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Discussion Starter · #1 ·
Searched, and didn't see a single thread on this.

Basically, went out to the car this morning (32*F / 0*C ambient temp). Started her up. Stepped on the brakes, and nothing. Pedal locked in full upright position. Adding moderate pressure did nothing. No pedal movement what so ever. No brakes what so ever. Nada, zilch, zero.

Really glad this happened at groundspeed zero, and not say, on the highway!

Called up local BMW dealer, they gave me the bird: "Car is out of warrantee.. sorry. You pay for repairs." Contacted BMWNA, waiting for response.

Any ideas guys?

Seems as though I'll probably end up fixing this myself and filing suit agains BMW if they piss in my face.
 

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Searched, and didn't see a single thread on this.

Basically, went out to the car this morning (32*F / 0*C ambient temp). Started her up. Stepped on the brakes, and nothing. Pedal locked in full upright position. Adding moderate pressure did nothing. No pedal movement what so ever. No brakes what so ever. Nada, zilch, zero.

Really glad this happened at groundspeed zero, and not say, on the highway!

Called up local BMW dealer, they gave me the bird: "Car is out of warrantee.. sorry. You pay for repairs." Contacted BMWNA, waiting for response.

Any ideas guys?

Seems as though I'll probably end up fixing this myself and filing suit agains BMW if they piss in my face.
Possible condensation freezing, preventing the fluid from being pushed? See what happens after it warms up after being in the sun.

Regards,
Jerry
 

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i highly doubt the freezing point of brake fluid is below the temps in NYC this time of year.

sounds like some component used to compress the fluid is seized...i.e brake booster as vantaam5 says
 

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i highly doubt the freezing point of brake fluid is below the temps in NYC this time of year.

sounds like some component used to compress the fluid is seized...i.e brake booster as vantaam5 says
I think he may mean condensation or water mixed in with the fluid or potentially in the booster and then freezing, not the fluid itself freezing
 
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i highly doubt the freezing point of brake fluid is below the temps in NYC this time of year.

sounds like some component used to compress the fluid is seized...i.e brake booster as vantaam5 says
vantaam5 may be right (he often is!), I was suggesting that if there was condensation (water) in the brake lines, it could have frozen. If the temps come up and ice unfreezes back to water, then the problem is not mechanical. If the temps come up and no change, then yes, brake booster is possisble, although even without the booster I would think there would be SOME brake action.
Regards,
Jerry
 

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Maybe you can try unloose on of the bleeding screws(brake calibers) and see what happens. If after that pedal is moving try it all calibers and you will find out what caliber/house is frozen.
It is only thing what comes up in my head :)
 

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Discussion Starter · #9 ·
Thanks everyone for the quick replies. I take it this hasn't happened to anyone here firsthand. I've had the car "defrosting" in my garage for two hours, gonna go out and check it after I finish this.

Most likely your brake booster is full of water(because drain hole underneath clogged) and the water in there froze.
It sounds to me like something to this effect. I have unclogged the drain hole so I'm doubting I'll find water in there (will check though). Luckily those parts are relatively cheap, and I have yet to bleed and replace brake fluid. I did all other fluids already but that :(

No matter what, I'll keep this documented on here. Should be some good info and definitely a safety matter!
 

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Most likely your brake booster is full of water(because drain hole underneath clogged) and the water in there froze.
Bingo!

Water anywhere other than inside the booster will not lock the pedal at the fully extended
position. To test; with brake pedal rigid as described before starting the engine, hold down
the brake pedal and then start the engine. If the booster is not frozen up, the pedal will
drop at least halfway to the floor. But I'll bet it doesn't move.

Regards,
Alan
 

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Discussion Starter · #11 ·
Bingo!

Water anywhere other than inside the booster will not lock the pedal at the fully extended
position. To test; with brake pedal rigid as described before starting the engine, hold down
the brake pedal and then start the engine. If the booster is not frozen up, the pedal will
drop at least halfway to the floor. But I'll bet it doesn't move.

Regards,
Alan
Alan,

Your right. No drop like you would get after ignition with a properly functioning brake booster. After thawing out the car in the garage for 3 hours, the pedal has about 1-2" of play now. It is slowly freeing up. I'd bet if I left a heat gun on the booster, the pedal would return to normal.

Now, the obvious question, how do I get the water out of the booster? Bleed the brakes I'd assume? We havn't had rain in days, so I'm guessing this water has been trapped in there somehow for a while. But I still don't understand how it got in there in the first place. If you could elaborate on this, I'd appreciate it a whole lot!
 

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replace the booster. it's simply a large vacuum diaphragm, it is completely separate from the brake fluid.

for the future: make sure to remove your cabin filters semi-annually and remove debris.
 

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Alan,

Your right. No drop like you would get after ignition with a properly functioning brake booster.
After thawing out the car in the garage for 3 hours, the pedal has about 1-2" of play
now. It is slowly freeing up.
I'd bet if I left a heat gun on the booster, the pedal would
return to normal.

Now, the obvious question, how do I get the water out of the booster? Bleed the brakes I'd
assume? We havn't had rain in days, so I'm guessing this water has been trapped in there
somehow for a while. But I still don't understand how it got in there in the first place. If you
could elaborate on this, I'd appreciate it a whole lot!
Brake bleeding will not remedy the problem, since the water is not in the hydraulic system.
The compartment where the booster and master cylinder reside has a drain port in the aft,
inside corner and gets plugged by debris. In turn, the booster has a vent hole in the bottom
of the casing. Water floods the compartment due to blocked drain and then gets into the
booster through it vent port.

You need to use compressed air, blown in around the aft, inside corner of the compartment.
This will move the debris toward the outside so that you can fish it all out.

Hopefully, your booster will return to normal, but I suspect this may have been going on for
some time. If true, the diaphragm housing is likely corroded and there is a thick gooey mess
inside. If it were mine, I would replace the booster and master cylinder together.

If you do replace them, be sure you have the brakes bled using a GT1 or equivalent, due to
air will be trapped upstream of the ABS/DSC hydraulic unit. It is impossible to remove except
by activating the modules high pressure pump and then cycling the various control valves.
DO NOT allow yourself to persuaded by any repair facility that it's not needed. If they try,
go elsewhere, because are incompetent.

Regards,
Alan
 

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If true, the diaphragm housing is likely corroded and there is a thick gooey mess
inside. If it were mine, I would replace the booster and master cylinder together.
I was thinking the same thing. Even if the water is removed, I would be concerned about corrosion of metal components. I'd replace the unit. In the future instead of freezing up from the cold, it could be from rust.
 

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I'm not sure why no one is pointing to the master cylinder itself. As mentioned the vaccuum assist is a large diaphragm. How would ohh, 30cc of water condense in there, enough to prevent the diaphragm from moving? That's probably the volume of water that would have to ice up the 8 inch diameter diaphragm (plus/minus). With loss of vaccuum the pin at end of brake arm still makes mechanical contact with the master cylinder preventing loss of all braking. More likely is particulate material in the master cylinder and with heating and pressure it may be dislodged for now. Millions of cars have this system and failure such as this is rare. Now, I had failure on my E28 however and BMW (and Audi before them) learned really quickly not to use hydraulic assisted brakes since this is the type of failure one gets. I remember not being able to press down the brake with any degree of force coming down a hill at 35 mph. Now try sweating that!
 

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I'm not sure why no one is pointing to the master cylinder itself. As mentioned the vaccuum assist
is a large diaphragm. How would ohh, 30cc of water condense in there, enough to prevent the diaphragm
from moving? That's probably the volume of water that would have to ice up the 8 inch diameter diaphragm
(plus/minus). With loss of vaccuum the pin at end of brake arm still makes mechanical contact with the master
cylinder preventing loss of all braking. More likely is particulate material in the master cylinder and with heating
and pressure it may be dislodged for now. Millions of cars have this system and failure such as this is rare. Now,
I had failure on my E28 however and BMW (and Audi before them) learned really quickly not to use hydraulic
assisted brakes since this is the type of failure one gets. I remember not being able to press down the brake
with any degree of force coming down a hill at 35 mph. Now try sweating that!
The water is not condensing inside the booster, it floods the booster through the vent port if the compartment
drain is plugged and then subsequently fills with water. If the booster was not at fault, the brake pedal would
have dropped when held during engine start. The OP has already confirmed that it did not.

Regards,
Alan
 

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Discussion Starter · #18 ·
Guys, seems like a flush would do the trick. I'm guessing frozen fluid in the lines as well.

*We havn't had heavy rain in a while
*The car sat in a garage for 2 weeks during a phase of preventative MX I was completing
*The drain hole, which I did find to be clogged during the fall, has been cleared since then and the car has been driven regularly.

I don't think water recently found its way into the master cylinder or the booster, but I'd say it is possible in the past it mixed itself with the brake fluid over time. In theory, flushing the system should cure this. There is a small possibilty of corrosion to the master cylinder or booster, but I would doubt this as the mix of water and fluid should prevent any corrosion.

I'm guessing my best course of action would be to flush the fluid out and then see if the problem returns after leaving the car in sub-zero temps for an extended period. Anyone concur?
 

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Fingers crossed you get it sorted out, but I'm confused as to why you think BMW should pay for it when at the least your car is seven years old and out of warranty?

cheers
 

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If a line would freeze,the pedal would still have travel.

And if there is so much moisture in there that it freezes,the pedal would have stayed on the floor already before on repeated harder braking.
Flushing the system will not cure the issue.

The water from the clogged drain hole(as confirmed)that was flooding the booster for a long time just froze up now with the low temps.

Had that already before on other cars.But never had a frozen brake line...
 
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