Brakes



General Questions

My BRAKES aren't working. They don't stop well enough anymore.

You may need to re-bed your pads. That's usually a good first step in any brake diagnosis, as it surprisingly fixes many problems.

My brakes shudder a lot when I use them. Are my rotors warped?

It might just be uneven pad transfer. Again, try re-bedding the pads. If you want more info on the subject, check this writeup by Stoptech.

How do I bed my pads, and why do I need to do it?

Stoptech has a nice discussion about it here.

What are the best pads?

For what type of use? Street or track? No single pad is going to work well on the street and track. What's quiet on the street and works when cold won't hold up to increased heat on the track. Track pads are extremely noisy and abrasive on the street, but once they warm up, they stop very well. Plan to have a set of street pads for the street, and a set of track pads for the track.

Where can I read more about brake technology?

This is a good start.

What is brake bias?

Stoptech has a nice writeup on the subject.

What are the various biases of my brake options?

ECS created a nice chart here.

Why are there so many different choices of brake fluid?

Every brake system is designed to work best with a specific kind of fluid. The seals in the system may react differently to the types esters in the fluid and the different fluid viscosities. Most modern brake systems are not as sensitive, so as far as you're concerned, the most important characteristics are probably price and boiling point.

What the heck is all this DOT stuff?

Primarily, the DOT ratings refer to boiling point, but the chemical composition of each fluid also makes them all slightly different when it comes to water absorption.

DOT3, DOT4, and DOT 5.1 are glycol based fluids and are highly "hydroscopic." They readily absorb water; don't keep unsealed bottles around for longer than a few weeks! DOT5 is a silicone based fluid that is not hydroscopic, but cannot be mixed with non-silicone based fluids and is more compressible than non-silicone based fluids.

	DOT 3	DOT 4	DOT 5	DOT 5.1
Dry BP @ 0.0% H2O	401°F	446°F	509°F	509°F
Wet BP @ 3.7% H2O	284°F	311°F	356°F	356°F
Chemical Composition	Glycol Ether	Glycol Ether/Borate Ester	Silicone	Glycol Ether/Borate Ester

Brake Fluid	Spec	Dry Boiling Point	Wet Boiling Point	Suggested List Price
Castrol SRF	DOT5.1	590°F	518°F	$69.99/33.8oz.
Neo Super DOT610		610°F	421°F	$15.00/12oz.
Motul RBF600		593°F	420°F	$15.00/16.9oz.
AP Super 600*		590°F	410°F	$18.00/16.9oz.
ATE Super Blue		536°F	392°F	$11.99/33.8oz
Motul DOT5.1		509°F	365°F	$6.50/16.9oz.
Valvoline Synpower	DOT4	503°F	343°F	$4.97/16.9oz.
ATE Sl		500°F	329°F	$7.95/16.9oz.
Castrol LMA		450°F	311°F	$3.50/16.9oz.
AP 551	DOT3	527°F	302°F	$12.50/16.9oz.

• Even though AP600 is technically a DOT5.1 fluid, it should not be mixed with any other fluid.

You can find more information here and here.

Which one should I use in my S4?

Many S4 owners who track their cars opt for Motul RBF600. Otherwise, any DOT4/DOT5.1 fluid should be fine. Some people have reported problems with ATE Super Blue in the B5 S4, specifically squeaky clutches. Also, avoid DOT5 fluids, as they are compressible and do not mix with the others.

Where can I find quality DOT4/DOT5.1 fluid?

Most automobile parts retail shops (PepBoys, Autozone, etc.) do not carry "boutique" brake fluids like Motul. Your best bet is to find a local race bike shop that carries it. There are also several online stores that sell Motul via mail.

What do I need to know about stainless steel brake lines?

If you are running stock calipers, replacing the lines with stainless steel is unlikely to improve things noticably. The stock setup already uses quite a bit of hardline from the fender well to the brake, and there is only a very short length of soft line in the OEM setup. If you choose to go the aftermarket caliper route, however, the front hardlines are usually removed, so stainless steel lines are recommended, since you'll need replacement lines anyway. Stoptech has a good writeup here.

My trip computer is displaying "(0)". Besides making me think of a vagina, what does this mean?

It means that your brake pad sensor has been tripped.

Do I have brake pad sensors on the rear?

No, only on the front.

How do I cycle the ABS pump with a VAG when flushing/bleeding brake fluid?

[03 - ABS Brakes]
[Basic Settings - 04]
Group 002
[Go!]

How do I bleed my brakes?

The rule of thumb is "furthest from the master" to "closest to the master" - outside to inside (for calipers with two bleed valves), left to right, back to front.

Two good references are Stoptech's white paper and these instructions for a 1.8T, but the process is the same. FYI, the S4 uses an 11mm bleed fitting.

Stock

What are HP2s?

The stock front calipers

Are my stock calipers fixed or floating?

Floating.

How many pistons are my stock brakes front and rear?

Two pistons up front, one piston in the rear.

How do I change the pads in my stock brakes?

The fronts are extremely easy. Morgan's writeup. The rears are a bit more difficult, but both are DIY jobs. It's for an A8, and the only difference is the shape of the spring tensioners on the pads. On the S4 rear pads, the springs are shaped like a V and fit against the caliper (pushing the pad towards the hub) - look at the stock pads before you remove them, and it will make sense.

BBK

What's a BBK?

A "big brake kit."

Why do I need a BBK?

1. You are all show, no go, and you want to make your car look blingity bling
2. You drive aggressively and fade the stock brakes
3. You want increased pad selection

Is a BBK install a DIY job?

It can be. It helps to observe one first, but it's pretty straightforward. Just realize that if you screw up, you likely won't know it until you really need to stop, at which point you might wish that you paid a professional. Most BBKs come with detailed install instructions, but go here for a brief overview of what's involved.

Will my car stop shorter with a BBK?

If you're using comparable pads in both setups, probably not. BBKs are all about fade resistance and pad selection (and bling for some people). When compared to the stock brakes, stopping distances are usually longer by a foot or two. However, under repeated applications, the stock brakes will fade quickly, increasing stopping distance. Buy a BBK because you need repeated stopping consistency. A BBK will resist fading longer. However, a BBK with street pads will still fade, so the proper pads for the intended use are important. Don't worry if you fade your BBK street pads on a bedding run - that's an abnormal use for street pads, and they'll work fine on the street under street conditions.

What happens to the brake pad sensor when I install a BBK or use pads that don't have pad sensor wires?

Unless you short the wires, the vagina light will be on all the time.

How do I short the pad sensor wires?

1. Clip the connector off and solder the wires together
2. Clip the wire from an old pad, couple the connectors, and solder the wires
3. Shove a single u-shaped piece of wire in the terminals of the connector.

2) and 3) allow you to keep your stock wiring intact should you ever want to use the sensors again. Check this tech article for more information

I installed a BBK or I am running non-Audi pads. I no longer have pads that use the sensor, and I don't want to rig up any jumpers. How do I get rid of the vagina light using VAG?

Note - this may not work on some model years (2000 and 2001). In that case, you may have to cut & solder the wires or jump the terminals on the sensor harness.

[Select]
[17 - Instruments]
[Recode - 07]
Write down the existing coding for future reference. 
Enter 5-digit code from below
[Do It!]

Look at the first two digits in the coding. Add the values for the options together to get the correct coding.

 00 - No available equipment
+01 - Brakepad wear sensor warning active
+02 - Seatbelt warning active
+04 - Washer fluid level warning active (may only work with pre-2000 models) 
+16 - Navigation System (non-USA models)

What are some of the common BBKs that fit under stock wheels?

Depends on rotor size. Any kit that uses rotors larger than 332mm probably will NOT fit. The Stoptech 332mm kit, STaSIS/Alcon 13" kits, ECS stage 3 (Porsche Big Red) are all known to fit under the stock 17" AVUS wheels.

Do I need to upgrade my rear brakes?

That depends. If you just drive on the street, the OEM rears (and fronts, to be honest) are usually fine. If you upgrade only the rears, you risk moving the brake bias rearward, which is not good if you are starting with a balanced system. Most people consider upgrading the rears only after upgrading the fronts. Some people still just go for some slotted rotors in the rear and call it a day. There are many options to choose from, including Stoptech, ECS, and STaSIS for size upgrades, and there are several vendors of slotted OEM style rear rotors, such as ECS and DBA. Note that most aftermarket rear calipers DO NOT come with integrated parking brake functionality, unlike the stock S4 rear calipers. However, Stoptech offers a separate E-brake caliper, and there are kits to allow S8 rotors and/or calipers to be used with the S4.

References

O.W.Kenobi's Audiworld post