Audi S4 Brake Upgrade Options

By Core Brake Parts Tech Team — Circleville, OH warehouse

An Audi S4 brake upgrade comes down to three decisions: rotor style, pad compound, and whether the hardware around them is fresh. On most S4 generations you do not need a bigger caliper to cure squeal, fade or a wooden pedal - you need the right friction pair on a clean, free-moving caliper. Here are the options that actually fit an S4 and what each one changes.

Identify Your S4 Before You Buy Anything

The S4 name covers very different cars. The B5, B6 and B7 cars use one family of rotor sizing, the supercharged 3.0L cars from 2008 to 2011 use another, and the 2018-and-newer turbocharged 3.0L is different again. Ordering by year alone is how people end up with a rotor that will not clear the caliper.

Audi also built the same model year with more than one front brake package, and the car is coded for it. An Audi technical service bulletin on front brake squeal (TSB 46 14 89 2027636/8, July 21, 2014) is built around option code PR-1LJ and separates cars by disc thickness: PR-1LJ cars built before June 20, 2011 have 29.5 mm front discs, PR-1LJ cars built after that date have 30 mm, and PR-1ZT cars are also 30 mm. It covers 2010-2011 S4s with PR-1LJ and 2012 S4s up to VIN 007700. Check the option code sticker rather than guessing from the model year.

That same bulletin publishes the factory wear limits: the front brake disc wear limit is 28 mm, and the front brake pad wear limit, measured with the backing plate and dampening sheet included, is 10 mm. Measure what you have before you spend anything - a disc already at the limit is not a candidate for resurfacing.

Rotor Upgrade Paths for the S4

There are three honest rotor upgrades for this car, and they solve different problems.

Dimpled and slotted discs. EBC's GD Sport range uses wide aperture slots plus dimples that stop short of going all the way through the disc face. EBC says it invented the dimple-drilled design in the 1990s precisely because fully through-drilled holes have been shown to promote cracking, while dimples still give the pad somewhere to vent gas and dust. The blanks are R90-approved grey iron, machined in the UK and finished with a corrosion-resistant coating, and EBC positions the range for fast street cars. The GD1421 front set for the 2004-2008 4.2L S4 and the GD1571 front set for the 2008-2011 supercharged 3.0 are the two most common fitments, with the GD1572 rear set matching the later car.

Fine multi-slot discs. EBC's USR range trades the wide slot for a narrower, progressively angled multi-slot pattern. EBC's reasoning is noise: the finer pattern still scrubs gas and debris off the pad face and keeps pad wear flat and parallel instead of letting ridges build, but it makes far less air noise under heavy braking. EBC calls this its quiet street range and recommends pairing it with its higher-friction compounds. If your S4 is mostly a road car, the USR1571 front pair and USR1572 rear pair are the version of the same idea with the volume turned down.

Two-piece floating discs. This one changes how the car drives, not just how the brakes behave. A two-piece disc bolts an iron friction ring to an aluminum center hat through drive pins so the ring can grow with heat instead of fighting the hat. GiroDisc machines its hats from 6061-T6 aircraft-specification aluminum and its own cadmium-plated high-strength alloy steel drive pins, secured with grade 12 cap screws and anti-noise spring clips; the assembly keeps both axial and radial float, which lets the ring self-center between the pads. The rings are cast in high-carbon iron with curved vanes that act as a centrifugal pump, drawing air through the hub. Brembo, which builds the same style of disc, states up to 30 percent weight reduction versus an integral disc of the same size, notes that the saving is unsprung weight, and says letting the braking surface expand elastically is what prevents permanent deformation and cracking.

The other advantage is consumables: when the iron is worn you replace the ring and keep the hat. Our GiroDisc D2-143 slotted 300 mm rear replacement rings for 1997-2009 B5, B6 and B7 S4s are exactly that.

Pad Compound Is Where the Bite Comes From

A rotor manages heat and keeps the pad face clean. The pad decides how hard the car stops. EBC's Greenstuff 2000 compound carries a nominal friction coefficient of 0.55, is described by EBC as a medium-to-low dust material, and is ECE R90 approved for road use. EBC claims a nominal 10 to 15 percent braking improvement and ships the pads with a red brake-in coating that seats them quickly. EBC is straight about the limits: Greenstuff 2000 is not recommended for regular track use, and it points buyers to faster street and race compounds for that. For a B9 car, the Greenstuff 2000 DP22277 front set for 2018-and-newer 3.0L turbo S4s is the direct fit. Browse the full range in brake pads if you want a different compound for the same car.

On bedding, EBC treats its street pads as largely self-bedding thanks to that coating, with nothing further required after roughly the first 100 miles of normal driving. If you drive hard, expect some odor or smoke past about 300 miles as surface volatiles burn off at rotor temperatures in the 400 to 500 degree Celsius range - that is the final high-temperature bedding, not a fault.

If Your S4 Squeals, Read the Bulletin First

Front brake squeal on the B8 S4 is a documented factory issue, not a sign you bought bad parts. Audi's bulletin describes brakes that squeak or squeal under light to moderate pedal force on affected cars built before September 3, 2012. The production fixes are telling: from June 20, 2011 the factory fitted discs, brake carriers and pads with noise insulation, and from September 3, 2012 it applied anti-seize lubricant to the caliper guide pins on the line. The dealer repair was parts kit 8K0698998 - brake pads with wear indicator, two front discs, two brake carriers, four hexagonal collar bolts and two hexagonal countersunk screws.

Two lessons for anyone upgrading. The factory answer to squeal was a matched pad, disc and carrier set with noise insulation, so replace pads and rotors together rather than putting new pads on glazed discs. And dry or seized guide pins are a real cause on this car, which is why the hardware step below is not optional.

What to Replace at the Same Time

• Caliper hardware and guide pins. New abutment clips, fresh boots and properly lubricated pins. Audi added anti-seize to the pins in production for a reason. A set from our brake hardware kits is the cheapest part of the job and does the most for noise.
• Pad wear sensors. Audi's front pad set for these cars includes a wear indicator. Reusing a triggered sensor leaves a dash light you cannot clear.
• Brake fluid. Flush it, using the DOT specification printed on your reservoir cap and in the owner literature for your model year. Heat-cycled fluid is the usual cause of a pedal that goes long after two hard stops.
• The opposite axle. Fitting a higher-friction front pad, plan the rear at the same time so the balance does not change mid-corner. Full options are in brake rotors.

How Hard Is This Job

A front pad and rotor change on an S4 is a normal driveway job with hand tools, a torque wrench and a caliper piston tool: wheel off, caliper off its carrier, carrier bolts out, rotor retaining screw out, clean the hub face, reassemble. Torque every fastener to the value in the factory service manual for your model year - hub face cleanliness and correct carrier bolt torque are what keep runout and vibration away.

Two complications. If your S4 has an electric parking brake switch rather than a lever, the rear calipers must be put into service mode with a scan tool before the pistons will retract; do not force them. And follow the manufacturer's bedding procedure on new discs - GiroDisc states that any time different friction material or a different disc is introduced, a bedding procedure should be carried out, and it advises against pairing drilled discs with high-friction race pads because of thermal cracking risk.

Frequently Asked Questions

Do I need a big brake kit for my S4?

Most owners do not. If the complaint is squeal, dust, shudder under braking, or fade after a few hard stops, a matched pad and rotor set plus new hardware and fresh fluid solves it. A big brake kit is for repeated track sessions where you have already run out of pad compound.

Are slotted rotors better than drilled for an S4?

For a street car, slotted or dimpled is the safer choice. EBC's stated position is that through-drilled holes have been shown to promote cracking, which is why its GD range dimples the face instead of drilling through it. Slots and dimples give you the pad-venting benefit without a hole that concentrates stress.

Will performance rotors make my brakes noisier?

A wide-slot rotor can add some air noise under heavy braking. That is the specific reason EBC offers the finer USR pattern, which it describes as its quiet street range. If noise is your priority, pick the fine multi-slot version and fit new caliper hardware at the same time.

How do I know if my front discs are still usable?

Measure them. Audi's bulletin lists a 28 mm front disc wear limit and a 10 mm front pad wear limit including the backing plate and dampening sheet for the covered S4 and S5 models. If a disc is at or below the limit, replace it rather than resurfacing it.

Can I keep my two-piece hats and buy only new rings?

Yes, that is the design intent. GiroDisc sells replacement rings that bolt to the hat you already own, which is why a two-piece disc gets cheaper to own the longer you keep the car.

Sources

1. Audi of America Technical Service Bulletin 46 14 89 2027636/8 (NHTSA) - affected S4 years, PR code disc thicknesses, wear limits, parts kit 8K0698998
2. EBC Brakes - GD Sport Rotors - wide aperture slots, dimple versus through drilling, R90 iron blanks
3. EBC Brakes - USR Slotted Rotors - fine multi-slot pattern, quiet street positioning, flat pad wear
4. EBC Brakes - Greenstuff Brake Pads - 0.55 friction coefficient, ECE R90, brake-in coating, 10-15 percent claim
5. EBC Brakes - Bedding In - self-bedding inside 100 miles, burn-off past 300 miles at 400-500 C
6. GiroDisc Technical Information - 6061-T6 hats, cadmium-plated drive pins, float, replacement rings, bedding
7. Brembo - Floating Disc - 30 percent weight reduction, unsprung weight, elastic thermal expansion