Inspection Standard, section 3 | Under the maker's figure; if none, bonded under 1.6 mm, inner and outer pads differing by more than 3.2 mm | Reject |
| Pad contaminated or installed incorrectly; "rust-jacking" (lining lifting from its backing through rust) | Reject |
Sources: MOT manual, 67 Pa. Code § 175.80, Ontario standard.
Two points behind the table. The MOT manual adds that an illuminated brake wear warning light is not in itself a reason for failure, and that a disc must be significantly worn before it is rejected. In the US, periodic inspection, where it exists, is set by each state: Pennsylvania is the one code we read, and other states may differ.
The design rules sit upstream. The US federal standard for light vehicle brakes, FMVSS No. 135, requires the wear of the service brakes to be shown either by "acoustic or optical devices" warning the driver, or by a way of checking lining wear visually (49 CFR 571.135, S5.1.2). In Australia, ADR 31/04 asks that pad wear can be assessed easily from outside or under the car without removing the wheels, or by a sensing device per wheel that warns the driver (ADR 31/04, 5.2.11.2). Roadworthy inspections in Australia are run by each state; we could not read a state manual for this guide, so check with your state's transport authority.
How the thresholds compare: Hella gives the wear limit at which its acoustic indicator sounds as "usually" 2 mm, and Bosch's own workshop checklist puts the wear limit at 4 mm without the backing plate. Both are above the numeric floors in the table (1.5 mm at the MOT, 1.59 mm in Pennsylvania, 1.6 mm in Ontario). But do not read the squeal as an early warning with time to spare: at the MOT, a pad worn down to its wear indicator is already a major defect. Our reading: once the indicator squeals, the pads are due now, not at the next service.
Before you look for yourself
If you take a wheel off to see the pads: park on level ground, lift the car, then rest it on axle stands; never work under a car held only by the jack. The steps are in our guide to changing a wheel safely, and the nuts or bolts go back on at the car maker's torque, in a crosswise order, as explained in wheel nut torque; Brembo asks for the right sequence and a torque wrench. To clean wheels without spraying product on the discs, a cause of noise named by Audi and Bentley, see wheel finishes and how to care for them.
No spray lubricant or penetrating oil on a brake: anything that lubricates where the brake must grip quietens the noise by taking braking away (our reading).
Frequently asked questions
Is it dangerous to drive with squeaking brakes?
Not always. A morning squeak that fades after a few stops, with the car braking straight, is moisture. A squeal on every stop warns that the pads are at their wear limit: have them replaced without delay. A metallic grinding, a pedal that sinks, a car that pulls, or a very hot wheel: have it checked before you go back on the road.
Why do my brakes squeak when I stop slowly?
Light pressure lets the pad vibrate, and gentle braking never cleans the faces. Audi's 2023 bulletin ties these noises to short trips and very light braking, and advises braking the brakes clean at regular intervals when traffic allows.
Why do my brakes squeak after new pads?
Bedding in not finished, shims missing or reused, pads fitted the wrong way round, the wrong grease, or a worn disc kept with new pads. Brembo gives about 300 km (186 miles) of bedding in without abrupt braking; Audi says the distance depends heavily on how the car is driven. If the noise lasts, have the fitting checked.
Why do my brakes squeak in reverse?
No document we read covers this, so this is our reading: the pad shifts in its bracket when the direction changes, and the first contact can squeak. It is usually harmless; have it looked at if it is new, loud or comes with a clunk.
My brakes squeak in the morning, then stop. Should I worry?
No, if it fades within a few stops. That is the case Audi describes: first application, cold brakes, low speed, cold and humid weather. A car that has stood for weeks can keep marks on the disc (Bentley); if the noise stays, have it checked.
Should I put grease on brake pads?
Never on the lining or the disc. Elsewhere it depends on the pad and the car: Bosch greases the pad ears with copper-free grease, TRW supplies a tube for some shims, Audi forbids any lubricant on bonded pads. Follow the leaflet.
Will a lubricant spray stop squeaky brakes?
Do not spray anything on a brake. A pad or disc contaminated with oil or grease is a major defect at the MOT and a reject in Pennsylvania and Ontario, because it reduces braking.
Wheels and brakes
A wheel is also chosen around the brakes it covers: the caliper has to clear the spokes and the barrel, which our caliper clearance guide explains. Onyx Forged does not recommend a size or an offset; the Onyx Forged design office sends the dimensions of a set in writing before anything is made, and the wheels are designed to JWL/VIA standards. The models are in the catalogue.
Sources
- Audi of America, TSB 2069904/1, Noises when braking (18 April 2023); TSB 2034181/1, Brake noise analysis and handling (7 August 2013); TSB 2042182/2, Squeal from front brakes (4 April 2016), archived by NHTSA.
- Bentley, TSB 2052785/3, Brake noise identification (17 May 2019), archived by NHTSA.
- Brembo, Noises and vibrations.
- Hella Tech World, Brake pad wear indicator.
- Bosch, disc brake diagnosis and repair brochure (10/2019, in French; our translation).
- TRW (ZF Aftermarket), service information on brake pad installation.
- GOV.UK, MOT inspection manual, section 1: brakes (updated 14 October 2026).
- 67 Pa. Code § 175.80, Inspection procedure (Pennsylvania).
- Ontario Ministry of Transportation, Passenger / Light-Duty Vehicle Inspection Standard.
- 49 CFR § 571.135, FMVSS No. 135, Light vehicle brake systems.
- Australian Design Rule 31/04, Brake Systems for Passenger Cars (2017).
All pages were read on 16 October 2026.
The Onyx Forged design office.