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Brake fluid and clutch bleeding and flush - mk3 and mk4 VW and Audi
How to bleed/flush the brake and clutch fluid on your mk3 or mk4 Volkswagen
related links: 1000q: mk4 Passat brake fluid change, 1000q: mk5/6 VW Jetta/Golf, Audi A3 brake fluid change
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 Any and all information presented on this website is superseded by the official service manual and is not a substitute for the services or advice of a certified professional mechanic.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 or loss of control so have your local garage do it if you're not qualified to work on the brakes.
This article shows a few different ways to bleed the front/rear brakes and clutch fluid. The pictures are from a mk4 VW TDI, mk3 VW are similar. For mk4 Passat or mk5/mk6 cars, please see the related links above. The procedure can be also be used on non VWs except many cars have separate clutch and brake fluid reservoirs. Your TDI uses the same reservoir for both the clutch and brake. If you have an automatic transmission, you don't have a clutch or clutch fluid. For general tips on braking and why you have to flush the brake system, see 1000q: general brake FAQ. To do a brake job on your a4 body TDI, see 1000q: a4 brake job. For a brake job on your mk3 body TDI, see 1000q: front brake.
The recommended method in the service manual is to bleed under pressure. Pressure bleeding is the easiest so if you've never bled brakes before, just buy a pressure bleeder. Motive sells a pressure bleeder with the correct adapter to match the VW 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 pressure brake bleeders use a diaphragm to separate the pressure and the brake fluid but they also need to hold gallons of fluid for many jobs.
The DOT 4 brake fluid used on your TDI absorbs moisture so that water will not concentrate in the corners and form rust. Although most VW fluid reservoirs don't have a weep hole, many types of reservoirs do have a weep hole. If you don't change the brake fluid then corrosion may occur in the brake calipers, clutch slave cylinder, or master cylinder, causing a leak or poor action. Under repeated heavy braking, the brake fluid could boil, causing loss of braking authority.
Brake/clutch fluid is poisonous and highly corrosive to paint! If a drop falls onto your paint, stop and dab the drop off, then wipe it clean with a damp towel. Follow up with soapy water. If you don't wipe it clean now, it will eat a hole in the paint down to the metal. Always wear gloves and comply with all safety precautions as specified in your factory service manual when handling the fluid. 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.
If you have any questions about bleeding the clutch or brakes on your VW, don't hesitate to ask in the Volkswagen forums here: myturbodiesel.com forums
Some common issues that can be solved by bleeding the brakes are soft or spongy brake pedal or poor braking action. If you need two pumps to firmly actuate the calipers, then you probably have an air bubble in the brake lines. The air bubble prevents all of the force of the pedal from going to the slave cylinder and fully releasing the clutch. Since air bubbles can be compressed whereas hydraulic brake fluid cannot, even small air bubbles will degrade pedal feel and prevent smooth brake or clutch action. 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 brakes because it may have sucked in air.
If air got into the lines, also bleed the ABS pump, if equipped. Plug in your VCDS diagnostic cable 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 until there's no air in the brake lines and 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.
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.
Caution: DO NOT use DOT 5 fluid (silicone based) in a VW system - it's not compatible with the seals or DOT 3/4 fluid. DOT 5 (silicone based) is not the same as DOT 5.1 (yes 5.1 was poorly named)! Do not use old brake fluid. Brake fluid absorbs moisture from the air and should be kept in an airtight, unopened container.
DOT 3, 4, super DOT 4, and DOT 5.1 brake 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 than 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: VW used to recommend FMVSS 116 DOT 4 brake fluid. Your service manual and the fluid cap probably says super DOT 4. For cars model year 2006 and newer they recommend VW specification 501 14 brake fluid. VW spec 501 14 fluid is supposed to have lower cold viscosity compared to 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 anyone who sells this new spec fluid and if you go to the dealer they will hand you a bottle of DOT 4 fluid for twice the price. ATE SL.6 and Pentosin DOT4 LV (low viscosity) are probably the closest to the VW spec fluid because they are advertised to be thinner specifically for ABS/ESP systems. If you have an earlier car without ESP stability control I don't think it will make any difference and VW 501 14 fluid is fully compatible with DOT 3/4.
Brake fluid that is probably closest to VW specification 501 14 (doesn't say it on the bottle though)ATE SL.6
Pentosin super DOT 4 LV
Other fluids that will work if you can't find the above fluids or if you don't have ESP
OEM DOT 4 brake fluid VW# b000750m3 (1 liter size) from ecstuning
Any DOT 4 fluid from your local auto parts store
Brake bleeding procedure
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. See 1000q: jack points to see how I raised my mk4 Jetta TDI. If you have ramps or a lift, it's easier to get to the brake bleeder nipple without removing the wheel. Here are pictures of the 11mm bleeder nipples. Each is covered by a rubber cap. All calipers have the bleeder nipple on the top of the caliper. This is because it helps let out air bubbles and helps prevent air from getting in. I still try to avoid opening the bleeder unless fluid is moving out, either through vacuum or pressure.
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 brakes.
Don't dispose of the used brake fluid onto the ground! Earth911.com has a search function to find your local waste disposal. Remember, brake fluid also eats up car paint so wipe up any spills immediately!
First method to change fluid (manually)
If you do not 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 cylinder (pictured below) gets pushed forward and 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 again because air is probably 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 further.
With non ABS cars, I recommend front brakes, then rear brakes, then clutch.
With ABS cars, the factory service manual recommends bleeding calipers in the following order (for mk4 VW Jetta, New beetle, or Golf).
Right Rear, Left Rear, Right Front, Left Front
Left Front, Right Front, Left Rear, Right Rear
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 won't "slide" back. Pictured below is an example of a hose loop.
Bleeding the clutch fluid
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 doesn't build pressure like pumping a 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.
This is why I prefer to use the other methods of changing the fluid - they are be faster and have less chance for air to get in.
Pictured below is the slave cylinder in green and the bleeder in red. This is on top of the transmission. The nipple should be a 11mm hex.
Second method of changing fluid (vacuum)
Bleeding with a vacuum pump is easier than bleeding manually. 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 bubbles came from inside the system or are being drawn outside because of the vacuum. Therefore, I feel that using a mity-vac type device to bleed the brakes is not great. A hand vacuum pump is a great shop tool but not for bleeding brakes. 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 use an electric vacuum pump with enough force to quickly suck out the fluid. It is very similar to the manual method, only you don't need a helper to pump the pedals.
First, apply suction to the bleeder nipple. This is pictured below. Make sure you have suction before you open the bleeder! Loosen the nipple until fluid comes out.
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. The only problem with this is that if the hose isnt' tight against the nipple, bubbles will enter the hose so you can't tell if it's air from the brakes or air from a leak around the hose.
If you didn't see it above, the factory service manual recommends bleeding calipers in the following order (mk4 Jetta, Golf, New Beetle).
Right Rear, Left Rear, Right Front, Left Front
Left Front, Right Front, Left Rear, Right Rear
Third method of changing fluid (pressure)
The last method involves using a power bleeder that applies fluid at the reservoir under pressure. This is pretty much the same idea as the last two methods, but the instructions for your specific model of power bleeder supersede any tips here. The factory service manual states that you should not exceed 14.5 psi of pressure due to the proportioning valve inside the ABS system which prevents a good flushing. I would limit the pressure to about 10-12 psi.
This is the easiest and fastest method since the bleeder supplies fresh fluid and you don't have to worry about running 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. The biggest advantage of this method is that unlike a vacuum pump, you won't see any air bubbles in the line unless they came out of the lines. This is also the recommended method by the factory service manual since it can help get air out of the ABS pump.
You can use a milk jug to catch the fluid - the hollow handle holds the tubing end well.
Purging air out of the lines
If you did get an air bubble in the lines while bleeding, you must get it out. If your car is equipped with ABS 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 will cycle the ABS pump and it's 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 a re-circulating purge on the brakes is not a good idea because the brake lines/nipple are much 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 all 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 the brake fluid is so important to brake safety, please ask in the TDI forum before starting if you have any questions.