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Suspension & Braking
Have some questions about suspension or brake setups for your E46 BMW? Get all your answers here!

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Old 05-03-2013, 12:58 PM   #1
paraklas
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Brake master cylinder issue video incl.

A few days ago I noticed a hisshing sound coming after some tracing from the brake cylinder. It sounds as air leaking from somewhere. The leak stops if I press the brake pedal even slightly. Doesnt matter if car is moving or not but it does increase a bit when decelerating. When I shut the engine the leak slowly stops. It definitely comes from the brake cylinder. What does this mean?? There is no change on brake performance although after prolonged engine braking I think it looses some brake boost on first pedal press.

Time for new cylnder???


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Old 05-03-2013, 01:22 PM   #2
///MPR77
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Re: Brake master cylinder issue video incl.

Have you inspected the brake fluid reservoir area, brake booster line?

Have you done any recent work in that area, or any recent work at all?

To my understanding, when the brake master cylinder fails, brake fluid will leak on the floorboard, and you will loose pedal pressure.

localize that sound, and likely you will find the problem.

Is the sound coming from under the hood?... I assume the camera is pointing at the pedal to show how input at the pedal, directly has an effect on the sound.

I haven't had an issue like this, so I am in for the info.


GL.
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Old 05-03-2013, 02:41 PM   #3
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probably the sucking jet pump that sits next to the intake manifold. trace the vacuum line coming out of the brake booster. check that check valve and sealing gasket as well. older E46s have a weaker SJP that is known to fail/crack.
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Old 05-03-2013, 02:54 PM   #4
paraklas
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Quote:
Originally Posted by ///MPR77 View Post
Have you inspected the brake fluid reservoir area, brake booster line?

Have you done any recent work in that area, or any recent work at all?

To my understanding, when the brake master cylinder fails, brake fluid will leak on the floorboard, and you will loose pedal pressure.

localize that sound, and likely you will find the problem.

Is the sound coming from under the hood?... I assume the camera is pointing at the pedal to show how input at the pedal, directly has an effect on the sound.

I haven't had an issue like this, so I am in for the info.

GL.
I haven't done any work to the car, it started all of a sudden. There is no brake fluid leak, neither I'm low on brake fluid. The sound comes from the actual brake booster area, this is a RHD vehicle, the brake booster is in left side of the engine bay, right behind the alarm hood switch. Yes correct about the camera pointing, also it helps isolate the engine noise away, I can't record it from the outside as the engine noise covers the leak.


Quote:
Originally Posted by Mango View Post
probably the sucking jet pump that sits next to the intake manifold. trace the vacuum line coming out of the brake booster. check that check valve and sealing gasket as well. older E46s have a weaker SJP that is known to fail/crack.
But the sound does come from the brake booster area, exactly on the other side of the intake area. I am 100% positive about this. The video I took, was from inside the car as the engine noise is isolated away this way.

When I shut the engine I can still hear the "leak" for a few more seconds until it fades away. It definitely has something to do with either the hose next to the booster area or the actual brake booster? i.e. the vacuum diaphragm inside
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Old 05-04-2013, 08:46 AM   #5
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After a long day testing, I confirmed the hoses from the intake mani up to brake cylinder are ok. Leak comes from inside the brake cylinder. It seems as if the brake booster diaphragm has failed, seeing as it doesn't have a separate part number, I have a feeling it will be an expensive job to fix
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Old 05-04-2013, 07:34 PM   #6
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Re: Brake master cylinder issue video incl.

Quote:
Originally Posted by paraklas View Post
After a long day testing, I confirmed the hoses from the intake mani up to brake cylinder are ok. Leak comes from inside the brake cylinder. It seems as if the brake booster diaphragm has failed, seeing as it doesn't have a separate part number, I have a feeling it will be an expensive job to fix
Interesting...I haven't heard of anything like this, please keep the thread updated.

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Old 05-05-2013, 03:07 AM   #7
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There has been just another documented diaphragm failure creating the hishhhh sound after thorough searching here. Upon complete failure, the brake assist stops, making the pedal very hard to press. I've seen a couple of videos on youtube describing diaphragm issues on T50 ATE brake servos (T52 on the E46).

The leak can be verified that comes from inside the servo by just placing your ear on it while engine running, easy to listen to the leak. Also if I take the lower steering cover out and "massage" the rubber boot that covers the brake shaft, I can hear the air leak flow changing. Anyway, this is DIY testing for sure. Have in mind this is on a RHD E46, meaning the brake servo is on the other side of the engine, away from the intake manifold which makes it tons easier to pinpoint the sound. A vacuum hose or connector leak vs diaphragm leak on LHD cars will be more difficult to check.

Pelican parts has the cheapest one so far at $174 including the brake cylinder o-ring and a nut, if you add a brake cylinder rebuild, etc that I will probably do since "i'm there", brake fluid and various clamps, hoses, gaskets, cost should be around $250. The most common cause of the diaphragm failing is brake fluid leak from the master cylinder which corrodes rubber. This is one of the reason I want to also rebuilt the brake cylinder

On a RHD with ASC this involves emptying and removing the brake reservoir, disconnecting 2 brake lines, removing brake master cylinder, and then disconnecting the brake servo from inside the cabin. I will make a DIY as soon as I gather all the parts.

Edit: After reading and consulting, it is not recommended to rebuilt a brake cylinder if it leaks but to replace it.
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Old 05-07-2013, 11:04 PM   #8
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The booster job probably won't be fun.

If the MC itself isn't leaking, you might be able to bend/move the MC and lines far enough out of the way to get the booster out without cracking any fluid lines. I would make sure there is no brake fluid in the booster, either, as that means a failing MC killed the booster (fairly unlikely).
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Old 05-23-2013, 07:31 AM   #9
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^Yes, after removing the servo I will tear it apart to check for brake fluid, before installing the new unit.

The following items are being assembled and processed:

Qty: 1
07-11-9-904-295-M58
Collar Nut, 8 mm (Locking) -
Brand: OEM
$1.00

Qty: 1
07-12-9-904-567-BOE
Spring Clip, Flat, each
$0.75

Qty: 1
07-12-9-906-196-BOE
SELF-LOCKING HEX NUT M8-8-ZNNI SI
$2.50

Qty: 2
11-15-1-726-339-M395
Hose Clamp, 21-3mm -
Brand: Oetker
$2.00

(not part of the braking system but way cheaper than Cyprus)
Qty: 1
32-30-6-761-571-BOE
Genuine BMW Part: Swivel Joint With Universal Joint
$83.50

Qty: 1
34-31-1-160-133-M4
Grommet, Brake Fluid Reservoir to Master Cylinder, 25mm x 8mm, BMW 3 Series, All, (1992-99) -
Brand: Ate
$3.25

Ordered from SB BMW
34-31-6-750-384-BOE
Genuine BMW Part: Lock Valve
$19.75

Qty: 1
34-33-6-765-316-M4
Gasket for Brake Booster Check Valve
Brand: Ate
$2.25

Qty: 1
34-33-6-779-682-M4
Brake Booster (Vacuum Type) -
Brand: Ate
$174.75

$174 from USA, $700 from dealership here
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Old 12-14-2013, 07:39 AM   #10
swordsman11868
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Brake master cylinder issue video incl.

^Paraklas

Did u ever install a new MC or booster?

Just curious what the source of the leak was.

Thanks
Dan


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Old 12-16-2013, 05:00 AM   #11
paraklas
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^Paraklas

Did u ever install a new MC or booster?

Just curious what the source of the leak was.

Thanks
Dan


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installed new brake booster:
http://forum.e46fanatics.com/showthr...+brake+booster
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