A couple weeks ago, I had some serious brake malfunction after some rain and a carwash. Thanks to the fine members of this forum, it was deduced that the compartment where the booster is located had filled with water, and water was sucked into the booster as a result. For those who don't know, the booster basically is an circular container with a diaphragm in the middle. Engine vacuum lowers the pressure on the master cylinder side of this diaphragm to assist the driver pushing the brake pedal down. When it filled with water, I think some water even got sucked into the vacuum lines to the engine. An old thread I found was detailing one members experience with this issue, where enough water was sucked into his engine to cause hydrolock and enough damage to cause his insurance to buy a new engine!
Needless to say, this is a potentially serious problem and it all has to do with the drain hole in the bottom of this compartment getting clogged with debris (not even big debris either!) and filling up with water. It only takes a few minutes to access this compartment, and although the drain hole is obscured by the booster you can at least reach down there and try to get stuff out of there or check if any water is accumulating. Now, onto the actual DIY:
PARTS NEEDED: Brake Booster (P/n 34331165541), Booster gasket (p/n 35111165132), master cylinder o-ring (p/n 34311165092), 1-2 pints DOT4 brake fluid
For the booster you can either get the BMW branded one for like $600 or Pelican has a TRW Lucas branded one (exact same unit) for $330. I opted for the cheaper one.
First thing you're going to want to do is remove the driver's side cabin air filter and filter housing. When you do that, this is what you'll see:
As you can see, underneath the filter housing there's this compartment where the booster and brake master cylinder sit. In my case this filled with water probably both due to rain we got, and after the carwash it filled up enough so as to suck water into the booster somehow, and probably into the vacuum line as my car died while idling and braking right after the wash and a couple times after.
Anyway, first thing you'll want to do is remove the cap to the tank along with the brake fluid level sensor harness. Then, remove the brake fluid from the expansion tank/reservoir using some sort of vacuum deal. I suppose a turkey baster would work here too. Theres a filter deal down in the expansion tank too that prevents you from getting all of the fluid out, but try to get as much as you can out, as it prevents it from coming out later.
Notice also that the tank is divided; there is another small section where the clutch slave line attaches. The fluid in there cant be removed until you remove the line to the clutch, and then it'll just fall out. I had trouble getting the clutch line out, and found that I had to cut s small notch in the end so it was wide enough to clear the flange deal at the end of the plastic protrusion on the expansion tank it hooks up to. You can see what I mean here:
Now that the clutch line is removed, you have to remove the expansion tank. There is a line running out of it that attaches to a hydralic line you have to pull off, but once you do that you can reach under the master clynder and unhook the two plastic latches on either side of the master cylinder, once you do that tilt the tank away from the engine and pull and it'll pop out of the master cylinder. I still had some brake fluid in there so it would be wise to put some shop towels underneath to catch. Worst case is it'll drip down into the compartment where you can clean it up later. Here's the master cylinder with the tank removed and the tank sitting out of the car, you can see the hose coming out of the bottom that I was talking about is circled:
Next you have to remove some cover pieces, first one snaps off above the divider deal (its removed and was where the red circle is) where the brake lines and vacuum line head toward the engine, and the second one that is below the wipers you unscrew the one screw and lift it out:
Next you can pul out the vacuum line from the booster, it'll just pop out. Now comes the fun part. Before you can take the booster and master cylinder out you have to unscrew the two brake lines on the other side of that divider deal. There isn't much clearance, but I managed to get two wrenches on there. Hold the big middle coupling steady as you unscrew the fitting on either side. I found that a normal wrench wanted to strip the fittings, so I used those wrenches that are shaped like a nut. The fitting size is 11mm and the the middle coupling is 15mm. The last thing you want to do is strip these hydraulic lines, so please be careful.
Once they are out, you can remove the brake lines from the master cylinder. These come off rather easily. Here's a shot of the master cylinder/booster with all the brake lines removed:
It's worth noting that the TIS calls for you to seal the brake lines and master cylinder openings so as to prevent dirt from entering. I used duct tape for this purpose, and just used care overall to prevent that from happening.
Next you have to go into the drivers footwell and remove the trim piece above the pedals. There are three screws and another fastener deal that you just turn a quarter turn to undo. You can then lift the panel down, and you'll see the wires that attach to the gong, which can be removed:
The trim panel then comes out, and you'll see the other end of the brake booster. The TIS calls for you to remove the brake light switch (circled in green), which I did but I'm not totally sure if it was necessary. It's very easy to remove though, it just slides out. Then you have to disconnect the clip (circled in red) that keeps the pin coming from the brake pedal attached to the booster:
The TIS also calls for you to undo the recoil spring from the brake pedal, but I found that to be difficult and not needed. Now you have a clear shot at the two nuts that hold the booster in place (circled). You can see them along with the pin to the booster and the retaining clip removed. To remove these two nuts you'll need a deep socket rachet and patience. I found for the top one you I only had clearance to turn the wratchet about an inch, so it took a while:
Now the booster comes out pretty easily. Take care not to bang around the master cylinder or anything and not to damage any brake lines but it basically just slides right out. As you can see below, the drain hole in my compartment was quite full of sludge, and you can't even see the drain hole:
All clean, now you can see the drain hole:
Now you can unscrew and remove the master cylinder from the old booster.
When I removed the booster, it was FULL of water. Not just clean water either, but dirty sludgy water. I didn't get a shot of me pouring it out of the old booster, but here's a picture of some that got on the ground. The yellow stuff is the brake fluid, and the black oil looking fluid next to it is the some of the water that came out of the booster! Also, I got a shot of the inside of the booster, which as you can see was disgusting:
When the master cylinder is removed, replace the oring and reinstall into the new booster. Torque the nuts to 26Nm, and put on the new gasket. Here's the new booster with master cylinder attached:
From here, it's just a matter of putting everything back together in reverse order. The brake lines are suppose to be torqued to 18Nm, but I don't know how one could use a torque wrench to do it so just tighten them fairly tight but don't overdo it. Again, use care not to get any dirt into the lines or master cylinder during reassembly. I found that putting everything back together took half the time as taking it all apart.
Once everything is back together, you have to refill the expansion tank with new DOT4 fluid and bleed the brakes. Although one is supposed to use the GT1 near the end of the bleeding process to cycle the DSC/ABS pumps, I didn't have one so I suppose I missed out on cycling the old fluid out of those. Hopefully it's not too big of a deal.
I'm totally not mechanically talented, and this is easily the most complicated thing I've ever attempted on a car. As it required a special tools and a lift to bleed the brakes, I ended up doing all the work at a place called First Gear Garage, located in Eden Prairie, MN. They've been open for like 7 or 8 months, and you basically rent out a bay or a lift by the hour. They provide you with tools and everything to get the job done. It's a very cool, clean shop and I wouldn't have attempted it out of the garage at home. Serious props to these guys!
Here's a couple shots of the shop. They were actually doing a free brake clinic today where they teach you how to maintain your brake system, replace pads, bleed, etc. It's cool concept for a business. Here's a couple shots of the garage and clinic in progress:
Like I said, if I can do this than anyone can do this. I don't have much experience at all, but with the proper tools and some common sense I got it done. My brakes are so much better now, even better than before the booster became flooded with water. If you have any comments/questions please let me know.
Needless to say, this is a potentially serious problem and it all has to do with the drain hole in the bottom of this compartment getting clogged with debris (not even big debris either!) and filling up with water. It only takes a few minutes to access this compartment, and although the drain hole is obscured by the booster you can at least reach down there and try to get stuff out of there or check if any water is accumulating. Now, onto the actual DIY:
PARTS NEEDED: Brake Booster (P/n 34331165541), Booster gasket (p/n 35111165132), master cylinder o-ring (p/n 34311165092), 1-2 pints DOT4 brake fluid
For the booster you can either get the BMW branded one for like $600 or Pelican has a TRW Lucas branded one (exact same unit) for $330. I opted for the cheaper one.
First thing you're going to want to do is remove the driver's side cabin air filter and filter housing. When you do that, this is what you'll see:
As you can see, underneath the filter housing there's this compartment where the booster and brake master cylinder sit. In my case this filled with water probably both due to rain we got, and after the carwash it filled up enough so as to suck water into the booster somehow, and probably into the vacuum line as my car died while idling and braking right after the wash and a couple times after.
Anyway, first thing you'll want to do is remove the cap to the tank along with the brake fluid level sensor harness. Then, remove the brake fluid from the expansion tank/reservoir using some sort of vacuum deal. I suppose a turkey baster would work here too. Theres a filter deal down in the expansion tank too that prevents you from getting all of the fluid out, but try to get as much as you can out, as it prevents it from coming out later.
Notice also that the tank is divided; there is another small section where the clutch slave line attaches. The fluid in there cant be removed until you remove the line to the clutch, and then it'll just fall out. I had trouble getting the clutch line out, and found that I had to cut s small notch in the end so it was wide enough to clear the flange deal at the end of the plastic protrusion on the expansion tank it hooks up to. You can see what I mean here:
Now that the clutch line is removed, you have to remove the expansion tank. There is a line running out of it that attaches to a hydralic line you have to pull off, but once you do that you can reach under the master clynder and unhook the two plastic latches on either side of the master cylinder, once you do that tilt the tank away from the engine and pull and it'll pop out of the master cylinder. I still had some brake fluid in there so it would be wise to put some shop towels underneath to catch. Worst case is it'll drip down into the compartment where you can clean it up later. Here's the master cylinder with the tank removed and the tank sitting out of the car, you can see the hose coming out of the bottom that I was talking about is circled:
Next you have to remove some cover pieces, first one snaps off above the divider deal (its removed and was where the red circle is) where the brake lines and vacuum line head toward the engine, and the second one that is below the wipers you unscrew the one screw and lift it out:
Next you can pul out the vacuum line from the booster, it'll just pop out. Now comes the fun part. Before you can take the booster and master cylinder out you have to unscrew the two brake lines on the other side of that divider deal. There isn't much clearance, but I managed to get two wrenches on there. Hold the big middle coupling steady as you unscrew the fitting on either side. I found that a normal wrench wanted to strip the fittings, so I used those wrenches that are shaped like a nut. The fitting size is 11mm and the the middle coupling is 15mm. The last thing you want to do is strip these hydraulic lines, so please be careful.
Once they are out, you can remove the brake lines from the master cylinder. These come off rather easily. Here's a shot of the master cylinder/booster with all the brake lines removed:
It's worth noting that the TIS calls for you to seal the brake lines and master cylinder openings so as to prevent dirt from entering. I used duct tape for this purpose, and just used care overall to prevent that from happening.
Next you have to go into the drivers footwell and remove the trim piece above the pedals. There are three screws and another fastener deal that you just turn a quarter turn to undo. You can then lift the panel down, and you'll see the wires that attach to the gong, which can be removed:
The trim panel then comes out, and you'll see the other end of the brake booster. The TIS calls for you to remove the brake light switch (circled in green), which I did but I'm not totally sure if it was necessary. It's very easy to remove though, it just slides out. Then you have to disconnect the clip (circled in red) that keeps the pin coming from the brake pedal attached to the booster:
The TIS also calls for you to undo the recoil spring from the brake pedal, but I found that to be difficult and not needed. Now you have a clear shot at the two nuts that hold the booster in place (circled). You can see them along with the pin to the booster and the retaining clip removed. To remove these two nuts you'll need a deep socket rachet and patience. I found for the top one you I only had clearance to turn the wratchet about an inch, so it took a while:
Now the booster comes out pretty easily. Take care not to bang around the master cylinder or anything and not to damage any brake lines but it basically just slides right out. As you can see below, the drain hole in my compartment was quite full of sludge, and you can't even see the drain hole:
All clean, now you can see the drain hole:
Now you can unscrew and remove the master cylinder from the old booster.
When I removed the booster, it was FULL of water. Not just clean water either, but dirty sludgy water. I didn't get a shot of me pouring it out of the old booster, but here's a picture of some that got on the ground. The yellow stuff is the brake fluid, and the black oil looking fluid next to it is the some of the water that came out of the booster! Also, I got a shot of the inside of the booster, which as you can see was disgusting:
When the master cylinder is removed, replace the oring and reinstall into the new booster. Torque the nuts to 26Nm, and put on the new gasket. Here's the new booster with master cylinder attached:
From here, it's just a matter of putting everything back together in reverse order. The brake lines are suppose to be torqued to 18Nm, but I don't know how one could use a torque wrench to do it so just tighten them fairly tight but don't overdo it. Again, use care not to get any dirt into the lines or master cylinder during reassembly. I found that putting everything back together took half the time as taking it all apart.
Once everything is back together, you have to refill the expansion tank with new DOT4 fluid and bleed the brakes. Although one is supposed to use the GT1 near the end of the bleeding process to cycle the DSC/ABS pumps, I didn't have one so I suppose I missed out on cycling the old fluid out of those. Hopefully it's not too big of a deal.
I'm totally not mechanically talented, and this is easily the most complicated thing I've ever attempted on a car. As it required a special tools and a lift to bleed the brakes, I ended up doing all the work at a place called First Gear Garage, located in Eden Prairie, MN. They've been open for like 7 or 8 months, and you basically rent out a bay or a lift by the hour. They provide you with tools and everything to get the job done. It's a very cool, clean shop and I wouldn't have attempted it out of the garage at home. Serious props to these guys!
Here's a couple shots of the shop. They were actually doing a free brake clinic today where they teach you how to maintain your brake system, replace pads, bleed, etc. It's cool concept for a business. Here's a couple shots of the garage and clinic in progress:
Like I said, if I can do this than anyone can do this. I don't have much experience at all, but with the proper tools and some common sense I got it done. My brakes are so much better now, even better than before the booster became flooded with water. If you have any comments/questions please let me know.