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Go Back   Bimmerfest - BMW Forums > BMW Model Discussions > 5 Series > E39 (1997 - 2003)

E39 (1997 - 2003)
The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

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  #1  
Old 12-24-2015, 01:08 PM
hans747 hans747 is offline
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Stiff brakes and misfire in heavy rain

Today, I was taking the family to see the movie "Elf" at the local brew-n-view today and it was raining hard. We hit a few big puddles, and I noticed that the brake pedal became very stiff (intermittently). The car ran fine for the rest of the trip, and we enjoyed the movie.

When we came out, the brakes had normal pressure, but the car was misfiring. It idled a little rough, and then when I pulled into traffic it started to die, blew a lot of steam, and threw a CEL. I pulled over, and shut the car off for a couple minutes while I poked around under the hood.

When I restarted the car, it ran perfect. No CEL, no stumbling, no hard pedal. Drove fine all the way home.

Now, I've looked around and found that this might be caused by vacuum leaks pertaining to the brake booster. It makes sense that water in the booster would make it stiff, and water in the vacuum lines could make an engine rough. But I'm not sure where I should start looking.

Has anyone else experienced this? If so, please share the places where you found leaks.

Thanks!
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  #2  
Old 12-24-2015, 01:23 PM
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energizedmortal energizedmortal is offline
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My brake booster had water in it winter 2014. I had misfires, locked brakes, etc.
This is a serious safety issue that must be addressed.

In short, I drilled a 1/2 inch drain hole where the microscopic flood prone half moon drain is and replaced the brake booster (did not replace master cylinder).

Brakes work great again and the brake booster area has not flooded since. Good luck.
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Old 12-24-2015, 02:26 PM
hans747 hans747 is offline
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Thanks for the advice.

Where is the half-moon drain located? Is this part of the lower windshield cowl? part of the brake booster? or someplace else?
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Old 12-24-2015, 02:47 PM
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energizedmortal energizedmortal is offline
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Quote:
Originally Posted by hans747 View Post
Thanks for the advice.

Where is the half-moon drain located? Is this part of the lower windshield cowl? part of the brake booster? or someplace else?
Under the brake booster look closely you will see two half moon drains.
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Old 12-24-2015, 06:35 PM
hans747 hans747 is offline
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Ok thanks! I am putting the car in the garage this weekend to address a batch of problems. This one just kept to the top of the list.
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Old 01-19-2016, 08:50 PM
hans747 hans747 is offline
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Update: A month after this incident, I got into the car on a 10-degree morning. The brake pedal was frozen solid.

I immdediately thought it might be frozen water in the booster, and sure enough...

I let the engine idle for 30 minutes, but no improvement. Finally, I poured hot water over the booster and got it to loosen up.

I parked the car in the garage for about 9 hours, pulled the vacuum line, and inserted the sucking end of a small hand pump down into the booster. I drew out enough mucky brown water to almost fill a 20-ounce Coke bottle.

Then I used the same piece of plastic tubing (now attached to a shop vac) to draw out whatever little bits of water were left. A few small chunks of ice came up. As I am typing this, there is a hairdryer aimed at the bottom of the brake booster, and I will pull the rest of the water out.

It's crazy to think that I had this much water in the brake booster this whole time. Probably ordering a new one on payday!

Last edited by hans747; 01-19-2016 at 09:48 PM.
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Old 01-19-2016, 09:06 PM
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16valex 16valex is offline
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Nice job Hans7474! And thanks for the feed back. That's unbelievable. Damn BMW engineers.
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Old 01-21-2016, 12:52 AM
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emann117 emann117 is offline
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Quote:
Originally Posted by energizedmortal View Post
My brake booster had water in it winter 2014. I had misfires, locked brakes, etc.

This is a serious safety issue that must be addressed.



In short, I drilled a 1/2 inch drain hole where the microscopic flood prone half moon drain is and replaced the brake booster (did not replace master cylinder).



Brakes work great again and the brake booster area has not flooded since. Good luck.

Do you have a DIY on replacing the booster? How long did it take you?
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Old 01-21-2016, 05:25 AM
hans747 hans747 is offline
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Old 07-16-2016, 08:17 AM
petereconomos petereconomos is offline
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Peter Economos

To Hans 747,
Thanks for the great video and information regarding Brake booster replacement on a 540i.
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