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Sinking brake pedal... #4525780
09/25/17 12:15 PM
09/25/17 12:15 PM
Joined: Feb 2014
Posts: 2,606
Canada
Lolvoguy Offline OP
Lolvoguy  Offline OP
Joined: Feb 2014
Posts: 2,606
Canada
Recently I noticed that the brake pedal on my Focus seems to sink to the point of almost contacting the floor mat. It seems to happen once every few months, and only occurs once.

In terms of maintenance, the only thing I've replaced are the front pads and rotors. Everything else is OEM from 2007 (car has 100k miles currently).

Any idea of what could be causing it? I recently checked the drivers side floor mat and didn't notice any leaks (from the master cylinder). I've never encountered this issue on any car I've owned before.

thanks in advance


06 Lexus IS350- Wife
88 BMW 325is- Mistress
Say "no" to Turbo!
Re: Sinking brake pedal... [Re: Lolvoguy] #4525790
09/25/17 12:24 PM
09/25/17 12:24 PM
Joined: Jun 2003
Posts: 10,537
Illinois
javacontour Offline
javacontour  Offline
Joined: Jun 2003
Posts: 10,537
Illinois
Master cylinder is probably on the way out...

Fluid doesn't leak out of the MC, but it does get past the seals inside the MC and the pedal sinks.


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Re: Sinking brake pedal... [Re: Lolvoguy] #4525791
09/25/17 12:25 PM
09/25/17 12:25 PM
Joined: Dec 2016
Posts: 122
NC
ruhroh Offline
ruhroh  Offline
Joined: Dec 2016
Posts: 122
NC
A good start would be to borrow a brake bleeder tool from Autozone or AAP and replace the brake fluid. If the fluid is that far gone, the master cylinder is probably going to follow soon.

Re: Sinking brake pedal... [Re: Lolvoguy] #4525824
09/25/17 01:04 PM
09/25/17 01:04 PM
Joined: Oct 2010
Posts: 7,101
Michigan
A_Harman Offline
A_Harman  Offline
Joined: Oct 2010
Posts: 7,101
Michigan
Sounds like a master cylinder to me. I had a Chevy Vega a long, long time ago that had a brake pedal that would occasionally sink to the floor. I didn't think much of the problem until the master cylinder failed completely when I was in heavy northern New Jersey traffic. Then had to drive home with NO BRAKES.

Have that problem looked after immediately.

Last edited by A_Harman; 09/25/17 01:05 PM.

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Re: Sinking brake pedal... [Re: Lolvoguy] #4525846
09/25/17 01:21 PM
09/25/17 01:21 PM
Joined: Apr 2012
Posts: 5,595
MA
Wolf359 Online content
Wolf359  Online Content
Joined: Apr 2012
Posts: 5,595
MA
If the fluid level hasn't changed, as others said, probably the master cylinder.

Re: Sinking brake pedal... [Re: Lolvoguy] #4525850
09/25/17 01:27 PM
09/25/17 01:27 PM
Joined: Feb 2014
Posts: 2,606
Canada
Lolvoguy Offline OP
Lolvoguy  Offline OP
Joined: Feb 2014
Posts: 2,606
Canada
Just checked the fluid level...seems the same as before (just below Max).

Spoke with a reputable shop I usually work with. They said that unless it's dropping the pedal consistently, they'd just be throwing parts at it randomly with the hopes of fixing the problem eek

So where do I go from here? I really don't mind getting someone else to replace it as it's kinda outta my expertise level. I really don't mind getting another master installed.

I live in an area with VERY steep mountains/hills and high speed braking that's part of my daily commute. My brakes are VERY important to me.

thanks in advance


06 Lexus IS350- Wife
88 BMW 325is- Mistress
Say "no" to Turbo!
Re: Sinking brake pedal... [Re: javacontour] #4525856
09/25/17 01:35 PM
09/25/17 01:35 PM
Joined: Dec 2016
Posts: 7,174
Waco, TX
Linctex Offline
Linctex  Offline
Joined: Dec 2016
Posts: 7,174
Waco, TX
Originally Posted By: javacontour
Master cylinder is probably on the way out... Fluid doesn't leak out of the MC, but it does get past the seals inside the MC and the pedal sinks.


This is generally the most common and typical issue.


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Re: Sinking brake pedal... [Re: Lolvoguy] #4525863
09/25/17 01:43 PM
09/25/17 01:43 PM
Joined: Jun 2003
Posts: 10,537
Illinois
javacontour Offline
javacontour  Offline
Joined: Jun 2003
Posts: 10,537
Illinois
It probably happens when the weather gets colder. Once the MC heats up, the seals expand and you don't experience the problem again.


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Re: Sinking brake pedal... [Re: Lolvoguy] #4525873
09/25/17 01:50 PM
09/25/17 01:50 PM
Joined: Feb 2011
Posts: 6,769
Hudson, NH
LeakySeals Offline
LeakySeals  Offline
Joined: Feb 2011
Posts: 6,769
Hudson, NH
You should try turkey basting the MC a few times, let it marinate then bleeding brakes. That helped reverse the sinking pedal problem once for me. Black crud was preventing MC from sealing. Got that cleaned out, was fine for another 75k and traded away


06 Escalade 6.0L LQ9 AWD 165k M1 0w40
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Re: Sinking brake pedal... [Re: javacontour] #4525923
09/25/17 02:39 PM
09/25/17 02:39 PM
Joined: Feb 2014
Posts: 2,606
Canada
Lolvoguy Offline OP
Lolvoguy  Offline OP
Joined: Feb 2014
Posts: 2,606
Canada
Originally Posted By: javacontour
It probably happens when the weather gets colder. Once the MC heats up, the seals expand and you don't experience the problem again.



Mine is the opposite. As the MC heats up from use, is when it starts to fail.

Cold and it's fine.


06 Lexus IS350- Wife
88 BMW 325is- Mistress
Say "no" to Turbo!
Re: Sinking brake pedal... [Re: Lolvoguy] #4525973
09/25/17 03:46 PM
09/25/17 03:46 PM
Joined: Sep 2004
Posts: 7,826
Marshfield , MA
andyd Offline
andyd  Offline
Joined: Sep 2004
Posts: 7,826
Marshfield , MA
Rear drum brake shoes need adjusting?


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Re: Sinking brake pedal... [Re: andyd] #4525998
09/25/17 04:13 PM
09/25/17 04:13 PM
Joined: Feb 2013
Posts: 3,341
Central Virginia
Silverado12 Offline
Silverado12  Offline
Joined: Feb 2013
Posts: 3,341
Central Virginia
Originally Posted By: andyd
Rear drum brake shoes need adjusting?

This. The biggest clue is it's happening once, and the second time you apply brakes it's working fine. Adjust the rear brakes and make sure your parking brake isn't adjusted too tight. Of course, this is considering you have rear drum brakes.


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Re: Sinking brake pedal... [Re: Lolvoguy] #4526635
09/26/17 10:14 AM
09/26/17 10:14 AM
Joined: Feb 2014
Posts: 2,606
Canada
Lolvoguy Offline OP
Lolvoguy  Offline OP
Joined: Feb 2014
Posts: 2,606
Canada
yup, I sure do have rear drums.

thanks for the tip thumbsup


06 Lexus IS350- Wife
88 BMW 325is- Mistress
Say "no" to Turbo!

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