2010-2011 Audi S4 Brake Noise: Squeal, Grinding and Pulsation Causes

By Core Brake Parts Tech Team — Circleville, OH warehouse

Most brake noise on a 2010-2011 Audi S4 comes from three places: pads worn down to their wear indicator (squeal), pads worn to the backing plate (grinding), and uneven pad deposits or overheated front rotors (pulsation). The S4 carries big 4-piston front calipers and an electromechanical rear parking brake, so the diagnosis is straightforward but the rear job needs a scan tool. Here is how to tell which problem you have and what fixes it.

How the 2010-2011 S4 Brake System Is Laid Out

The B8-generation S4 that launched for 2010 with the supercharged V6 uses vented discs at all four corners. Contemporary road tests list 13.6-inch vented front discs clamped by 4-piston calipers with the S4 logo on the cover, and 13-inch vented rear discs. The car also has a brake disc wiping function that lightly applies the pads in the wet to keep the discs clean and dry, along with ABS and electronic brake-force distribution.

At the rear, the parking brake is electromechanical: a motor on each rear caliper applies the pads instead of a cable. That matters for noise diagnosis because you cannot simply push the rear pistons back with a clamp. The rear caliper has to be put into service mode with a diagnostic tool (VCDS or an equivalent scan tool) before the pads come out, and the motor connector should be unplugged before the caliper is removed.

The pads use an electrical wear sensor, and the front axle does most of the stopping, so the front brakes are where most noise complaints start.

Squeal: What It Means and How to Diagnose It

A high-pitched squeal is the most common complaint, and it has more than one cause. Work through them in this order:

• Wear indicator contact. Many pads carry an acoustic wear indicator that squeals when the friction material gets thin. Brembo advises replacing pads at 3 to 4 mm of friction material; Power Stop places its mechanical indicators to sound at roughly 1/8 to 1/4 inch remaining. If the squeal is constant while driving and changes when you press the pedal, suspect an indicator. On the S4, the dash wear warning from the electrical sensor is another clue.
• Dry or worn hardware. Pad clips lose spring tension over time, and a pad that can vibrate in its bracket will sing. Lack of lubricant at the pad ears and backing plates is a classic cause. Replace the clips with every pad job and lubricate contact points only, never the friction surface.
• Glazed pads or rotors. Heavy heat from spirited driving or a long downhill can leave the pad and rotor faces smooth and shiny. Glazed surfaces squeal and grip less.
• Poor or skipped bedding. New pads that were never bedded in lay down an uneven transfer layer and are a common source of noise right after a brake job.
• Moisture. A brief squeak on the first few stops after rain or a car wash is surface rust coming off the discs and is normal if it clears quickly.

Grinding: Stop Driving on It

A loud metallic grind or scrape is the most urgent noise. Brembo calls it a red alert: the friction material is gone and the metal backing plate is scraping the disc. Every stop from that point cuts into the rotor face, and on discs this size that turns a pad job into a pad-and-rotor job very quickly. A lighter scraping that comes and goes can also be a stone trapped between the rotor and the dust shield, so look before you assume the worst.

To check, pull the wheel and look at the pad through the caliper window and at the rotor face. Deep circular scoring, a raised lip at the outer edge, or a bright band where metal met metal all mean the rotor needs replacing along with the pads.

Pulsation: Why the Pedal or Wheel Shakes

A pedal that pulses or a steering wheel that shakes under braking usually comes from the front rotors. Brembo lists vibration in the pedal or steering wheel as a common sign of discs that have been overheated. A very frequent mechanism is uneven pad deposits: when bedding is skipped, friction material builds up in patches, and the pad grabs differently as each patch passes. Power Stop specifically warns that skipping break-in leads to pedal pulsing, steering wheel vibration and vehicle vibration.

Before blaming the rotors, confirm the pulsation happens only under braking. A shake that is also there when you coast points to tires, wheel balance or suspension rather than brakes. Also make sure the hub face was clean when the rotors went on; rust or debris between hub and rotor creates runout that feels exactly like a bad rotor.

The Fix: Pads, Rotors and Which Parts to Buy

The table below maps each symptom to the most likely fix.

If the rotors are scored, lipped or causing pulsation, replace the front pads and rotors as a set so the new pads start on a fresh, flat surface. For the front axle we carry the Brembo OE KTX0106 front brake kit for the 2010-2011 Audi S4, which pairs high-carbon cast-iron Xtra drilled rotors with Brembo Prime ceramic pads. Brembo builds its Prime ceramic pads with a black shim to reduce noise and vibration and a low-dust, copper-free compound, which directly targets the squeal and wheel-dust complaints S4 owners have.

If you only need pads or want to compare other options, see our brake pads and brake rotors collections, and pick up fresh clips and pins from our brake hardware kits.

What to Replace at the Same Time, and How Hard the Job Is

• Wear sensors. Once the sensor has been worn through, it will not reset. Replace it whenever the warning has come on.
• Pad clips and hardware. New clips with every pad change are cheap insurance against squeal.
• Brake fluid. Check its condition and the service interval in the owner's manual while the wheels are off.

The front job is well within reach of a careful home mechanic: the caliper comes off its carrier, the carrier comes off the knuckle, and a small Torx screw locates the rotor on the hub. The carrier bolts are very tight from the factory, so use a breaker bar and a quality socket. Clean the hub face, apply anti-seize to the hub and bolt threads, lubricate the pad contact points, and torque every fastener to the value in the factory service manual. The rear job is harder only because of the electric parking brake: without a scan tool to put the calipers in service mode, do not attempt it.

Finish with a proper bedding procedure. Power Stop's published break-in for drilled and slotted rotors is five moderate to aggressive stops from 40 mph down to 10 mph without coming to a complete stop, then five stops from 35 mph to 5 mph, followed by about five minutes of easy driving to cool the brakes. Always follow the bedding instructions supplied with the parts you install.

Frequently Asked Questions

Why do my new S4 brakes squeal right after a pad change?

The usual causes are skipped bedding, reused or missing pad clips, or no lubricant on the pad ears and backing plates. Clean, lubricate the contact points, install new clips and bed the pads in again.

Can I just resurface the rotors to fix pulsation?

Only if the rotor stays above the minimum thickness marked on it after machining. On performance discs that are already worn, replacing the rotors and pads together is usually the better fix.

Do I need a scan tool for the rear brakes on a 2010-2011 S4?

Yes. The rear calipers use an electromechanical parking brake, so they must be put into service mode with a diagnostic tool before the pistons can be retracted.

Are drilled rotors noisier than plain rotors?

Not inherently. Noise comes mainly from the pad compound, the shims and hardware, and how well the pads were bedded. A ceramic pad with a quality shim, installed with new clips and bedded properly, is typically quiet on drilled rotors.

Is a brief squeak on a wet morning a problem?

No. Light surface rust forms on the discs overnight in damp weather and wipes off in the first few stops.

Sources

1. Automotive Addicts 2010 Audi S4 review - 13.6-inch front vented discs with 4-piston S4 calipers, 13-inch rear vented discs, brake disc wiping, ABS and EBD
2. FCP Euro B8 Audi S4 brake DIY - electronic parking brake needs a diagnostic tool, wear sensor connector, carrier bolts, Torx rotor screw, anti-seize and lubricant
3. Brembo pad and disc replacement guide - acoustic wear indicators, metallic grinding means friction material is gone, vibration from overheated discs, 3-4 mm pad replacement point
4. Brembo Prime ceramic pads - black shim to reduce noise and vibration, low-dust copper-free compound
5. Power Stop causes and solutions for squealing brake pads - wear indicators at 1/8-1/4 inch, pad clips, lubrication, glazing, moisture, poor break-in
6. Power Stop break-in procedure - bedding steps and pulsation from skipped break-in
7. Brembo OE KTX0106 kit details - fitment for 2010-2011 S4, Prime ceramic pads and high-carbon cast-iron rotors