mushy brake pedal

[jgurnari]

my brake pedal is mushy until I pump it then it’s firm, come to a stop and mushy again. i dont see any leakage in my parking spot and the reservoir is full. Master Cylinder?
i replaced MC a few years ago, about 10 miles ago.. how can diagnose properly?
would hate to buy fluid, bleed and find out it’s the master cylinder and waste the new fluid.

[andy s]

Well, start by bleeding the brakes, check your pads to see, a, are the really worn and b, are they worn on an angle as to stop the pads from touching the rotors flat

[jgurnari]

They are not worn enough to be changed and the are straight, not on an angle

[andy s]

Bleed Bleed Bleed until you know its not that, then maybe bad MC or could be bad seals in the calipers? Or did you change fluid to DOT 5?

[jgurnari]

Haven't changed or bleed fluid yet...was going to change it a month ago, just to change it...there were no issues at that time. Came back from vacation after a month, drove the car, that's when I first felt brakes mushy. Was not like that when I left. There is no leakage on the ground in my parking space.

[PeteKz]

Does the pedal slowly go to the floor when you are at a stop while holding your foot pressure on the brake? If it does, then you have a leak inside the master cylinder, probably due to corrosion or bad seals. If it stays in the same place, then you still have air bubbles somewhere in the system.

Since you replaced the MC 10 miles ago, I will bet money that you still have air bubbles hiding somewhere. It can be a real PITA to get them all out. See other threads here about how to do it. And because you did this "a few years ago", it's time to flush the old brake fluid anyway.

[HarryD]

Originally Posted by jgurnari

my brake pedal is mushy until I pump it then it’s firm, come to a stop and mushy again. i dont see any leakage in my parking spot and the reservoir is full. Master Cylinder?
i replaced MC a few years ago, about 10 miles ago..

If it has been 10 years since the fluid has been changed, it needs to be done (should be done annually). A liter of quality fluid is $10-15 dollars. If you do it yourself, it is less than hour of your time.

how can diagnose properly?
would hate to buy fluid, bleed and find out it’s the master cylinder and waste the new fluid.

First flush/bleed. look for leaks. Test. See Petekz comments.

[jgurnari]

thanks PeteKz. No, HarryD, the Master Cylider was changed 10 years ago, fluid 10K miles ago

[HarryD]

Originally Posted by jgurnari

thanks PeteKz. No, HarryD, the Master Cylider was changed 10 years ago, fluid 10K miles ago

Thanks for the clarification.

Was the pedal firm when it was changed. When did the soft pedal start?

FWIW, my MC failed this year. It was an internal failure with a pedal that initially was firm and then slowly fell to the floor. Pumping only provided temporary help. I have no idea how old it was but was in my car when I bought it 22 years ago.

I flush the fluid annually. How long ago is 10k miles for you? For me it is about 2 years.

[PeteKz]

You were missing the "K" in the "10 miles ago" in your first post.

Okay, so it did not do this before you went on vacation, but it is now. Therefore, probably not air in the system.

If you step on the brake pedal (once) and hold it down, does it slowly go to the floor? If you then pump it up, does it slowly go to the floor?

And let's make are we are speaking the same language: When you say "mushy" do you mean that it squishes or is springy instead of firm, or do you mean that the pedal goes closer to the floor before it becomes firm?

[jgurnari]

tomorrow morning, EST, i’m going to check to see if after u pump the brakes, if the crack holds firm or sinks to the floor. in the event I need a MC, i checked prices. i see a Porsche part is $658, ther is also MC’ s for $80 (URO part) and another ATE ($348). any thoughts?

[HarryD]

Originally Posted by jgurnari

tomorrow morning, EST, i’m going to check to see if after u pump the brakes, if the crack holds firm or sinks to the floor. in the event I need a MC, i checked prices. i see a Porsche part is $658, ther is also MC’ s for $80 (URO part) and another ATE ($348). any thoughts?

Good plan.

When I replaced my MC, I ordered the ATE Branded Part. ATE is the OEM Supplier to Porsche.

[safe]

Originally Posted by jgurnari

fluid 10K miles ago

Miles doesn't really affect brake fluid, age does, heat does and exposure does.

A youtuber did a test, an opened but sealed can of brake fluid was still good after a year, but fluid in an open mug was bad after 72 hours.

Change fluid often, its a cheap way of keeping MC and calipers fresh.

I think you have air in your system or the MC is bad again. Pump and hold the brakes, does the pedal sink to the floor? Do this several times and look for leaks. It's cheaper to bleed the brakes do that first.

[EC900]

Don’t discount the rubber brake hoses. They could be swollen internally.
Check the expiration date printed on them. Replace as a good measure if 20 yrs or more old.
Then re-bleed the system.

[jgurnari]

I found that the brake does NOT go down after I pump to where it gets firm. Which tells me, as all of you did, that it is not be my MC..per se. BUT my mechanic said that there are 2 "parts" or "sections" to the MC, one for front brakes and one for back. He said, considering the brake feels mushy when driving, but does not fall to the floor after I pump it firm, is that one of the 2 sections may be failing. That make sense?

[PeteKz]

You have to do two separate tests.
1. When you first step on the pedal (one time, not pumped up), does it go to the floor eventually? If so, you need a new or rebuilt MC because fluid is leaking past the internal seal from one chamber to the other (and then back to the reservoir). If it does not slowly go to the floor, then your MC is okay.

If it passes test 1, then:

2. If you have to pump up the brakes to hold the pedal at a normal height, then you are compressing air or something else in the system. Do not replace your master cylinder, but find out what is compressing. Most likely, that's air bubbles somewhere.

If the brake lines are original rubber 40 years old, I recommend you replace them, then bleed the system. Assiduously.

[jgurnari]

ok, i’ll do both