Disclaimer: Before you attempt any brake work on your car, refer to the factory service manual and follow all precautions. Any and all information presented on this website is superseded by the official service manual and is not a substitute for the services or advice of a certified professional mechanic. See the TOS Agreement for the full legal disclaimer. If the brakes are faulty or not working correctly, tow it to a mechanic and do not attempt to drive the car. Faulty brakes can result in an accident and/or loss of control so have your local garage do repair work if you're not qualified to work on the brakes.
The pictures are from a mk5 Volkswagen Jetta TDI. The Audi A3 TDI and other mk5-mk6 VW should be similar but refer to the official factory service manual before working on the car. Your VW/Audi uses the same fluid reservoir for both the clutch and brake. If you have a DSG transmission you don't have a clutch fluid bleed point. For general tips on braking and why you have to flush the brake system, see 1000q: general brake FAQ.
Related links: To do a brake job on your mk4 a4 body (Jetta, Golf, New Beetle) VW, see 1000q: a4 brake job. For a brake job on your mk3 TDI, see 1000q: front brake. To bleed the clutch on a mk4 a4 VW, see 1000q: mk4 brake and clutch fluid bleed. There are a few small differences.
The service manual says to use a pressure bleeder. I also suggest using this since it'll make it much easier and faster. It also makes bleeding brakes a 1 man job. Motive sells a pressure bleeder with the correct adapter to match the VW/Audi fluid reservoir cap. If you would like to make your own pressure bleeder, see 1000q: DIY brake bleeder. The disadvantage of a home pressure bleeder is that air pressure and moisture are exposed to the clean fluid. Professional level pressure brake bleeders use a diaphragm to separate the air from the brake fluid but they also need to hold gallons of fluid for many jobs and the fluid sits there for a while before being used so they can't expose it to air.
Air bubbles in the brake fluid can also cause a soft or spongy brake pedal. If the brakes have to be pumped to actuate the calipers, you probably have an air bubble in the lines. Hydraulic brake fluid isn't compressed whereas the air bubble is. This prevents the caliper from actuating. If you just replaced the brake lines or let the fluid level on the fluid reservoir go below "min" you will also need to thoroughly bleed the ABS system with a VCDS diagnostic cable.
To bleed the ABS system, plug in your VCDS and select module 3 - ABS brakes. Go to Basic settings and select group 1. Hit "Go!" This triggers the ABS pump, during which time you should bleed the system. To build higher pressure than what is possible with a brake bleeder, do the manual "helper pumps the brakes while you bleed method" method. Do this a few times after there's no air in the lines. Do this a few times after there's no air in the lines. Repeat until there's no more air in the brake fluid system. This shouldn't take more than 1 minute of running the pump per corner but your situation may vary so consult a professional if you're not sure.
The factory recommendation for changing the fluid is every 2 years regardless of mileage. If it's not changed, corrosion may occur in the brake calipers, clutch slave cylinder, or master cylinder, causing a brake fluid leak or poor braking authority. As the fluid ages its boiling point lowers. If brake fluid boils than you will lose braking authority.
Brake/clutch fluid is poisonous and highly corrosive to paint! If there's a spill on the ground, wipe it up and wash clean - if you accidentally pollute, at least dilute! If a drop falls onto your paint, stop and dab the drop off, then wipe the paint clean with a damp towel. Follow up with soapy water. If you let it sit on the paint it'll eat a hole down to the metal. Always wear gloves, wear eye protection, and comply with all safety precautions listed in your factory service manual when handling the fluid or working on the car. I suggest putting some paper towels around the master cylinder reservoir and using a funnel to add fluid. Don't be lazy and not use a funnel.
You should also always use the parking brake when parking. This is good practice in any car, but in your VW, it resets the rear caliper self adjusting mechanism. Not applying the parking brake can result in poor braking.
Earth911.com can search for a local waste disposal for brake fluid and other car fluids.
Caution: DO NOT use DOT 5 fluid (silicone based) in your brake fluid system - it's not compatible with the seals or DOT 3/4 fluid. DOT 5 (silicone based) is not the poorly named DOT 5.1! Do not reuse old brake fluid. Brake fluid absorbs moisture from the air and should be kept in an airtight, unopened container.
DOT 3, 4, and super DOT 4 fluids are fully compatible. DOT 3 has a
lower boiling point, DOT 4 has a higher boiling point, and super DOT 4 is
supposed to be even higher. Again, DOT 5.1 is totally different from DOT 5
silicone based fluid!
-DOT 3 minimum dry boiling point 205°C (401°F), minimum wet boiling point 140°C (284°F)
-DOT 4 minimum dry boiling point 230°C (446°F), minimum wet boiling point 155°C (311°F)
-DOT 5.1 minimum dry boiling point 270°C (518°F), minimum wet boiling point 191°C ( 376°F)
Caution: Your service manual and the fluid cap probably says super DOT 4 but VW and Audi recommend VW specification 501 14 brake fluid. VW spec 501 14 fluid is supposed to have lower cold viscosity compared to FMVSS 116 DOT 4 fluid which results in faster response of the fluid through the tiny holes of the ESP/ABS (anti slip regulation/antilock brake) system. The problem is that I don't know where you can find this new fluid spec. If you go to the dealer they'll sell you a bottle of DOT 4 fluid for twice the price. Pentosin DOT4 LV (low viscosity) and ATE SL.6 are designed to be thinner than the average DOT 4 fluid for ABS/ESP systems and are probably the closest to the VW spec fluid.
Brake fluid that is probably closest to VW specification 501 14
(doesn't say it on the bottle though)
Pentosin super DOT 4 LV
Other fluids that will work if you can't find the above fluids
OEM DOT 4 brake fluid VW# b000750m3 (1 liter size)
Any DOT 4 fluid from your local auto parts store
If you have a manual transmission, first remove the air intake box to get access to the bleeder nipple. See 1000q: air box removal for details. The bleeder is on the top of the slave cylinder which is on top of the transmission.
You may have to jack up the car and remove the wheels to get to the bleeder nipple on the brakes. Securely rest the car on jack stands before getting under the car - never get under a car if it's being supported by only a hydraulic floor jack. If you have ramps or a lift, it's easier to get to the brake bleeder nipple. Here are pictures of the 11mm bleeder nipples (front brake picture below is from an older car)
The nipple should be covered
covered by a rubber cap. The bleeder is always on the top of the caliper because it helps
any air escape and discourages air from getting in. Even still, try to avoid opening the bleeder unless
you're bleeding the brakes and getting fluid out.
Air box and battery box removed for illustration (view is looking down at the
transmission). The angle is awkward so make sure you're not stripping the
Remove the rubber cap and check the size of the wrench around the bleeder. It should be 11mm but aftermarket calipers or replacement bleeders sometimes have differently sized nipples. If the bleeder nut gets damaged, a new one can be purchased at autozone, napa, or any other auto parts store.
Below are the 3 ways to bleed the fluid. Bleed it in the following
Clutch (if equipped)
Note - during bleeding, remove at least .15 liters from the bleeder valve/clutch slave cylinder (if equipped) and at least .25 liters from each brake caliper bleeder.
The suggested method of bleeding the brake fluid (pressure)
Any instructions for your specific model of power bleeder supercede any tips here. The factory service manual states that you should have at least 30 psi (2 bar) of pressure to get the old fluid out of the hydraulic unit. I assume they mean the ABS pump. This is the opposite of earlier models where you couldn't exceed 1 bar for proper bleeding.
The biggest advantage of pressure bleeding is that unlike a vacuum pump, you won't see any air bubbles in the line unless they came out of the lines. It's also a 1 person job. If you bleed manually you need 2 people. You're also less likely to run the the reservoir low (as long as the bleeder is full). All you do is open the bleeder nipple and lead the nipple hose to a waste container.
There are commercially available brake pressure bleeders but
if you want to make your own, see 1000q: DIY
brake pressure bleeder. Attach the adapter cap to the brake fluid
reservoir and fill the pressure bleeder. Note the position of the feed
line inside the pressure bleeder - in case you start to run low you can tilt the
unit to that side. Pump it to at least 2 bar (30 psi).
You can use a milk jug to catch the fluid. If you snake the tubing end
into the hollow handle it'll hold the tube and let you see fluid movement. Open the bleeder and the fluid will come out by
itself. You can also slowly pump the brake pedal to raise the bleeding
pressure and help clear out the ABS pump. Close the nipple before
When you're done, remove the adapter cap and suck any excess fluid out of the reservoir.
Manual method to change the brake fluid on your VW or Audi A3
If you don't have a vacuum or pressure bleeder, have another person pump the brake pedal a few times then press and hold the brake pedal down. This pressurizes the system. Then open the bleeder screw to let the fluid out. This will relieve the pedal pressure. Have them keep the pedal down until you close the bleeder. Pumping the brakes when bleeding is okay, pumping the clutch is not recommended, more in the next section. Once fluid almost stops flowing out, close the bleeder screw so that they can raise the brake pedal. Repeat. See how using a vacuum or pressure bleeder is better? The other problem is that the master cylinder seals never go all the way to the bottom of the cylinder - pushing the pedal all the way down (beyond the normal range of travel) wears them out a little bit.
The advantage of manual pedal bleeding is that it builds much higher pressure in the brake system to push out any old fluid. If you are bleeding the ABS pump I suggest using the manual pedal method with a pressure bleeder to keep the fluid topped off and moving out.
When you press the brake pedal down, a piston inside the metal master cylinder cylinder is pushed forward which pressurizes the fluid in the brake lines. If air gets down to the level of the cylinder opening, you will hear a sucking sound from air entering the cylinder. If it gets so low that you hear sucking, bleed the entire system and the ABS pump again because you got air in the brake lines!
To prevent this while bleeding, keep the fluid level in the brake fluid reservoir above the
"min" line. About every 2-3 full pedal bleeds is a conservative
estimate for the fluid level to go from max to min. If the fluid does not go down
easily then the filter on the
reservoir is clogged - STOP, remove the filter and clean it before going any
Another manual method is to use speedbleeders (I don't
like them due to possible failure of the springs or getting jammed/clogged), or with a hose
loop. A hose loop is when you tie a clear hose in a vertical loop of
sufficient height and SLOWLY pump the
pedal. If you pump the pedal quickly, any air bubbles present won't "slide"
back. Pictured below is an example. If using this, have a helper
watch it to make sure the air bubbles aren't sliding back into the caliper.
Bleeding the clutch fluid manually
Since the brakes and clutch share the same fluid reservoir, you should bleed the clutch at the same time (manual transmission only). However, it should be bled differently if you are bleeding it manually, and this is why. When you pump the brake pedal, the brake calipers press against a rotor and don't go any further. The fluid in the lines is building pressure but not moving too much. When you press the clutch pedal, the clutch piston goes out and comes back in when you release the pedal. Pumping the clutch pedal does not build pressure like pumping the brake pedal and will cause large air bubbles to become small air bubbles that are harder to get out and notice.
So don't pump the clutch pedal when bleeding, have a helper push and HOLD down the clutch pedal, then you can open the bleeder (circled below in red) to draw out the fluid. This will relieve the pedal pressure, close the bleeder nipple and then the helper can raise the clutch pedal. Otherwise, it can suck in the old fluid or any air bubbles. If the pedal drops to the floor, just pull it up. Again, have your helper press and hold the clutch pedal, open the bleeder, let drain, close the bleeder, and then they can raise the clutch pedal. On your VW, the bleeder nipple is near the top of the clutch slave cylinder but on many cars it's on the bottom of the transmission.
Using vacuum to bleed the clutch and brakes
I've tried using hand vacuum pumps to bleed the brakes and it's definitely slower, more tiring, and more problem prone than with a pressure bleeder. A hand vacuum pump is an essential garage tool but if you're buying it just for the brakes, spend a little more and get a pressure bleeder. The main drawback of using a hand vacuum pump is that it may not be forceful enough to scrape every last bit of old fluid out of the lines. It's also harder to see if air bubbles in the line are coming from inside the brake system or are because of a poor vacuum seal at the bleeder. If the nipple is clogged, it can also cause a blockage for the vacuum pump. You can have someone pump the brake and bleed manually to get any possible blockage out first. The factory service manual recommends pressure bleeding because it can help get air out of the ABS pump. I used to use an electric vacuum pump with enough force to quickly suck out the fluid but after using a pressure bleeder I think the pressure bleeder is better.
Keep suction applied whenever the bleeder nipple is opened so there is no backflow. Check the fluid level in the master cylinder reservoir to make sure no air gets into the lines. If you have a helper, have them top off the fluid reservoir. When the fluid is fresh and clean, close the nipple.
Purging air out of the lines
If you did get an air bubble in the lines while bleeding, you must get it out. You must use a VCDS diagnostic cable or equivalent to cycle the ABS pump. After you plug in the cable and start the software, click on ABS pump. Then output tests. Cycle through them and follow the software prompts. This is the only way to get air out of the ABS pump. The service manual doesn't say how long to run the pump so as long as there's no air in the lines, 30 seconds per corner should be sufficient. I don't know the internals of the pump routing so if you bleed the brakes in sequence as before it should completely empty the pump. If air got into the lines, run the pump while bleeding until no more air is in the lines + about another 30 seconds. Your situation may vary so consult a professional if you're not sure if you got all the air out or bled the brakes correctly.
If you have fresh fluid and want to purge air out, try a re-circulating purge. This is best for the clutch since the hose is short and the fluid is more likely to be clean after you have fresh fluid. Using it on the brakes is not a good idea because the brake lines/nipple are more likely to be dirty and the hose needed would be long. The likelihood of contaminates entering the master cylinder is greater with the brakes but low with the clutch.
Caution: this method is ONLY if your fluid is clean and totally new! If you just flushed the entire system but got an air bubble in the lines during the last pump, you can use this method. If your fluid is dirty or old and not new, do not use this method since it will put dirt, rust, and contaminants into the brake reservoir, damage the master cylinder seals, etc. You MUST have ALL clean fluid in your system before you try a re-circulate purge.
Some cars have the clutch slave cylinder on the bottom of the transmission, making it easy to get air into the system. In these cases, getting tiny air bubbles out is very important or else you will lose clutch pedal feel and authority. Most bleeders are on the top of the cylinder to avoid letting air in.
Always use a clean tube used only for brake fluid! If the tube is not clean, the brake fluid must be discarded! Also make sure that the bleeder is clean and no dirt is in the fluid that comes out of the hose. The first few pumps should always be discarded.
First drain all of the old fluid using one of the methods above. Then connect soft silicone tubing from the bleeder and route the other end back to the brake fluid reservoir. Again, the first pumps should be discarded into a waste container. With the bleeder loosened, slowly pump. This recirculates the fresh fluid back to the reservoir and any bubbles will get worked out. As always, you must keep the fluid level above "min". You could also put a small filter at the reservoir if you feel there may be any contaminants in the line.
I also suggest taping a paper towel near the tubing ends to catch any drips. Brake fluid will strip the paint if it's not quickly cleaned off. If your hands or tubing have any fluid on them, wrap the tubing in paper towels as well.
Since bleeding the brakes are so important, don't hesitate to ask any questions in the myturbodiesel.com VW and Audi TDI forums