Sinking brake pedal...

[Lolvoguy]

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

 

[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.

 

[ruhroh]

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.

 

[A_Harman]

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.

 

[Wolf359]

If the fluid level hasn't changed, as others said, probably the master cylinder.

 

[Lolvoguy]

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

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

 

[Linctex]

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.

 

[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.

 

[LeakySeals]

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

 

[Lolvoguy]

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.

 

[andyd]

Rear drum brake shoes need adjusting?

 

[Silverado12]

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.

 

[Lolvoguy]

yup, I sure do have rear drums.

thanks for the tip