E53 Brake Booster and Master Cylinder DIY

[Sapphire68]

I searched high and low and never found any specific DIY for the E53 brake booster and master cylinder, so here is mine. This is specific to a 2006 E53 4.4i, left hand drive model (U.S.). I have about 98,000mi.

My symptoms were that when stopped and brake pedal pressed down normally, the car would creep forward slightly. I would have to press harder, basically to the floor, for the car to stay completely stopped. To me, this was a typical master cylinder problem or a "soft" pedal. It was not difficult to push the brake pedal, I just wasn't getting very good brake performance, more typical of a booster problem but without the "hard" pedal.

I had several issues to address so I am not completely sure what root cause was; however, my issues were nearly exactly those of the booster recall on the newer model X5's (I believe 2007-2010 models). Mine was not covered, though. First, my check-valve was shot. I confirmed this by disconnecting the vacuum hose from the vacuum pump to the brake booster (at the pump) and blowing into it. There was no resistance at all, confirming that the check valve was bad. If the check valve is good, you will not be able to blow into the booster through the hose. When I removed my master cylinder there was visible oil inside the brake booster - engine oil, not brake fluid. It was a rusty brown color and the large spring inside the booster was coated. This could also be confirmed through the grommet where the vacuum hose connects if you have one of those snake cameras with a light, without having to take the master cylinder off first. If you have oil in your booster then you will also likely need to address this at the vacuum pump with a rebuild (or new pump). I rebuilt mine a few months prior when doing valve cover gaskets, etc. so that had already been addressed. This is a very easy job with the correct o-rings, and there are several DIY’s on this around the forums.

Onto the work. Tools and parts needed:

Check Valve (for an E46) 34331160183 ($8.52) (optional)
Shark Bite ¾” to ½” barb connectors(local home improvement store, optional)
Heater/Coolant Hose, ¾” (optional)
Screw Clamps
Needle nose pliers
12mm combination wrench
13mm combination wrench
13mm ratchet with extensions
17mm combination wrench
Power bleeder (optional)
Philips screwdriver
Flathead screwdriver
Magnet/retriever tool
Upholstery/trim removal tool (pry tool)
Master cylinder bleeding kit (I used Dorman Help!) ~$10
Brake Booster 34336760461 ($290.05) (nuts and o-ring for master cylinder included with part)
Brake Master Cylinder 34316757743 ($129.66) (grommets and o-ring are included with part)
Brake Booster Seal 35111165132 ($4.84)
8mm Locking Nuts 07119905374 (x4) $0.48ea (you only need two, but I ordered extra and they came in handy)
Brake Fluid – DOT 4 (I use ATE)

The first thing I addressed was the check valve. The check valve for the E53 only comes integrated with the vacuum line to the pump, and I did not want to change the entire hose before figuring out all of my issues. So I spliced the E46 check valve into my brake line. I disconnected the “hard” line from the softer “J” shape just behind the aux fan.


The BMW parts are separated into two lines (11667629613 and 34336758560). These parts meet at the “J” that I refer to. I decided to cut the softer line and then cut/pry it away from the hard line. I could not pull the two apart. This method will leave the flare insert within the hard line and will make a great seal with the 3/4” heater hose.



The heater hose will then be a nice fit with the larger side of the check valve. The smaller side of the check valve connects straight into the “J” portion of the vacuum hose. Add in a few screw clamps and there are no vacuum leaks in the line (I confirmed with a vacuum gauge at various points along the vacuum line).


For reference, vacuum pump is at the top of this picture:


In my case, I also found another vacuum leak in the hose in another area, so I spliced in more of the heater hose to rectify that leak as well using the Shark Bite fittings. Alternatively, you could just replace the entire vacuum line with the integrated check valve (34336758560) for $53. If you plan to replace the entire line then I suggest removing the line first and replacing it as your last step to prevent the check valve from getting damaged. I like to use my upholstery pry tool to remove the check valve (and hose) from the brake booster. It gives good leverage without damaging the parts.

My vacuum pulls 28mmHg, and as I mentioned I checked this in several places along the vacuum line to find the additional leak and confirm that I had addressed all of the leaks. I have heard others say their vacuum pulls 23mmHg. I haven’t found a definitive answer on what is the proper range of the vacuum pump. The important thing is to measure it at the pump and confirm that it is the same at the booster.

Next, I recommend that you make some more space for removing and reinstalling your master cylinder and booster. Pull away the rubber weather strip on top of the fire wall just in front of the master cylinder reservoir. Remove the cover around the cabin air filter housing (you do not need to remove the air filter or its cover) by rotating the four connectors 90 degrees to disengage them. Remove the “air inlet tube” (the plastic part right next to the reservoir) by simply pulling it up and out. You will now have a clear view of the brake fluid reservoir and booster.


Remove the positive battery cable that is connected to the firewall just in front of the master cylinder using a 13mm ratchet. There is a plastic cover that will need to be removed, I used an upholstery pick tool to prevent damaging it. Push the cable out of the way and I recommend taping it to the fire wall away from where you will be working. Otherwise it will continue to flop into your way. Some will recommend that you disconnect the battery entirely, but for me that is just too much effort to access and remove the spare tire, gps antenna, etc. I usually wrap painters tape around the cable and tape it back then if it touches anything metal it won’t spark at you, or worse. There will also be another plastic piece on top of the bolt, remove this and keep these pieces together somewhere that you don’t forget. I left the bolt and front battery cable intact, but you can easily remove this if you prefer.

In order for there to be enough space for the booster to get in and out I found it to be a must to remove the windshield trim and windshield wiper arm. These only add a few minutes and give you a lot more space. Pop off the cover of the driver’s side (U.S.) windshield wiper. Using a 17mm combination wrench (ratcheting is convenient if you have one), remove the bolt from the wiper. Using the upholstery pry tool, pry the wiper up and off of the bolt. Lay it to the side.



Using your Philips screwdriver, unscrew the four plastic screws from the lower windshield trim which sits just underneath the wipers. I only loosed the four on the driver’s side to the middle of the car. Put a finger over the hole where the left-most screw was removed and pull the trim up. It will make a slight pop sound and then the plastic “rivet” should be removed and set aside with the plastic screws. If you pull up the trim without holding the rivet in place, it will pop out and it could disappear into the recesses of the engine compartment. Repeat for the next three. I just kept the trip up and out of the way without removing it completely.


Next, disconnect the wiper linkage arm for the driver’s side wiper by removing the 13mm nut where the arm connects to the motor. Free the linkage from the bolt and then you can move this arm out of the way. I had to play with the position of the other wiper to find the most room, which is pretty easy to just actuate (gently) the passenger wiper to move the linkage. I wasn’t confident that I could disconnect the ball joints and reconnect them, so I stayed away from that even though it would have provided some more space. You should now have plenty of space to work.



I stuffed a bunch of paper towels underneath the master cylinder and booster for two reasons: soak up the imminent brake fluid and catch parts and tools that you will surely drop. The space underneath the booster goes to the back side of the front wheel well, and it is a total pain to fish things out of there. You have to remove the trim behind the tire and some other things to access that space. Trust me, you just don’t want to drop stuff in there.

Remove the cap from the reservoir and lay it to the side. Suck out as much brake fluid from the reservoir as possible. I used a fluid hand pump that I use for doing ATF. My reservoir had a filter in it that I needed to pull out using needle nose pliers. I pumped into an empty milk jug. The sensor plug is easy to release, just push in on the tab and pull the plug out, then put the cap back onto the reservoir. Push the sensor wires out of the way, or tape them out of the way.

I found it best to disconnect the master cylinder from the booster before removing the brake lines from the master cylinder. This helped prevent some brake fluid spillage. Using your 13mm combination wrench, loosen (do not yet remove) the upper nut on the master cylinder (driver’s side nut). There is not a lot of space to turn here, so you will only get 1/8 of a turn each time. Just be patient. After a couple of full turns you can remove the nut with your fingers. I found it easiest to access the lower nut (passenger side nut) using a 13mm ratchet with short extension. Again, after a couple of full turns you can remove the nut with your fingers, but just loosen it for now. Move back to the upper nut and carefully remove it all the way. If you have a magnetic tool, put it in there close while you loosen the nut with your fingers. Do everything you can not to drop that nut. Repeat on the lower nut, again taking great care not to drop the nut.
Using your 12mm combination wrench, loosen the brake lines from the master cylinder. There are two connections, both are reasonably easy to access, but again you will only be able to make 1/8 to ¼ turns. Once loose, gently pull the lines out and away from the master cylinder. They are stiff but you can move them a fair amount without damaging them. With a lot of paper towels or towels within reach, pull the master cylinder off of the mounting bolts, up and out of the car. Take it immediately to somewhere that you don’t mind brake fluid spilling onto, and remember that if any drips on the car you need to clean it up immediately, otherwise it will strip the pain off your car. Put some tape over the brake lines to make sure nothing gets in them during the rest of your work.

So far, easy…right?

If you haven’t already, take a peek inside your booster to see what it looks like. If it’s clean, dry, and looks like new you might want to second guess your decision to change it, and do some more diagnostic work just to confirm that the booster is your problem. If you see oil or the color inside is orange, rusty, or brown then your booster needs to be replaced. If it’s not a problem yet, it will be soon. While doing this work, I took a peek inside my E46 which has ~140,000mi and the original booster. It was still clean and shiny like the new one I got.

Now it’s time to move inside the car. Get underneath the steering wheel and remove four Philips head screws from the foot control trim panel. There are also two plastic “locks” that need to be rotated 90 degrees and removed. The panel should drop out a little bit at which point you will need to disconnect the light and another plug-type thing (not sure what it is). Both are pretty easy and have some clips to press in for removal.
Looking up at the brake pedal you will see a small metal clip (circlip) holding the cross pin in between the pedal and the booster connector. Using a flathead screwdriver, pop the clip open and slide it either up or down until it releases from the cross pin. Push the cross pin out and the brake pedal is freed from the booster.

Following the booster rod, you will see two 13mm nuts at the supporting bracket. Using your ratchet and long extension, remove those nuts and the booster will be freed from the bracket.

Moving back into the engine bay, pull the booster toward the front of the car to free the bolts from the bracket, then you can pull the booster up and out of the bay through the space you made earlier. Keep an eye on the sensor wire so that you don’t rip it out or cut it. You will have to manipulate the brake lines out of the way during this part and this will be the point where you may still have some interference between the booster and the wiper linkage and it may require some manipulation of the wiper and/or the linkage to make more room. Pay attention to the orientation that works because that will be the easiest way to get the new booster into place. I found that you can push the brake lines to have some room to move towards and away from the fire wall without having to bend them.

When you open the new booster pay attention to any sounds you might hear. There shouldn’t be any sound of “loose parts” inside the booster. If there are, return it immediately to wherever you purchased it and get a new one. I went through this entire process just to find out that my brand new booster was defective from the factory and I had to do it all over. Don’t let this happen to you!

Put your new brake booster seal onto your new booster. It is a peel and stick and there is only one orientation. Put the new booster in with the same orientation that you got the old one out. You shouldn’t need to “force” anything; however, you may find it necessary to move the brake lines out of the way while you are getting the booster in. It is really helpful to have an extra set of hands here, if there is someone that can help you. You definitely don’t want to bend the lines too much or pound on the booster. When you have the correct alignment, the booster will almost fall right into place. I found it easiest to get the booster underneath the wiper linkage first, then fiddle with the brake lines to get it the rest of the way. The bolts will force the correct alignment into the bracket as long as you have it generally in the right way (vacuum line connects to the upper passenger side grommet).

Move back under the dashboard inside the car and loosely put on two of your new 13mm lock nuts, enough that they won’t come off on their own, but not too tight just yet. Reconnect the booster rod to the brake pedal by aligning the holes and pushing the cross pin back into place. Once you have the cross pin in a little bit, jiggle the brake pedal and push on the cross pin until it is fully across. Replace the circlip by aligning the hole on it with the cross pin, then sliding it down to lock it into place. At this point I place a pedal push rod (you could use a piece of wood or an extension tube from your shop vac) between the driver’s seat and the brake pedal. I place the push rod on the front edge of the driver’s seat and the other end on the brake pedal, then use the seat controls to actuate the seat forward so that it pushes the brake pedal. I will go back and forth a few times to look at the booster where the master cylinder will go. There is a “pin” that will start to become visible within the booster. This is the pin that pushes on the master cylinder to push the brake fluid to your calipers. You will notice on your master cylinder that there is a recess on the cylinder that will accept this pin. These MUST be lined up correctly when you install your master cylinder to your brake booster.

Get your master cylinder and place it into a vice (this process is the same whether you are putting in a new master cylinder or using your old one). If you are reusing your old one, make sure to replace the o-ring on it. One will come with your new brake booster. If you get a new master cylinder, it should also have a new o-ring already in place on it. The new master cylinders do not come with a reservoir so you will also need to remove the reservoir from the old one and put it onto the new one. The reservoir snaps into place on two “hooks” on the master cylinder. Pry the catches of the reservoir over these hooks and pull it off of the old master cylinder. This can be a little tedious and is easier with an extra set of hands because the master cylinder is tightly held on by the grommets. It is really easy to put the reservoir on the new master cylinder, which by the way, also comes with new grommets so you don’t need to order those. Remove the reservoir cap, but before putting any fluid in the master cylinder reservoir, connect the tubes and fittings from the master cylinder bleeding kit into the master cylinder.



Run the tubes into the reservoir and clip them to the opening so they don’t flop out when you start pushing the cylinder (there are clips in that kit if you feel so inclined). Fill the reservoir about 1/3 full with fluid so that the ends of the tubes are inside the fluid. Pump the cylinder about ten times listening to the sound it makes. At first, you will hear a lot of air and bubbles being pushed through the lines, and eventually that will be replaced with the sound of only fluid being pushed through the lines. That will be your indicator that your master cylinder is primed and ready to go. This process can also be completed using old brake lines or other things you have laying around, but I highly recommend doing it before you put it in the car; otherwise you will pump a bunch of air into your brake system the first few times you use your brakes. I leave this setup attached and then move the master cylinder from the vice into place in the engine bay. It shouldn’t drip much on the way over and will prevent air from getting in. The clips from the kit will hold the lines in place while you transfer it.
Remove the "packaging" cover over the cylinder and place the master cylinder into the brake booster. Make sure the pin inside the booster goes into the mating recess feature on the master cylinder. Push it on as far as you can without too much pressure, again reconfirming that the pin and the cylinder are aligned and engaged. You can push it on harder and actuate the cylinder but it will push fluid and it can get messy, plus the cylinder will reflex. Once I reconfirm proper engagement, I will go back to the driver’s seat and move it back an inch (allowing the push rod to move back a little bit), then go back to the master cylinder and make sure it is still aligned properly with the pin, push it on more, going back and forth until I can align the master cylinder with the mounting bolts on the brake booster and I can get the nuts on finger-tight to hold everything in place. I lost several nuts doing this and this is where the extras I ordered came in handy so I didn't have to waste time searching for them in the deep recesses of the wheel well.

You will have to battle the brake lines again here, but they are fairly easy to push out of the way while you push the master cylinder into place. Yes, this process can be a bit tedious and you can do it in a few seconds if you have a helper operate the driver’s seat while you keep pressure on the master cylinder. You can now return under the dash and tighten the 13mm lock nuts onto the booster bracket. You can replace the trim now or wait until later.

Moving back into the engine bay, tighten the 13mm nuts on the master cylinder. You haven’t removed the bleeder hoses yet right? Again, this can make the work a bit more tedious but leaving them on until you have everything tightened will spare you from getting more air into your system. You can also use this opportunity to bleed the master cylinder again using the brake pedal, just to make sure there is no air in there…and that the brake pedal is properly connected to the booster.

When you are ready to move on, remove the bleeder line on the side of the master cylinder and replace it with the brake line. Be careful not to cross-thread the brake line into the master cylinder. It should be fairly easy to engage the brake line nut with the master cylinder with your fingers at first. Move to the other brake line (the vertical one) and remove the bleeder line and replace it with the brake line. Once both lines are finger tight then you can tighten fully using the 12mm combination wrench. Deep breath, you’re almost finished with the hard stuff.

If you are putting in a new vacuum hose then now is the time to connect it to the system and plug the end of it (the check valve) into the brake booster. This is a really tight fit, so using the end of a socket is a pretty good way to push it in without hurting it. If you are using your existing vacuum hose, make sure before connecting it that your check valve is working by blowing through it (it should not allow you to blow towards the booster, and you should be able to blow towards the vacuum pump).

Refill your reservoir to the fill line with the proper brake fluid. Reconnect your wiper linkage to the motor (13mm nut). Replace your windshield trim with the four plastic rivets (push them into place) and then the plastic screws (these will not get tight, just put them in until they are fully threaded into place). Replace the wiper onto the spindle and tighten it using the 17mm nut (confirm alignment with other wiper). Replace the cap over the nut.

Now, you need to bleed your brakes, and I believe there are enough DIY’s on that out there. You will have air in your lines after replacing the master cylinder. If you aren’t getting any air out then it is stuck in there somewhere and you will likely feel it when you test drive. I was shocked at how much air was in my system, but again I had to do mine the equivalent of three times. I also was unable to use INPA or GT1 to do the ABS bleed due to either software or cable issues, and I needed to do that to get all of the air out. At the risk of scaring you away from doing this, I bled between 6 and 10 times at each caliper, going through liters of brake fluid to try to get all of the air out of my system, and it still wasn’t enough. I did the “activate the ABS on a dirt road” trick and still had air in the system. I ultimately had to take it to a shop to bleed using the correct software and even they had to do it three times to get the air out. Their assessment was that both the master cylinder and brake booster were bad. The master cylinder pushing air into the system and the brake booster not properly boosting (possibly torn diaphragm). They think this is why I had so much air in there.

Again, assuming you only have to do this once there is a good chance that you will introduce minimal air into your system, and that you will not get it into your ABS system. But, if you have INPA or GT1 and you can access the DSC/ABS module then you will be fine and you should be able to bleed/flush without any problems. Test drive in a safe place!

Total job time without bleeding is about 2 hours for me. Bleeding time is variable depending on how much air is in there. I’d say difficulty is about a 4 out of 10.

[lhordmclain]

Awesome write up!

[BMW-x5-48is]

I had to replace mines 2 years ago.. I remember it and will never forget.. driving down the bridge.. at the bottom red light and cars.. i press break pedal and car slides another 20 feet before stopping 3" inches from car infront of me... ohh i remember that day.... got the demm booster fixed ASAP!

[admranger]

Nice writeup. I just did this last weekend...

Couple of suggestions: On the wiper linkage, remove the wiper arms, then pull the two bolts (#2 in diagram) and nut (#4) and it all comes out easy peasy.

Also, install the master cylinder to the booster before installing the booster as it's much easier that trying to install it with the booster in place.

Oddly, my TRW booster shaft that connects to the brake pedal was a smidge too long and contacted the plastic trim piece. This small bit of contact caused havoc as it was enough to slightly activate the brakes, throwing multiple warning lights when I took the test drive. Took a few minutes to figure it out, but then I realized my brake lights were on all the time! What a pita... Quick zip with the vibratory saw and no more problem.

I used the INPA DIS software to activate the ABS/DSC system and bled 2 liters of fluid through the system to get the air out.

In hindsight, at 96k miles, I should have replaced the brake master cylinder when I replaced the booster. Using the DIS, you stroke the full length of the brake pedal travel 5 times at each corner. This is something you don't want to do as it can (and did in my case) scratch the MC seal, resulting in a slowly sinking brake pedal when you press and hold it... Oh well, another day maybe...

[admranger]

Lisle makes a windshield wiper puller tool (battery terminal puller) for little money.

[Junkycosmos]

crwarren11,

Very nice write up. Great details and $950 labor saved.
I went through similar with my booster
http://www.xoutpost.com/showthread.php?t=96360

Fully agree with your assessment that inside the booster should be perfectly clear and clean. My X5 with oil ruined booster only had a hint of oil residue in it but was fully trashed at 98k miles. While my E39 booster inside was brand new looking clean at 185k and still working great (looked in it when I changed mater in e39) now at 210k miles.

Clearly BMW has massive vacuum issues and broken 1 way valves on a lot of the 4.4/4.8 motors. Did you notice the replacement vacuum line now has a second 1 way valve in it.

I called BMW North America and registered the issue along with a formal complaint at dealer. Neither seemed to care much but facts on the safety recall still stand. I suppose we might never know why they did not include all 4.4/4.8 motors.

[Vicster]

Having same problem with my X5 4.4l it is a 2005 this is a very helpful write up and going to use after I order the parts. There is a big price differents in the aftermarket remanufactured ones to the oem. I am asking, if I am tight on funds is it a big deal to not buy the oem parts? I think I should buy the Booster & the Master cylinder & how do I know which one to buy? I am looking at Amazon not sure if Auto zone has in stock. Any suggestions for me.

[Sapphire68]

I would go with the oem parts but not genuine bmw. TRW makes the parts for bmw and you can get them from rmeuropean or other sources for good prices.

[Vicster]

I am having trouble after installing brake booster and master cylinder the peddle isn't going down. Any help please & What is this? - the INPA DIS software to activate the ABS/DSC system and bled 2 liters of fluid through the system to get the air out.

[Sapphire68]

Is the vacuum pump connected? Is the vacuum pump pulling good? Are you getting any brake power at all when you press the pedal? Did you put in a new check valve? Is it pointed in the right direction? Are any of the brake lines bent closed? Any difference with the car on or off?