2018-2019 Audi S5 Brake Noise: Squeal, Grinding and Pulsation Causes

By Core Brake Parts Tech Team — Circleville, OH warehouse

Most brake noise on a 2018-2019 Audi S5 comes from one of three things: pads worn down to their wear indicator (a high-pitched squeal), metal-to-metal contact or trapped debris (grinding), or uneven rotor thickness (a pulsing pedal or shaking wheel under braking). The fix is usually pads, rotors, or both, plus fresh hardware and a proper bed-in. The one S5-specific catch is the rear axle: its electromechanical parking brake has to be put into service mode with a scan tool before the rear pistons can be pushed back.

How the Brakes Work on the 2018-2019 S5

The B9-generation S5 (Coupe, Cabriolet and Sportback) pairs a 354-horsepower turbocharged 3.0-liter V6 with a front brake setup that is noticeably bigger than the A5's. Up front it uses six-piston fixed calipers, painted red when the car has the S sport package, clamping larger-diameter vented rotors than the A5 gets. A fixed caliper does not slide on pins the way a single-piston floating caliper does; the pistons on both sides push the pads against the rotor, and the pads ride in the caliper body held by clips and retaining hardware.

At the rear, the S5 uses disc brakes with an electromechanical parking brake (EPB) instead of a cable and lever. Each rear caliper carries a small electric motor that screws a spindle against the piston to hold the car when parked. That matters for any rear brake job, and we cover it below.

Squeal: What It Means and How to Diagnose It

A squeal is the most common complaint, and it is not always a sign of worn pads. Sort it by when it happens:

• Constant high-pitched squeal while braking, getting worse over weeks: the pads are likely near the end of their life. Mechanical wear indicators are designed to contact the rotor when roughly 1/8 to 1/4 inch of friction material remains. Pull a wheel and look at the pad thickness through the caliper.
• Squeak only on the first few stops of the morning: usually moisture and a thin layer of surface rust on the rotors. It should fade once the brakes dry out and the rust is wiped off by the pads.
• Squeal right after a brake job: most often missing or reused pad clips, no lubricant on the pad contact points, or pads that were never bedded in.
• Squeal after hard driving: heat can glaze the pads and rotors, leaving smooth, shiny surfaces that grip less and sing more.

On the six-piston front calipers, check that the anti-rattle spring and pad retaining hardware are intact and tight. Loose or fatigued clips let the pads vibrate in the caliper, and that vibration is what you hear.

Grinding: Stop Driving and Inspect

Grinding is a different category. A metal-on-metal grind almost always means one of these:

• Pads worn through to the steel backing plate. The backing plate is now cutting the rotor. Every stop does more damage, and stopping distance suffers.
• A stone or piece of debris trapped between the rotor and the dust shield, which produces a scraping sound that may happen even when you are not braking.
• A heavy rust lip on the outer edge of the rotor catching the pad edge, common on cars that sit or live where roads are salted.

If you hear grinding, get the wheels off and look before driving further. If the rotor faces show deep grooves, score marks or rough spots, the rotors are coming off along with the pads. A backing plate that has dug into the rotor leaves a groove that new pads cannot seat against.

Pulsation: Disc Thickness Variation, Not Just Warping

A pedal that pulses, or a steering wheel that shakes when you brake from highway speed, points to the front rotors. The usual cause is disc thickness variation (DTV): the rotor becomes slightly thicker in some spots than others, so the pads are pushed back and forth as it turns, and you feel that through the pedal. A related problem is lateral runout, where the rotor is the same thickness all the way around but wobbles side to side.

DTV typically builds from uneven clamping force, rust and dirt left on the hub face when the rotor was installed, unevenly torqued lug bolts, and uneven friction deposits on the rotor faces from pads that were not bedded. Here is how the checks break down:

Take micrometer readings starting about a quarter inch in from the rotor's outer edge. If the rotors are past their minimum thickness or show DTV, replace them. New brake rotors for your S5 paired with new pads are the reliable fix.

The Fix and Which Parts to Use

For squeal from worn pads, replace the pads on both sides of the axle. For grinding or pulsation, replace pads and rotors together; new pads on a worn or grooved rotor will not seat evenly and the noise often returns. Browse brake pads and ceramic brake pads for daily-driven cars.

For drivers who want more bite, we carry the Hawk Performance HPS 5.0 rear brake pads (HB866B.652) for the 2018-2019 S5. Hawk describes HPS 5.0 as a Ferro-Carbon street compound with an optimal range of 100 to 550 degrees F, a smooth, predictable feel and good rotor and pad wear life. Like every Hawk compound, it is made for iron rotors, not carbon-ceramic. Hawk lists this pad for several Audi models and notes caliper-specific fitments, so confirm your rear caliper before ordering.

Whatever pad you choose, replace the pad clips and retaining hardware at the same time. A brake hardware kit is inexpensive insurance against the post-brake-job squeal.

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

• Hardware: new clips, springs and retaining pins. Lubricate the pad contact points and backing plate ears with brake lubricant, never the friction surfaces.
• Rotors: whenever they are grooved, below minimum thickness, or show DTV.
• Hub face: clean rust and scale off the hub before installing a rotor to prevent runout.
• Lug bolts: tighten in a star pattern to the torque value in the factory service manual; uneven torque can distort the rotor.

The front job on the fixed six-piston calipers is straightforward for a home mechanic: the pads come out of the caliper once the retaining hardware is removed, and the pistons are pushed back to make room for the thicker new pads.

The rear is where people get into trouble. Because of the electromechanical parking brake, the rear pistons cannot simply be pressed back. The EPB must be opened into service mode with a scan tool that supports the VW-Audi parking brake routine. Ross-Tech's procedure notes that the EPB module is very sensitive to low voltage, so connect a battery charger for the whole job, and the parking brake must be off before starting. After the new pads are in, the calipers are closed with the same routine and a function test cycles the calipers to remove the pad-to-rotor gap. Then check for fault codes.

Finish every brake job with a proper bed-in, following the pad maker's procedure. It lays down an even transfer layer on the rotor, which is your best defense against both squeal and future pulsation.

Frequently Asked Questions

Why do my S5 brakes squeak in the morning and then stop?

Overnight moisture forms a light layer of surface rust on the rotors. The first few stops wipe it off, and the noise goes away once the brakes dry. It is normal and does not need a repair.

Can I replace the rear brake pads on a 2018-2019 S5 without a scan tool?

You should not. The rear calipers have electric parking brake motors, and the pistons need to be retracted with a scan tool's parking brake service routine before new pads will fit. Forcing the pistons back can damage the caliper motors.

Is a pulsing brake pedal caused by warped rotors?

Usually the cause is disc thickness variation, where the rotor wears unevenly, rather than a truly bent rotor. A micrometer check at several points around the rotor will confirm it. Replacing the rotors and pads together is the fix.

Should I replace rotors every time I replace pads?

Not always. If the rotors are above minimum thickness, smooth, and show no DTV or heat spots, new pads alone can work. If there is grinding, grooving or pulsation, replace both.

Will performance pads make my S5 louder?

Performance compounds can be noisier than a standard ceramic pad, especially when cold. Good hardware, correct lubrication and a full bed-in keep noise to a minimum.

Sources

1. Autoweb: 2018 Audi S5 Sportback Road Test and Review - 354 hp 3.0-liter turbo V6, six-piston front calipers, larger front rotors than the A5
2. Ross-Tech Wiki: Working on the Electro-Mechanical Parking Brake - A5/S5 EPB service mode, low-voltage warning, close and function test
3. Power Stop: Pulsing brake pedal and disc thickness variation - DTV causes, micrometer checks, 0.001 and 0.006 inch limits
4. Power Stop: Causes and solutions for squealing brake pads - wear indicator at 1/8 to 1/4 inch, clips, lubrication, moisture, glazing
5. Power Stop: Signs of bad rotors - grooves, scoring, blue heat tint, minimum thickness
6. Hawk Performance: HPS 5.0 compound - Ferro-Carbon compound, 100-550 F optimal range, iron rotors only
7. Hawk Performance: HB866B.652 - rear pad fitment across Audi models including the S5