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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Suspension | Brakes | Chassis > Brake issue when start the engine.



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      02-07-2007, 06:12 PM   #1
wuli
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Brake issue when start the engine.

Hi:
I have my 06 330i Auto.
In order to start the engine we need to hit the brake, right? But for some reason, every morning when I hit the brake, my brake seems to be stock in the position, and I can only hit a little bit, after I start the engine, the brake become normal again.
Is anyone has the same issue as mine? Is that the pad or rotor or brake issue? This happened when the time I leave office back to home.
Do I need to call dealership to have a check?
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      02-07-2007, 07:13 PM   #2
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mine is like that...if i haven't driven it in awhile....i don't have to push all the way down..i just push gently...push and start button...the brakes immediately loosen once the engine has started...
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      02-07-2007, 08:59 PM   #3
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Your brakes are stiff when the car is off because the brake sytem turns on with the car. its completely normal, this is how all cars work. If you turn off your car after a drive and press the brakes a few times they will get hard to press. its just how the sytem works.
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      02-07-2007, 09:30 PM   #4
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That happens because. Everytime we start the car after a certain period of time. Our cars have this feature well the break is applied slightly for the first few seconds of driving, to dry up the brakes, or wipe off the rust. It is mostly a safety feature, I have noticed this and I think its really cool.
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      02-08-2007, 01:37 AM   #5
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I have a different opinion. The brake system does indeed operate when you start the car, but it is not a feature that it is stiff when the car has not been operated for a while. Try this, turn off the engine and push the brake, it feels kinda normal, now release and push again... you notice the difference? Release and push again, it should be too stiff. It is more like compressing the brake fluid because the of valve not being released back to rest position. It is not there to clean the discs or de-rust them as I had that in my old Ford Orion (I don't know if it was ever on the US market) and it is a very old car and rather cheap one. I've heard of people claiming that if you press brake when the engine is off and leave the car, there are chances that the hydraulic pipes of the brake system will spread open under specific conditions.

I'm no car mechanic, so I may be wrong in any of the above... if you are a car mechanic feel free to correct me (in a nice way, not rude :P )
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      02-08-2007, 01:47 AM   #6
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Quote:
Originally Posted by aarnt View Post
I have a different opinion. The brake system does indeed operate when you start the car, but it is not a feature that it is stiff when the car has not been operated for a while. Try this, turn off the engine and push the brake, it feels kinda normal, now release and push again... you notice the difference? Release and push again, it should be too stiff. It is more like compressing the brake fluid because the of valve not being released back to rest position. It is not there to clean the discs or de-rust them as I had that in my old Ford Orion (I don't know if it was ever on the US market) and it is a very old car and rather cheap one. I've heard of people claiming that if you press brake when the engine is off and leave the car, there are chances that the hydraulic pipes of the brake system will spread open under specific conditions.

I'm no car mechanic, so I may be wrong in any of the above... if you are a car mechanic feel free to correct me (in a nice way, not rude :P )

Thats pretty much what i meant i just didnt want to type it all out.
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      02-09-2007, 01:32 AM   #7
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You're ALL WRONG.


Just playing. But seriously.

Here's what's going on, kids.

Your brakes are assisted by engine vacuum. There is vacuum "pulling" your brake pedal, so that when you push on it, it's easier to push. When you shut off the engine, vacuum is no longer being created. The brake booster has a built in one-way valve so that when you shut off your engine, a certain level of vacuum is kept in the booster. This gives you a couple of assisted pedal-pushes in the event that your engine stalls while driving.

If you step on the brake after you shut off the engine, you are releasing that stored vacuum. This is why the pedal gets harder and harder. You use up all the "assist".

As for the OP:

There is a bulletin about the issue you are experiencing. Your booster's one way valve is busted, or the booster is internally faulted. Take it to the dealer, and let them have it for a couple days (need to check it in the mornings, when the problem is) and they'll take care of you.

Matt
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      02-09-2007, 11:55 AM   #8
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sounds pretty normal to me.... when the car is off and yo hit the brakes the brakes stiffen, you just have to bare touch the brake to turn the car on anyway.

i wouldnt worry
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      02-09-2007, 12:39 PM   #9
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Quote:
Originally Posted by ///Matt View Post
As for the OP:

There is a bulletin about the issue you are experiencing. Your booster's one way valve is busted, or the booster is internally faulted. Take it to the dealer, and let them have it for a couple days (need to check it in the mornings, when the problem is) and they'll take care of you.

Matt
You mean what the OP said, its out of spec. I feel the same stiffness too in the morning but the pedal quickly loses tension almost immediately after start-up....isn't this normal?
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      02-17-2007, 08:04 PM   #10
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Smile Get the repair from dealership

Finally I drop my car to dealership and they take care of it.
The following is repair description.

C/Reports brake pedal is very stiff to press first thing in the morning. When trying to start -- OK during the day.
Check valve leaking back too much vacuum over time. Tech removed cowl and checked vacuum to the brake booster.
Found good vacuum but bled off after several minutes.
Compared this to another E90 and found holding vacuum better. Removed dsc unit in order replace booster hose with check value. reinstalled dsc unit and bled brake system. Checked operation.

They replace 2 parts. One is pressure hose and the other is gasket.

Everything coming back very smoth for my E90 now.
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      02-19-2007, 11:36 AM   #11
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Is this dangerous? Mine started doing this after a few thousand miles, but I thought it was because the weather had gotten colder. Do I NEED to take it in, or can it wait until Im in for servicing?
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      03-08-2007, 11:22 PM   #12
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Quote:
Originally Posted by Fraggy View Post
Is this dangerous? Mine started doing this after a few thousand miles, but I thought it was because the weather had gotten colder. Do I NEED to take it in, or can it wait until Im in for servicing?
same here. I also noticed that if I pump the brakes while on idle (car stopped and engine runnig), pedal gets stiffer and stiffer. I repeated this with the car
in motion = ~30-40 mph, neutral, engine at idle and had not stiffening.

It looks like the assist behaves differently at different speed.

When the car was new (now ~12k) I never had this.

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