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Suspension & Braking Forum by BimmerWorld
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Old 12-12-2015, 08:59 PM   #1
beattie_03
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Join Date: Nov 2012
Location: Brisbane, Australia
Posts: 41
My Ride: 2002 318i
2001 318i - Failing Break Booster - Quick Question

Hey,

My brakes have started becoming extremely hard to press at low speeds (stopping at lights etc). It is intermittent. At high speeds it seems to be ok, but still every now and then it goes quite hard and not very effective.

When it does this, I hear the release of air at the brake pedal. Have done a fair bit of research and copied these tests from another post:

Brake Booster Inspection

Functional Test :

1.With the engine stopped, depress the brake pedal several times to deplete the vacuum reservoir, then depress the pedal hard and hold it for 15 seconds. lf the pedal sinks, either the master cylinder is bypassing internally, or the brake system (master cylinder, lines, modulator, proportioning control valve, or caliper) is leaking

The pedal did not sink.

2. Start the engine with the pedal depressed. If the pedal sinks slightly, the vacuum booster is operating normally. If the pedal height does not vary, the booster or check valve is faulty.

The pedal did not sink.

3, With the engine running, depress the brake pedal lightly. Apply just enough pressure to hold back automatic transmission creep. lf the brake pedal sinks more than 25 mm (1.0 in.) in three minutes, the master cylinder is faulty. A slight change in pedal height when the A/C compressor cycles on and off is normal. (The A/C compressor load changes the vacuum available to the booster.)
Pedal did not sink.

Leak Test:

1. Depress the brake pedal with the engine running, then stop the engine. If the pedal height does not vary while depressed for 30 seconds, the vacuum booster is OK. If the pedal rises, the booster is faulty.
The pedal height did not vary (maybe rose the smallest amount).

2, With the engine stopped, depress the brake pedal several times using normal pressure. When the pedal is first depressed, it should be low. On consecutive applications, the pedal height should gradually rise. If the pedal position does not vary, check the booster check valve.
The pedal position does not vary

Booster Check Valve Test

1. Disconnect the brake booster vacuum hose at the booster.
2. Start the engine and let it idle. There should be vacuum. If no vacuum is available, the check valve is not working properly. Replace the brake booster vacuum hose and check valve, and retest.
There is vacuum

So basically it was the same problems this other guy seemed to have, but his solution was never posted.

I took my under dash trim off to have a look at the connection there. There was a little bit of oil on the "ribbed hose" that goes through the firewall from the brake booster. Where is this from?

I cleaned that up and sprayed some detergent on there to check where the air leak was. The small ring gasket that covers the horizontal push rod connection to this 'ribbed hose' is leaking at the top.

First thought was to try and stop this leak but other posts have confused me. Alot of posts seems to document to fix this 'hissing noise', you replace the non return valve. The non return valve is before the brake booster (from vacuum pump) so that didnt quite make sense. But if vacuum is getting where it shouldent be (ie inside this ribbed hose on the inside of the car, then perhaps that does make sense.

My model seems to have the built in non return valve that is press fit onto the vacuum hose, which the dealer quoted me $120 for.

Firstly, is that likely to fix my problem?

Secondly, surely I can find a ribbed press fit return valve to replace that component only?

Thirdly, the leak from the horizontal push rod to the ribbed hose on the brake booster - should that be fully sealed (silicon etc) or is it only a problem because of a faulty non return valve?

Thanks in advance for any help!

PS: Attached photo shows the oil residue on this ribbed hose (back of brake booster) and also the circular ring gasket I am talking about which isnt fully sealed to the hose...
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Old 12-14-2015, 09:08 AM   #2
beattie_03
Registered User
 
Join Date: Nov 2012
Location: Brisbane, Australia
Posts: 41
My Ride: 2002 318i
So I have pulled out the old booster and ordered a new one - it was definitely coming from there.

Im assuming that none of this oil is supposed to be in there... it looks like oil not brake fluid though so where it is it from?

Is that a massive build up through the vac pump and vac hose?

If there is no oil etc transferred between master cylinder and brake booster, why the O-Ring at the connection.

Finally, whats doing on with the master cylinder there, obviously the seal is old and shot to **** but is that another source of oil where it shouldn't be?

PS: For anyone with a RHD 4 cylinder E46 with the ASC control right next to the brake booster - it is possible to get the entire brake booster out without disconnecting the any of the brake lines or brake reservoir - fiddly, painful, but means you shouldnt need to bleed the brake system etc.
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Old 12-16-2015, 09:19 AM   #3
paraklas
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Join Date: Jan 2006
Location: Cyprus
Posts: 6,332
My Ride: ESS TS2 320ci
Quote:
Originally Posted by beattie_03 View Post
So I have pulled out the old booster and ordered a new one - it was definitely coming from there.

Im assuming that none of this oil is supposed to be in there... it looks like oil not brake fluid though so where it is it from?

Is that a massive build up through the vac pump and vac hose?

If there is no oil etc transferred between master cylinder and brake booster, why the O-Ring at the connection.

Finally, whats doing on with the master cylinder there, obviously the seal is old and shot to **** but is that another source of oil where it shouldn't be?

PS: For anyone with a RHD 4 cylinder E46 with the ASC control right next to the brake booster - it is possible to get the entire brake booster out without disconnecting the any of the brake lines or brake reservoir - fiddly, painful, but means you shouldnt need to bleed the brake system etc.
no oil/fluid should be present in the brake servo. Here's my DIY, it's RHD although the ASC unit is on the opposite side
http://forum.e46fanatics.com/showthr...ht=brake+servo
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Last edited by paraklas; 12-16-2015 at 09:20 AM.
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