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Bleeding Audi Brakes
 
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Pelican Technical Article:

Bleeding Audi Brakes

Peter Bodensteiner

Time:

1 hour1 hr

Tab:

$0

Talent:

***

Tools:

9mm , 11mm wrench

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:

Power bleeder,

Hot Tip:

Lay down drop cloths to catch any spilled fluid.

Performance Gain:

Better braking

Complementary Modification:

Change brake pads

Bleeding the braking system is a fundamental task that any DIY-er should be able to do. Not only is it relatively easy to do, but it is a necessary part of any regular maintenance regimen and also brake system upgrades or repairs.

The goal of bleeding the brakes is to either remove old brake fluid from the system, to remove air from the brake lines. A brake system works on the principle that the brake fluid is non-compressible. The same cannot be said for air, which will compress under pressure. Therefore, any air in the brake system will hinder hydraulic pressure from reaching the calipers, where it has work to do.

In addition, brake fluid absorbs water from exposure to air over time. This water can have a corrosive effect on brake system components, and under extreme conditions, such as during track driving, the water in the system lowers the boiling temperature of the brake fluid. If the heat of braking causes brake fluid to boil, this also introduces compressible gas to the system and decreases braking effectiveness.

Drivers who demand a lot from their brakes are wise to replace their brake fluid on a regular basis, but everyday cars should also replace the fluid every two years or so. If you replace brake lines or calipers, you should bleed your brake system to remove any air that might have entered the system. Bleeding brakes is a perfect complementary project for changing brake pads.

The difference between bleeding brakes and flushing brakes is merely a matter of degree--if you bleed enough fluid out of the system that you have replaced all of the original fluid, you've flushed them. Some people like to switch between fluid of different colors of compatible, same-spec fluid with each change. When the "new" color of fluid emerges from the bleeder screw, the fluid in the system is fully changed.

If you are flushing all of the fluid, you can open the brake fluid reservoir and remove some of the old fluid there first, adding new fluid to top off the reservoir. This will give you less fluid to push out to the calipers before you're seeing new fluid. However you do it, you need to make sure you always keep an adequate amount of fluid in the reservoir. If you empty out the reservoir while you're bleeding the brakes, you'll suddenly be admitting air into the top end of the system, and then you'll need to thoroughly bleed the whole system again.

Removing the wheel is the best way to get at the bleeder screw on each brake caliper. It may be possible with some cars to bleed the brakes without removing the wheels, but I'd advise trying that only after you really know what you're doing.

You can either lift the whole car up and remove all the wheels or do one corner at a time. Either way, you want to start with the wheel furthest away from the brake master cylinder and work your way to the wheel closest to the master cylinder. In the case of our A4, this means an order of rear passenger-->rear driver-->front passenger-->front driver. Bleed fluid from each corner until you're getting new fluid (if you're flushing all the old fluid) or until you're not seeing any air bubbles in the system. Then you can move on to the next corner.

This process works best with a helper who can push on the brake pedal when you open the bleeder screw. There are devices that enable a single person to bleed brakes on their own--I've had experience with Speed Bleeders, which are replacement bleed screws that include a small check valve. You can also use a pressurized brake bleeder device. Both of these solutions are designed to prevent air from being sucked into the lines (which would defeat the purpose of bleeding the brakes in the first place). However, the simplest solution is to grab a helper who is willing to push on the brake pedal for a while.

If you decide to use a pressure bleeder to bleed the system, it's important to remember not to exceed 10psi when pressurizing the system. Pressure bleeders can literally "pop" brake fluid cylinders if over pressurized.

Start by removing the cap from the brake fluid reservoir under the hood.
Figure 1

Start by removing the cap from the brake fluid reservoir under the hood. This will allow atmospheric air pressure to help push brake fluid through your lines and out to the calipers as you bleed them. As noted, make sure the fluid is topped off before you start, and keep it topped off during the bleeding process. If you prefer to remove some old brake fluid from the reservoir, now is the time to do it. Suction it out of the reservoir and replace it with fresh fluid straight from a previously unopened bottle. Because of the hydrophilic nature of brake fluid, you want to limit its exposure to the air. Thus, you should only use new, unopened bottles of brake fluid when you're adding fluid to the system.

Move to the right rear brake caliper.
Figure 2

Move to the right rear brake caliper. Find the rubber cover on the caliper bleeder screw and remove it. Place an 11mm closed-end wrench or brake line wrench on the faceted portion of the bleed screw (green arrow).

Place some clear tubing over the end of the bleeder screw and push it down snug.
Figure 3

Place some clear tubing over the end of the bleeder screw and push it down snug. The clear hose will allow you to easily see the condition of the fluid coming out of the caliper. A small kit that includes a length of tubing and a plastic container is a cheap investment and available at any auto parts store, but you can make do with properly sized tubing and an old jar or soda bottle. Just be careful to clean up any brake fluid spills, and avoid getting it on painted surfaces, as it will damage paint. If it happens anyway, use plenty of water to rinse off the surface.

Have your assistant sit in the driver's seat and give the brake pedal a couple of pumps to build pressure in the system.
Figure 4

Have your assistant sit in the driver's seat and give the brake pedal a couple of pumps to build pressure in the system. The assistant should then push the pedal down and as they do so, you loosen the bleeder screw. The pedal will sink to the floor as the fluid escapes, and the assistant should hold it there while you close the bleeder screw again. If the assistant allows the pedal to come up while you have the screw open, it will create a vacuum that will pull air and fluid back into the system. Therefore the assistant should only act according to your direction. Here's a good sequence to follow: 1) call out "down" to your assistant to have them push on the pedal 2) open the bleeder screw 3) when fluid stops coming out of the caliper, close the bleeder screw 4) call out "up" to signal your assistant to let the brake pedal come back up. Keep going until you see no more bubbles in the fluid coming out of the caliper, or until you have new fluid coming out. When you're done with each caliper, tighten the bleeder screw back down, remove the bleeder hose, and replace the rubber cap for the bleeder.

As mentioned, you should keep an eye on the level of fluid in the reservoir as you remove it at the calipers.
Figure 5

As mentioned, you should keep an eye on the level of fluid in the reservoir as you remove it at the calipers. It's a good idea to check the level and top it off each time you switch from one caliper to another, if not more often. Once you've completed bleeding all four calipers, top off the brake fluid reservoir one last time and replace the cap. You should now have a nice, firm brake pedal and new brake fluid to boot.

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Comments and Suggestions:
Akai Comments: My mechanic has bled the braking system of my Audi A4 1997 model several times, but the system is still not ok. The pedal travels almost 3/4 before the brakes are felt. Please advice appropriately. Thank you.
November 7, 2016
  Followup from the Pelican Staff: Sounds like the master cylinder is faulty. Does it hold pressure when the pedal is pumped with the engine down? - Nick at Pelican Parts  
solobee Comments: i have a problem of fixeing cluch master cylinder of audi a4 2005 what can i do thank you
September 28, 2016
  Followup from the Pelican Staff: Replace it and the slave cylinder.

Give The Pelican Parts parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need. - Nick at Pelican Parts
 
Audi5000 Comments: I have a 2002 A4 Quattro 1.8T. I bled all calipers in the order you mentioned but, the pedal is pressed three quarters of the way down before the brakes engage. I bled the brakes while the car was on. Should I bleed them with the car off? I read I should disable the ABS, disconnect the battery and then bleed. Not sure if I need to do that or just bleed with the car off.
May 31, 2016
  Followup from the Pelican Staff: Bleed when the vehicle is off. battery connected. - Nick at Pelican Parts  
APF1982 Comments: do you know of anywhere that you can take your wheels from your vehicle and have them REE dipped in aluminum or and chrome. if you have a name of a location that does this I would be grateful to know it or if you knew somewhere that is near New Albany Indiana that would be great. Thank you very much. Or if there is a different solution that you would recommend instead of doing that please let me know what you would suggest. Thank you very much.
April 2, 2015
  Followup from the Pelican Staff: Try google or your local yellow pages for chrome platers. - Nick at Pelican Parts  
APF1982 Comments: what is the easiest way to compress the rear calipers on an audi a 4 quattro 2003 model sedan with a 3. o liter. I know that daywhat is the easiest way to compress the rear calipers on an audi a 4 quattro 2003 model sedan with a 3. o liter. I know that they twist in but do you use the it with the ratchet on like you are tightening a bolt or do you put the ratchet on where you are loosening a bolt? if there are any other bezel tricks that you know love when it comes to replacing rear rotors or calipers and had on that type of vehicle I would appreciate any knowledge that you could give me. Thank you
April 2, 2015
  Followup from the Pelican Staff: There is a special tool to retract the calipers.
Give our parts specialists a call at 1-888-280-7799. They can help you find the right tool. - Nick at Pelican Parts
 
APF1982 Comments: what does it mean when after you have bled all of your break and the pedal is not getting any better? I have an Audi a4 Quattro and don't know if that makes a difference on how you should bleed the brakes or if there is a certain procedure you should do because of the esp. please let me know if I am doing something wrong andif I am starting with the wrong will, I start with the right rear and then go to the left rear and then to the right right then to the left from. I'm not sure this is the correct order please let me know if it's not?, I start with the right rear and then go to the left rear and then to the right right then to the left from. I'm not sure this is the correct order please let me know if it's not? On
April 2, 2015
  Followup from the Pelican Staff: That bleeding order is correct.

Are you getting fluid out of all of the bleeders\? - Nick at Pelican Parts
 
Nickname Comments: NICE. Thank you very much
March 26, 2015
  Followup from the Pelican Staff: No problem. - Nick at Pelican Parts  

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