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Replacing Audi Brake Lines
 
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Pelican Technical Article:

Replacing Audi Brake Lines

Peter Bodensteiner

Time:

2 hours2 hrs

Tab:

$60

Talent:

***

Tools:

11mm flare nut wrench, power bleeder

Applicable Models:

 
Audi A4 (1997-01)
Audi A4 Quattro (1997-01)
Audi TT (2000-04)
Audi TT Quattro (2000-04)
VW Beetle (1999-02)
VW Golf (2000-02)
VW Jetta (2000-02)
VW Passat (1996-00)

Parts Required:

New brake lines

Hot Tip:

take your time threading the brake lines.

Performance Gain:

better braking

Complementary Modification:

Replace brake fluid

Stainless brake lines are a common upgrade for performance cars, but what are they, exactly, and why are they popular?

The brake lines in a typical car consist of hard metal lines, which run alongside or within the chassis, and flexible rubber lines, which are usually found between the chassis and the brake calipers. The flexible lines are used to accommodate the movement of the suspension of the car up and down and in the front, as the wheels steer left and right.

These rubber hoses work fine in most applications, and they're inexpensive, so pretty much every car manufacturer uses them. The beef with rubber lines is that, being rubber, they expand slightly when subjected to the hydraulic pressure that is created when the driver steps on the brake pedal. This causes the brake pedal to feel less than firm--in other words, the braking action of the car responds less directly, and with less direct feedback, to the actions of the driver than would be optimal.

This is where aftermarket stainless steel brake lines come in. In reality, only the braided exterior is metal; the interior is still rubber or another flexible material, but the braided exterior keeps any expansion by the flexible line in check. They also look really cool once installed.

Some drawbacks exist, though. First, the braided stainless line will rub its way through almost anything it comes into regular contact with. Second, the braided metal can collect debris over time, which can abrade the line itself and potentially cause fraying or even failure. In the end, this kind of line is most appropriately used on a race car, where brake lines need to be heavily protected from debris and on-track incidents, and where having a firm brake pedal is paramount. Race cars are frequently inspected and parts such as brake lines are replaced as a matter of course. Street-going cars typically don't undergo such a rigorous maintenance regimen.

Keep this in mind should you be thinking about switching over to these stainless steel brake lines. I'm not saying you shouldn't install them--after all, they do look cool--but keep an eye on them, and if you have any doubts about their safety, be sure to replace them.

As you're about to see, it's not all that difficult to make the swap on the A4. You'll need some brake line wrenches, which look similar to a regular combination wrench but with more contact surfaces to the fastener to prevent slipping. You can use the instructions in this project to replace the standard rubber hoses as well.

Once the lines are fitted, you'll need to bleed the braking system to remove the air introduced into the system. Please see our article on bleeding brake for more info.

Before you start, place a piece of plastic wrap underneath the brake fluid reservoir cap and replace the cap.
Figure 1

Before you start, place a piece of plastic wrap underneath the brake fluid reservoir cap and replace the cap. This will help prevent air pressure from pushing fluid out as you open up the braking system. You'll still leak out some fluid (to that end, make sure to have some rags and/or a drain pan at the ready), but this will help minimize the fluid loss.

There are six flexible brake lines on the Quattro A4: one to each of the front brake calipers and two at each rear corner.
Figure 2

There are six flexible brake lines on the Quattro A4: one to each of the front brake calipers and two at each rear corner. With the exception of the direct connection between the outboard rear hoses and the rear brake calipers, all of these lines connect the same way. Starting from the top in this photo, the hard line has an 11mm hex nut at its end. The nut is actually just the top part of a

Use an 11mm flare nut wrench to loosen the nut on the hard line.
Figure 3

Use an 11mm flare nut wrench to loosen the nut on the hard line. Once you have the connection loose, you can use an open-ended wrench to loosen the nut the rest of the way.

When the nut is all of the way out of the hose, the hose can be separated.
Figure 4

When the nut is all of the way out of the hose, the hose can be separated. It's easier to see the components of the brake line connection when it is apart. The threaded portion below the 11mm nut is visible, but the spring clip that surrounds the fitting is not pictured here.

Insert the new braided hose through the hole in the bracket, add the spring clip, and thread the fitting on the hard line into the new hose.
Figure 5

Insert the new braided hose through the hole in the bracket, add the spring clip, and thread the fitting on the hard line into the new hose.

As the nut is tightened (11 ft/lbs is the spec), the threads move further into the hose and the spring clip compresses.
Figure 6

As the nut is tightened (11 ft/lbs is the spec), the threads move further into the hose and the spring clip compresses. The hex on the end of the braided hose is a standard size--not metric--of 9/16" (however, you can use a 14mm wrench). This is often the case with aftermarket components, whereas factory parts will almost always have metric fasteners.

Here's the other end of the front brake hose.
Figure 7

Here's the other end of the front brake hose. In this case the hard line comes out of the caliper and runs back to the flexible hose. The connection is the same as at the other end, so you use an 11mm brake line wrench again to loosen it.

Loosen the nut until the hose is loose.
Figure 8

Loosen the nut until the hose is loose.

Insert the end of the braided hose through the mounting bracket and thread the coupling into it.
Figure 9

Insert the end of the braided hose through the mounting bracket and thread the coupling into it.

Again, the braided hose has a 9/16 fitting at the end, so you'll need a wrench of that size to hold it in place as you apply the final tightening to the 11mm nut on the end of the threaded coupling.
Figure 10

Again, the braided hose has a 9/16" fitting at the end, so you'll need a wrench of that size to hold it in place as you apply the final tightening to the 11mm nut on the end of the threaded coupling.

Here's a look at the whole new line as installed.
Figure 11

Here's a look at the whole new line as installed. Be sure there are no kinks, extreme bends, or twists in the line. Repeat the procedure on the other front brake.

At the rear of a Quattro-equipped A4, there are two segments of flexible brake hose.
Figure 12

At the rear of a Quattro-equipped A4, there are two segments of flexible brake hose. The inboard portion is equipped with two fittings that are identical to the ones on the front brake hoses. This is the inboard segment on the driver's side.

This is the counterpart on the passenger side.
Figure 13

This is the counterpart on the passenger side. This sequence of photos shows the connection together...

.
Figure 14

...with the threaded portion loosened and removed from the end of the hose...

.
Figure 15

...with the rubber hose removed...

.
Figure 16

...and with the end of the new hose in place and the threaded portion of the hard line inserted and partially threaded.

The outboard hose at each rear corner is a bit different than the others.
Figure 17

The outboard hose at each rear corner is a bit different than the others. The hose side of the connection has a 14mm hex that you must hold steady while loosening the 11mm nut on the hard line.

The main difference with this hose is that the hose end threads directly into the underside of the caliper.
Figure 18

The main difference with this hose is that the hose end threads directly into the underside of the caliper. You can see this connection in the center of this photo; it's a bit crowded in this area (green arrow). This means that you must detach the hard line side of this hose first, as in the previous step, so that you can twist this end of the line out of the caliper. Use a 14mm brake line wrench to remove the caliper end of the hose.

Here is a close-up of the end of the hose that threads into the caliper.
Figure 19

Here is a close-up of the end of the hose that threads into the caliper. It's a male fitting with threads on the outside, unlike the others, which are female fittings with threads on the inside.

Thread this end of the hose into the caliper and use a 9/16 brake line wrench to tighten it down.
Figure 20

Thread this end of the hose into the caliper and use a 9/16" brake line wrench to tighten it down.

When you install the other end of the outboard braided hose, you must again counter-hold the hose while tightening the hard line nut, but remember that the new line has a 9/16 hex on the end.
Figure 21

When you install the other end of the outboard braided hose, you must again counter-hold the hose while tightening the hard line nut, but remember that the new line has a 9/16" hex on the end.

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Comments and Suggestions:
Bahamit Comments: I'd just add that should your flare end wrench start slipping, stop, add more penetrating oil and heat, lots and lots of heat. With the way the fittings are, the nuts have a tendency to become very soft especially in the rear and I destroyed one of the hard lines out of necessity to get the nuts off in the rear because I didn't pull out the torch soon enough.
Otherwise annother impeccable write up, very helpful.
July 5, 2015
  Followup from the Pelican Staff: Penetrating oil is fine, however heat could cause a brake line to explode. Never apply heat the a brake line or hose, explosion and burns could occur. - Nick at Pelican Parts  

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