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fredgus 11-18-2012 07:12 AM

Leaking brake connections
I am suddenly losing brake fluid - It seems to be leaking out of the connections on the top of the master cylinder - see picture. What needs to be replaced or tightened here? Has anyone else had this happen?

robertobaggio20 11-18-2012 08:42 AM

That's your brake master cylinder. The brake booster (the large round thing behind it) is connected to the driver's brake pedal. Your foot's force is amplified by the brake booster and directed to the brake master cylinder, which squeezes the reservoir of brake fluid that it retains, through the metal brake lines which lead to the callipers at all four wheels. This arrangement is done to increase hydraulic pressure on the brake fluid to ensure maximum clamping force is made available at the callipers, which resulted in the E34 breaking world 60-0 stopping records in the early 90s. Pardon me, I had to brag a little.

It appears that part #2 in the diagram below may be defective :

The diagram is deceptive : there are 2 units of part #2. You can try changing both to see if that helps.

If its the nuts which screw into them which are, well, screwed, then you have to change the entire brake fluid reservoir to which they are connected to. The diagram shows that they are not a separate part of the thing. I wouldn't advise a diy workaround on this even if it was possible, as we are dealing with very high pressures and this is a literally a driving safety issue.

That said, this is a very obscure problem that you've encountered. If you need to change the brake lines/brake reservoir, I will wager that a good used unit will do fine.

You ought to inspect everything including the brake booster : ensure that you do not have other brake related issues.

Until you have taken care of this, please do not drive at highway speeds, and keep way more distance between yourself and the car in front than you normally would. Check and top up oil before each trip that you have to make. It is best of course that you get this sorted out at a workshop bright and early on monday morning. Sometimes there's no way to avoid the expense.

If its just a brake reservoir replacement affair, it should take a professional around 30 minutes and 1 litre of dot4 oil to sort it out. However, if you need to change your brake master pump, only buy new and of the correct brand (lucas or girling) according to your car's chassis number (or just use what is already in there). For some reason, the brake master pump and the brake booster need to be of the same brand even if the part numbers for different brands are the same, if not everything gets off. Costly lesson I learned.

The brake booster may involve around 20 minutes of work to swop out for someone who has done this before.


fredgus 11-18-2012 04:08 PM

Wow, thanks Roberto! Very complete reply and extremely helpful. Is replacing those plugs as simple as it looks?

robertobaggio20 11-18-2012 06:22 PM


Originally Posted by fredgus (Post 7201912)
Wow, thanks Roberto! Very complete reply and extremely helpful. Is replacing those plugs as simple as it looks?

I have no idea, have not seen it done before. There are others here who are more experienced with this.

I would hazard a guess that it can be done if the space is accessible, and considering the situation its in right now it probably would not matter if you damaged it further, but you must take great care not to damage the oil lines by uncontrolled movement of your wrench.

Please check the bentley manual for any relevant directions.

Hmmmmm.......hmmmmmm.........hmmmmmmmmm..........I 've just got a wild idea. Dude, are you willing to give this a shot ? Just to see if it works. Probably too ugly, and the parts and repair are probably too cheap/doable to keep it this way. Just to satisfy my curiosity, and since you already have an issue and since this will only take 10 minutes.

1. Shut down the car for the day/night.
2. Clean the brake master pump area with a damp tissue filled with carb cleaner, degreaser or water, as best as you can. Do not spray water or carb cleaner directly at it as it may enter the brake master pump
3. Blow air forcefully using a any flexible hose or straw onto the area to clear it of dust as best as you can.
4. Get a tube of clear high temp rtv silicone window sealant. It should be usable for glass, acquariums, radiators...these are the pictures you might find on the carton. Apply it to the area. Dab gently with your finger, but not in such a way that you force sealant into the leaking spaces.
5. It cures enough to seal within 30 minutes but its best to leave it for a couple of hours.
6. The next day, top up fluid into the brake fluid reservoir.
7. Drive normally, paying heed to the safety pointers I've mentioned earlier. Test your brakes variably when it is safe to do so.
8. Check on the leak whenever you finish a trip.
9. Have a portable light with you.

These should not involve additional costs on your end as you should have carb cleaner and clear high temp (not gasket temp levels) rtv silicone sealant anyway for on the spot repairs and other purposes.

An adaptation of the above worked for my radiator's busted bleed screw fantastically. It withstood pressure while driving with no hint of rupture. I am curious to see if it seals the gap and withstands the brake master pump's pressure as well.

It should, in any case, not make anything worse than it already is. The sealant does not flow and would not ooze into the leak's spaces naturally if you don't force it in. The dried sealant is quite easily removed using a screwdriver and does not rupture sealed surfaces the way removing glue might.

If you do this, please put a spot of the sealant in another part of the engine bay. The next day, after it has dried, put one drop of brake fluid onto it. Look at it a few hours later and see if there is any material deterioration. Dab it with your finger to feel the texture, and then dab the dry sealant that you applied around the brake master pump's lines to see if there is any difference.

Please post your observed results here for everything that I've mentioned.

If it works, this could be a useful on-the-spot quick and dirty fix for general use, and would be a good contribution to our response regime for issues.

And even if this works and lasts a few days with no apparent deterioration, please carry out the correct repair soon and drive conservatively until then. These are brakes.....failure could lead to death for the innocent.


fredgus 11-18-2012 07:04 PM

Huh, that is an interesting idea. . . I clean them up tomorrow morning and pick up some sealant while I'm out looking for parts. That buys me a few days to work on the repair, too. I'll top up the fluid and stay at safe distinces in town for a few days and see what happens. Could be a good "field repair", but I'm with you, needs to be done right, and soon. I typically have two youngs kids with me and there are countless other people I don't want to hurt either! :-)

fredgus 11-18-2012 07:27 PM

I don't know it it going to work. The fittings are just weeping fluid. Everytime I cleaned them off they were immidiately wet with brake fluid again . . . I'll see what it looks like in the morning, but I may just have to go right to the real fix for want of a dry surface.

robertobaggio20 11-18-2012 08:07 PM


Originally Posted by fredgus (Post 7202221)
I don't know it it going to work. The fittings are just weeping fluid. Everytime I cleaned them off they were immidiately wet with brake fluid again . . . I'll see what it looks like in the morning, but I may just have to go right to the real fix for want of a dry surface.

If you stop filling the reservoir, they will stop weeping fluid eventually. Try cleaning it up after you've let the car set down for a few hours without driving and see if it stops long enough for the sealant experiment.

BMWFatherFigure 11-19-2012 09:28 AM

Those fittings are unpressurised fluid supply. They seal with an 'O'ring. From memory the 'hex' area is cast into the cylinder and does not rotate or lock down the inlet tubes. If those seals have gone I would remove and overhaul the complete cylinder. IMO don't use any sealant to fix the leak, replace the aged seals. Here the parts from a brake shop would be about $30 for a complete kit.

fredgus 11-20-2012 07:47 PM

I ended up just doing the repair. The local stealership was able to get the parts pretty quick - $7.75 for each rubber grommet. I skipped the sealant experiment for 2 reasons, first everything was so coated and inundated with brake fluid that there was nothing for any sealant to stick to. Second (prehaps more important) the rubber grommets that were there were falling apart (therefore leaking) so completely that I feared that I would end up with sealant in my brake system, not a good thing.

The "hex" portions in the picture are actually rubber! That is the top of the grommet that the lines from the brake fluid resevoir plug into. There are no fateners at all. In fact, the repair was so simple and easy that I was convinced that I had done something wrong, but no leaks so far! All that needed to be done was to pull the lines out, then pull out the rubber grommets, then push in the new grommets (which are simply round on top, no fancy "hex" shape), then push in the lines and top up the fluid.

I did fill the holes that the lines plugged into with fluid before I pushed the lines back in to keep from forcing air into the system.

My gut feeling on this is that the 18 year old rubber had just absorbed too much brake fluid (nasty stuff) and was falling apart. The new rubber felt firm and holds the lines in tightly. The old rubber felt like a really wet sponge, and allowed the lines to move quite a bit. I would say that this is worth looking at on many E34s. It was any easy fix, and could help avoid disaster.

2 little things - I did spill quite a bit of fluid on the painted surfaces inside the engine compartment, right above the lights, when I pulled the first plug. I cleaned it off quickly, but that paint will never be the same, and I will have to watch it for rust issues from now on. The second plug I was more careful with and only added to the brake fluid mess that was already there from the leak. Also, at least on my 530, the overflow line from the radiator runs right past where you will be pulling and pushing to get the lines out and back in. I snapped that baby in two when my hand slipped. A clean break that can be patched with a little fuel line for now, but that plastic is as old as the rubber that is being replaced and is very brittle.

Thanks for the advice and links!

robertobaggio20 11-20-2012 08:50 PM

I'm going to change my brake master pump's grommets immediately. Good show dude. :)

In the finest tradition of the fest, you must now go on a WOT run (wide open throttle), with your windows wound down even if though its winter (well on that we can compromise if you like :) ), and come back and have a can of cold german ale. :)

p.s. There's a quick and dirty solution to the stripped paint. Just recoat it with black spray paint. Does not need to be high temp spray paint. If you are concerned that you will get paint everywhere, spray it into a piece of paper, such that it forms a puddle of paint (will dry within 2 minutes), dab it with a tiny paintbrush and paint over the stripped surfaces directly. No more rust issues. I use this for little nicks on my bumper and paintwork whenever I need to.

BMWFatherFigure 11-21-2012 03:09 AM

Brake fluid is hygroscopic so a water flush will remove it all.

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