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 Any and all information presented on this website is superseded by the official service manual and is not a substitute for the services or advice of a certified professional mechanic.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.
Since all Passat TDI in North America are automatic tiptronic transmission, refer to your service manual if you have a manual transmission car. The difference is that you have to bleed the clutch first. Auto transmission cars do not have a clutch cylinder to bleed. Have more tips? Are there broken links or pictures? If you have any questions, please ask it in the mk4 VW Passat TDI forums.
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 Passat see 1000q: brake job Passat.
The recommended method in the service manual is to bleed under pressure of at least 2 bar. The suggested pressure for most other TDI is 1 bar. The difference is probably due to the different ABS pump. 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 over time. You'll only be using the fluid for an afternoon.
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. When the system heats up and cools down, some moisture or air can enter the system. If you don't change the brake fluid when it's dirty or contaminated then corrosion may occur in the clutch slave cylinder, master cylinder, or brake caliper, causing a leak or poor braking. Under repeated heavy braking which generates heat, the brake fluid could boil, causing loss of braking authority. Water lowers the boiling point of brake fluid.
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. Use a funnel - it will make this job easier.
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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. If you step on the brake pedal and it sinks, you have air in the lines, a fluid leak, or faulty master cylinder or brakes. 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, you must also bleed the ABS pump. Plug in your VCDS diagnostic cable and select module 3 - ABS brakes. Go to Basic settings and select group 2. Hit "Go!" This triggers the ABS pump. While it's circulating fluid you should bleed the system at each corner. 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. 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. Ideally, you should also briefly run the pump while bleeding the brakes to flush it out too.
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.
Related links: 1000q: how to change the rear brakes on your VW Passat TDI
VW brake and clutch fluid: DOT 4 fluid only - you'll need 3 quarts to
jack and jack stands
brake bleeder tool and hose (optional but highly suggested)
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. 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. It's covered by a rubber cap. All calipers have the bleeder nipple on the top of the caliper because it help prevent air from getting in and lets bubbles at the top out. I still try to avoid opening the bleeder unless fluid is moving out, either through vacuum or pressure.
Here is the other side with the rubber cap to the bleeder nipple still on.
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 basic ways to bleed the brakes.
Do not dispose of used brake fluid on the ground or sewer! Earth911.com can find your local brake fluid waste drop off.
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 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.
All Passat have ABS. Some have ASR (traction control) and some have ESP (stability control).
The factory service manual recommends bleeding the brake calipers in the following order for the 2004-2005 Passat TDI:
1. Right rear
2. Left rear
3. Right front
4. Left front
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 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 for the 2004-2005 Passat TDI:
1. Right rear
2. Left rear
3. Right front
4. Left front
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 supercede any tips here. The factory service manual states that you should use at least 2 bar of pressure. Due to the amount of pressure, make sure the seal on the reservoir cap (the one on the car) is seated and tight or else you'll have a major fluid leak.
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.
There are commercially available brake pressure bleeders but if you want to make your own, see 1000q: DIY brake pressure bleeder.
Pictured below is a power bleeder on use on a Jetta mk4 and
Audi A4 (same as Passat but your reservoir may look different).
You can use a milk jug to catch the fluid. The hollow handle of the jug
holds the end of the tube in place.
If you got an air bubble in the lines while bleeding or replaced a brake part which opened the lines, you must get all the air 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 prompt to activate the pump. This is the only way to get air out of the ABS pump other than taking it to the dealer and having them bleed the whole system. Below are some tips.
Start the VCDS software and plug the cable into the OBD2 port. Look for
the green LED on the cable. Go to Select to get to the control modules.
Click on ABS Brakes. Passat tend to have abs module problems. If
you can't connect, keep trying. If you have an abs module problem you can
have them rebuilt or buy a used one. Audi A4 had similar parts but check
that the Bosch part number is the same.
Select output tests and it will give you prompts. You'll hear the ABS
pump buzzing. That means that the pump is running. 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 this technique for the brakes is not a good idea because the brake lines/nipple are more likely to be dirty and the hose needed would have to be long. The likelihood of contaminates entering the master cylinder is greater with the brakes but low with the clutch. Even still, this method works as long as the fluid is totally clean.
Caution: again this method may only be used 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.
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