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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Suspension | Brakes | Chassis > Weird "Mushy" Brakes - Why is this happening?



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      03-13-2013, 10:47 AM   #1
07GraphiteXI
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Weird "Mushy" Brakes - Why is this happening?

07 328xi with ~84k miles

Recently after the car has been sitting for awhile (full workday - ~8-10 hours) I notice when I start driving the brake pedal is really soft and it doesn't seem to brake right away. Once I pump the brakes a bit, the pedal becomes pressurized and the brakes work fine. On the highway I've noticed the pedal is "softer" (hard to describe) when braking from highway speeds.

Pads have plenty of meat on them. I changed the front pads at ~75k miles and didn't replace the rotors - they were barely in spec at the time. Would that cause this? I also haven't replaced the brake fluid yet - though was planning on doing this with differential and transmission fluid soon.

Is this a mechanical problem/leak? My car is covered under CPO so I want to make sure I have some idea of what's causing this before I send it in...
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      03-13-2013, 10:49 AM   #2
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Brake Fluid...
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      03-13-2013, 11:09 AM   #3
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^that... or you have air in your lines, maybe need to be bled.
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      03-13-2013, 02:41 PM   #4
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check the fluid level first....if its below the "low" mark and you dont see any fluid in the reservoir...then air may have gotten in....

but it sounds more like you have a vaccum leak that looses pressure over time....Check all the hoses, brake lines, ect.....Look for leaks too....


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      03-13-2013, 03:01 PM   #5
07GraphiteXI
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I'll check the fluid level. If it's not low, I'm assuming it's a leak? Then that would warrant sending in to the dealership. I usually do my own work, but as long as it's under warranty I'll let the dealer handle it.

Thanks all.
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      03-13-2013, 03:22 PM   #6
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I would do a complete brake fluid flush first, if that doesn't help, I would put money on it being the master cylinder.
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      03-13-2013, 03:56 PM   #7
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+1 on a bad brake master cylinder. Try pushing in the pedal till it stops and holding your foot there. If it slowly sinks to the floor, it's more evidence pointing to a bad master cylinder.
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      03-14-2013, 10:11 PM   #8
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PS...the air needs to be bled out of the system or it will continue to feel mushy...


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      04-23-2013, 09:21 AM   #9
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I write it here in order not to open a new thread.

yesterday I had all my brake pads replaced with new ones and I also flushed the brake fluid.
my 320i has 37k and instead installed oem textar pads I decided to pick from ebay ferodo premier pads for both axles cause I read that they perform slightly better and also produce less dust.

after that, I have a mushy-spongy feeling whenever I use the brake pedal.
what might have happened?
could this issue be from the fact that new pads haven't yet match perfectly with the worn rotors? should I wait for a lets say 300miles? I ll plan to do a bed-in method but not now, I want to wait a week's time first.
could be air in the lines?
could be a faulty position of pistons?

please advise
many thanks
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      04-23-2013, 09:35 AM   #10
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A spongy feeling is usually air in the lines. When you bled the brake fluid did you make sure the reservoir didn't run low?
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      04-23-2013, 09:44 AM   #11
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I have heard of related issues with needing new brake hoses.....but I think its more air in the lines...


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      04-23-2013, 10:53 AM   #12
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yes, reservoir was constantly filled till top with fluid

when I returned back to my flat, I opened the reservoir again and used some force repeatedly on the brake pedal at about one minute (dsc and dtc lights went on in the dashboard) . I closed the reservoir , had a short distance and I then could find it just slightly better but not at all as the initially firm feeling before the change.

I don't know what to say...
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      04-23-2013, 11:17 AM   #13
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Quote:
Originally Posted by Terryk View Post
yes, reservoir was constantly filled till top with fluid

when I returned back to my flat, I opened the reservoir again and used some force repeatedly on the brake pedal at about one minute (dsc and dtc lights went on in the dashboard) . I closed the reservoir , had a short distance and I then could find it just slightly better but not at all as the initially firm feeling before the change.

I don't know what to say...
Whoever flushed the brake fluid didn't bleed the system properly. You need to bleed the brakes.
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      04-23-2013, 11:38 AM   #14
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Air.....Flush Every 2 yrs
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      04-23-2013, 11:43 AM   #15
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Quote:
Originally Posted by Terryk View Post
I write it here in order not to open a new thread.

yesterday I had all my brake pads replaced with new ones and I also flushed the brake fluid.
my 320i has 37k and instead installed oem textar pads I decided to pick from ebay ferodo premier pads for both axles cause I read that they perform slightly better and also produce less dust.

after that, I have a mushy-spongy feeling whenever I use the brake pedal.
what might have happened?
could this issue be from the fact that new pads haven't yet match perfectly with the worn rotors? should I wait for a lets say 300miles? I ll plan to do a bed-in method but not now, I want to wait a week's time first.
could be air in the lines?
could be a faulty position of pistons?

please advise
many thanks
re-bleed and let the pads bed in. If you're still having mushiness it could be the aftermarket pads. Not sure if they're a reputed/premium brand.
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      04-25-2013, 06:16 AM   #16
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thank you all for your messages and support.
by the time I went back to the garage I already had done around 100miles so the feeling was much better. they said that if there was air in the lines the brake pedal wouldn't stop in a specific position as it does now.
right now, I only have to use more strength if I want to have an immediate full stop.
probably I ll have to wait till the new brake pads mate with the old rotors.
I ll go for a bed in procedure tonight or tomorrow night the latest.
many thanks
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      04-28-2013, 09:15 AM   #17
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Check this thread:
http://www.e90post.com/forums/showth...5#post10468315

This may not be as simple of a fix as "just bleeding the breaks."
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