2007, 4.8 N62 Brakes: master cylinder & booster
 

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 :rofl:

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. :cool:

Thanks for the write ups. Help to have this info for the DIY'ers. Did you replace the vaccuum hose from the booster to wherever that goes?

No, hose and valve are in good condition

I had the same issues, had it repaired under good will. There was recall on this back in 2013 (SIB 34 04 13, E70 Brake booster vacuum line). Two different TIS were issued, mine only had the first one done. I was able to press the issue since the updated TIS was not implemented.

Could replacing pads (the act of pushing the pistons back) damage the booster? I just finished the job and the pedal goes to the floor when the vehicle is ON, but I have a solid pedal when the vehicle is OFF. It didn't make sense for air to get in the lines on a simple pad replacement but I bled anyway. No effect.

As far as I understand the process, you don't push the piston back when you compress the pads. Piston is normally released by springs (they're inside) when you release your brake pedal.

So when you're compressing the pads you're just pushing the fluid out back to the tank through the previously opened piston valve.

Additional input for those who search later
 

I had the same brake issue and let me add a few comments.
. Brake booster test on youtube are inconclusive mine passed
. Experience told me I had a vacume pump,line or booster failure
. The easiest thing for me was to put a vacume gauge on line at booster read 25 inches knew I had booster failure.
. I also ordered mine from salvage yard be mindful between dis assembly at yard and shipping things can get out of order. On mine found master cylinder rod in wrong. Comparing new to old with a detail eye.
. I presure bled mine but still had poor peddle. I took it to a dirt road and activated the abs about 4 times in the dirt.
. I bled mine the old two man way with the engine off and it is now great
. Thanks for the great step by step

So, looks like I might need to replace my booster, but I want to check the line. Is the step above correct? I just pull (hard) the line straight out?

This is the type of hose connection.

Pulls out
 

It just pulls out. The ridges on plast hold it in rubber gromit

Thanks! Hate pulling on (especially plastic) parts that have not aged so gracefully. Finding big chunks of the engine partition in the bay was kind of a big letdown, but that didn't stop me...

I ended up getting a used booster off of ebay based on many other threads/experiences and dissected the inside of my old one - it was in very bad shape compared to the 'new' one.

The one I purchased was from 2011, same part number and fits perfect, however, the brake pedal doesn't want to firm up and there's a different kind of air noise than before.

Here is the story so far:

1. Watching LTFT's started noticing a change ~3.5 ish numbers on the negative side; bank 1 slightly higher (vacuum pump tie - in?). Started trying to find some sort of vacuum leak or unmetered air or something to explain this anomaly. Found nothing, but a tiny oil leak from one of the driver's side sensors - not sure if it's the seal or just not tight enough (yet to resolve)

2. Started hearing a strange whooshing sound (like when you blow up a balloon the old fashion way). Tracked it down to the booster.

3. Went ahead and picked up a used one, just in case - kept trying to research...

4. Changed booster - problem went away, inside of old one looked horrible compared to 'new' one.

5. Bled brakes with air/vacuum - did NOT use any software.

6. Brake pedal won't hold firmness, brakes do work fine, just at the very bottom of the pedal. No fluid leaks that I can find anywhere, none existed before.

7. I pulled the booster back out, smoke tested it - smoke came out the air filter section - the part that extends to the pedal and covered by shield with a dust cover (?), which extends from the diaphragm plate. Hope that explains it. <-- Not sure if this is normal or not since this is where the booster gets atmospheric pressure.

8. Next steps, use ISTA to activate ABS when bleeding...?

Not sure what may be the actual issue here, looking for thoughts/advice/experience. Also, the booster I bought does have a 6 month warranty, so no worries there if it's actually bad.