2007, 4.8 N62 Brakes: master cylinder & booster

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This is a success story. All is fixed. Sharing experience.

My search keywords when I had a problem, may help someone to find this post:

- brake pedal goes to the floor
- replaced master cylinder brakes still spongy
- replace master cylinder brakes still go to the floor

Few weeks ago I was driving down the hill and was not able to stop at a stop sign. Luckily there were no cars around so I managed to stop about 2 meters (6 feet) behind the stop line.

In general the brakes were “operational” (slightly) but they were not able to stop the car with the old way of driving/stopping. I managed to get home keeping the interval and braking in advance.

The braking pedal was extremely soft and I was able to touch the floor while braking.

I’ve googled and youtubed a lot. Everybody was saying it’s either an air in the system or master cylinder issue.
1) Braking fluid was changed, system flushed. A circle around the house – no success.
2) Ordered a new master cylinder. Replaced, flushed the system. A circle around the house – no success.
3) … learned how the entire braking system works, found schematics, videos etc.:

- did all tests on booster – everything was ok.
- tried to get rid of bubbles in the ABS-DSC with the computer but did not succeed, was not able to get any data from the car.
- decided to unplug the vacuum line from the, the braking pedal became hard as hell, but OMG(!) when forcing it down, I was able to stop the car quite sharp. Plugged the vacuum line back and tried to force the pedal OVER the “floor” position. And it worked! So what I was thinking is a maximum/lowest position, was actually not.
New (used) booster was ordered, replaced. System was flushed again and… that was it!

Conclusion: bad brake booster can be not only too hard but it can also be too soft.

There are few good video on booster replacement, but this is what I did.
So... E70 2007 4.8 brake booster replacement steps:

1) Remove the plastic cover over the brake fluid tank
2) Remove the rubber seal (just pull it up) and unscrew/remove the plastic… not sure how to name it, but another long piece of plastic which was under the rubber seal. You need to access those hydraulic metal pipes and a vacuum line.
3) Remove a small plastic holder to free the hydraulic lines. Just pull up the closest end.
4) IMPORTANT(!!!!) cover all you can with cling wrap, cloth, paper towel and secure it with tape. You WILL have a braking fluid spill and it’s extremely corrosive. When I replaced my master cylinder a week ago, I spilled some on an old brake booster. After 3-4 days when I received a new one there was NO PAINT on the old one, where the braking fluid drops were left. That’s not a joke!
5) Open the tank cap and cover BOTH: the cap and the tank opening with a cling film (sandwich wrap), or extract the fluid if you like (you’ll have to tilt the tank together with master cylinder and fluid may spill).
6) Pull the vacuum line from the booster (just pull forward, no screws or threads)
7) Loosen 2x 13mm (not 100% sure) nuts that hold the master cylinder to a booster.
8) Loosen 2x hydraulic lines from the master cylinder (not sure, but I think it’s 11mm). You may want to use special line wrench (google it).
9) Undo those 2x 13mm nuts from the booster
10) Undo hydraulic lines and pull them out. They’re metal, but have some flexibility. Now you gonna have brake fluid leaking from the master cylinder. You’ll have to plug openings somehow. Rubber cups are preferable, but fingers, cling wrap will do the job as well (just make sure nothing will stay inside when you’re done.
11) Remove the master cylinder and place it somewhere far-far away. Cover the hydraulic lines with cling wrap (you don’t want any dirt or extra spill). Pull the lines out the way.
12) Get inside the car, remove the black panel that is blocking access to the pedal connections (3 philips screws I believe)
13) If you have the speaker there, pull the cable out
14) If you have light there, turn the bulb with the cable 45 or 90 degrees and pull it out.
15) Remove the vent duck (2 or 3 torx screws)
16) Remove a clip that is holding a brake pedal towards a brake booster with a flat screwdriver and pull the pin out.
17) Undo 2x nuts holding the brake booster. It’s the same 13 mm as outside nuts.
18) Now the most complicated part: go outside and pull the booster out. Just find the right way. I had to compress it a bit, same as the brake pedal would do while braking (hard, but managed with hands)
19) Install the new one same way. Here you may need a helper to guide the bolts from inside.
20) That’s it. Just follow all steps in reverse order. You’ll need to bench bleed the master cylinder (check youtube), and install it back.
21) It may be a good idea to replace a gasket in between the master cylinder and a brake booster. I had a new cylinder that came with a new gasket and rubber plugs.

When you’re done, make sure you wipe AND WASH all painted spots where you had your brake fluid spills.

Flush and bleed you brake system. To be honest with you I didn’t check E70 manual, but most sources are saying to start from the furtherst wheel caliper from the cylinder. In my car (most E70s?) 2 hydraulic lines are going from the master cylinder to the ASC/DSC/ABS (one of those), that is on the RIGHT side, next to the AC lines and right head beam. So I assume that we have to start from the RearLeft wheel (I MAY BE WRONG, check the manual, but that’s what I did).

As I said earlier I didn’t manage to get a computer connection to the car to have a proper computer bleed. But I’ve found a very good advice: when your brakes are good enough to activate the ABS – do it. Speed up and brake hard enough to activate the ABS. Do it couple of times and bleed the system again. This helped me to get rid of few tiny bubbles.

All together booster replacement took me about 1 hour + 20 minutes to flush the brakes. Comparing to my recent oil cooler gasket replacement it’s a VERY easy job.

Price: New master cylinder with gasket $98, used 2012 brake booster (new part number, but fit perfectly) from ebay $120. Labor – priceless as it was done by myself

Tools: you’ll need few wrench extenders, set of metric sockets (preferably deep/long) 13mm(?), spanner 11mm(?) (preferably line wrench) /check the sizes somewhere or have spare sizes as I’m not 100% sure now/, philips + flat screwdrivers, torx male bit for vent duck. Lots of cloth/towels and cling wrap.

If something is unclear, please feel free to ask.
If you did the same job and/or you see that my writing is incorrect please, comment, your input is much appreciated. This forum helped me a lot, I hope my post will help someone.