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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Suspension | Brakes | Chassis > E90 320D Brake pedal sinks to bottom engine on or off



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      11-14-2018, 02:41 PM   #1
mikesunboxing
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E90 320D Brake pedal sinks to bottom engine on or off

Hi Everyone this is my first post here, I have been lurking around for a long time as a previous owner of a E36 Cabrio E36 Tourer E46 Tourer and E46 Cabrio :-)
I just replaced the pads all round on my new (to me) E90 320d and changed the wear sensors etc. But not new disks, although they are a little low, but should have a few 1000 left.

Anyway after changing the pads I noticed straight away that the pedal travel was mental! It goes straight to the floor a few time then firms up a little but still a lot more travel than i am used too.

The pedal works and the brakes seem okay. But waiting at lights with foot on the brake, the pedal very slowly falls to nearly the bottom. This happens with engine running or not. So i am pretty sure it isn't the brake booster or servo.

Is it likely i have damaged a seal whilst pushing the pistons back? The filler cap was off when i did it to release any pressure.

Any help of pointers would be gratefully received.
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      11-14-2018, 08:39 PM   #2
TheeGovernor
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Quote:
Originally Posted by mikesunboxing View Post
Hi Everyone this is my first post here, I have been lurking around for a long time as a previous owner of a E36 Cabrio E36 Tourer E46 Tourer and E46 Cabrio :-)
I just replaced the pads all round on my new (to me) E90 320d and changed the wear sensors etc. But not new disks, although they are a little low, but should have a few 1000 left.

Anyway after changing the pads I noticed straight away that the pedal travel was mental! It goes straight to the floor a few time then firms up a little but still a lot more travel than i am used too.

The pedal works and the brakes seem okay. But waiting at lights with foot on the brake, the pedal very slowly falls to nearly the bottom. This happens with engine running or not. So i am pretty sure it isn't the brake booster or servo.

Is it likely i have damaged a seal whilst pushing the pistons back? The filler cap was off when i did it to release any pressure.

Any help of pointers would be gratefully received.
May be see if you are loosing any fluid from the brake fluid reservoir? Sounds like a bad master cylinder- I wouldn't expect it to fail when replacing the brake pads.
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      11-15-2018, 01:18 PM   #3
bluewater328
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Quote:
Originally Posted by mikesunboxing
Hi Everyone this is my first post here, I have been lurking around for a long time as a previous owner of a E36 Cabrio E36 Tourer E46 Tourer and E46 Cabrio :-)
I just replaced the pads all round on my new (to me) E90 320d and changed the wear sensors etc. But not new disks, although they are a little low, but should have a few 1000 left.

Anyway after changing the pads I noticed straight away that the pedal travel was mental! It goes straight to the floor a few time then firms up a little but still a lot more travel than i am used too.

The pedal works and the brakes seem okay. But waiting at lights with foot on the brake, the pedal very slowly falls to nearly the bottom. This happens with engine running or not. So i am pretty sure it isn't the brake booster or servo.

Is it likely i have damaged a seal whilst pushing the pistons back? The filler cap was off when i did it to release any pressure.

Any help of pointers would be gratefully received.
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Originally Posted by TheeGovernor View Post
May be see if you are loosing any fluid from the brake fluid reservoir? Sounds like a bad master cylinder- I wouldn't expect it to fail when replacing the brake pads.
Master cylinder sounds possible.

Our brakes can get stuck pistons pretty easy (usually the inside pad suffers) - so could be it is a stuck piston as you say.

But check the basic/easy stuff first: when's the last time you changed your brake fluid and bled the system?

Last edited by bluewater328; 11-15-2018 at 01:27 PM..
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      11-16-2018, 10:37 AM   #4
FCobra94
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Bleed all 4 corners and also look at the condition of the check valve, vacuum hoses, etc. going to the booster.
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      11-19-2018, 06:25 PM   #5
mikesunboxing
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so i have taken the calipers off and replaced the pads all round and now the disc as well.
Bled the rears today and the fluid was pretty dark. Not like cola, but like a dark lager.
Lost the light so still need to do the fronts, but there also seemed to be quite a lot of air in the lines.

Fingers crossed a good bleeding will improve things.
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