11 captured repliesDiscussion pagination complete · Source accounts, not a confirmed diagnosis
THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCHMushy Brake Pedal
Reported or suspected cause
assuming it isn't the brake fluid
Reported cause
No successful repair reported for this finding.
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Identified cause
0
Suspected cause
0
Reported fixes
Read evidence and context
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Reported cause
But it does no good to try to jump the gun and figure out what the problem is assuming it isn't the brake fluid.
Leading evidence: 'assuming it isn't the brake fluid' (1 discussions report identifying this cause; no attributable repair resolution). Across 1 matching discussions, the most frequently mentioned possible cause is 'assuming it isn't the brake fluid' (1 discussions; 1 report identifying it and 0 suggest it). The most frequently discussed action is 'Replace brake fluid' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Suspected cause
If your car is a year or more old it is likely the fluid is bad.
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Suggestion
I think Porsche recommends a change every 2 years, but I do it every year in my street car, cheap insurance in my book.
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Suggestion
I am replacing the pads and a complete system bleed.
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11 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
Rennlist: 1 discussions
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The brake pedal on my 996 cab is mushy...it used to be firm like it should be. What could be the problem? I have not fooled with the brakes or boiled the fluid. I thought about bleeding them but how could air have gotten in the lines. I am not sure if this happened suddenly, I noticed today becuase I drove a Boxster and noticed the difference immediately.
My first piece of advice would be to look for leaks. Mainly around the master cylinder area. I've heard of 2 or 3 master cylinder leaks on MY 99 cars (what year is your car?).
How many miles on the pads (are they almost gone)?
When did you last change the brake fluid?
Brake fluid adsorbs moisture and then under heavy braking it vaporizes and becomes air (in your brake lines).
Shouldn't be pads yet. Too new, too few miles (since you have not been tracking the car).
Sure has all the symtoms of a leak and or massive air in the lines. If you don't do your own work I would get a dealer to look at them right away.
I can do my own work, I just do not know what the problem could be. I have not seen any fluid drips on the floor and I cannot figure out how air could have gotten into the lines.
[quote]Originally posted by Silver1.8T:
<strong>I have not seen any fluid drips on the floor and I cannot figure out how air could have gotten into the lines.</strong><hr></blockquote>
The system really isn't completely sealed. Even if fluid isn't dripping out, the brake fluid is still able to absorb water from around the seals. In time, you will have water and air in your system. This is why it is necessarily to regularly bleed the brakes.
Replace the brake fluid with high-quality DOT 4 and see if that helps. Don't overfill if the pads are almost gone else you will have a problem when you come to replace them.
Also don't forget to do the clutch at the same time.
After you've done this if it doesn't help then time to look elsewhere.
S.
The leak could be internal. That is, the master cylinder could be letting fluid by the seals when you apply the brakes. Does the pedal just feel soft or does the pedal go to the floor if you hold down long enough. If it's the later, then it is likely the master cylinder (although I have seen a rare occurance of a single leaking wheel piston). If it is the first instance (soft but does not go to the floor) I would try bleeding the lines. Either way you need to take some action as this is not safe.
[quote]Originally posted by Silver1.8T:
<strong>How could that much moisture have leaked in at only 15k miles. What else could be the problem?......I can do my own work, I just do not know what the problem could be. I have not seen any fluid drips on the floor and I cannot figure out how air could have gotten into the lines. </strong><hr></blockquote>
A small amount of moisture is enough to cause your brakes to feel spongy!
You are making a mountain out of a mole hill. Just have the fluid bled. Brake fluid will absorb moisture and may boil and cause air bubbles. If your car is a year or more old it is likely the fluid is bad. I think Porsche recommends a change every 2 years, but I do it every year in my street car, cheap insurance in my book.
Greg
[quote]Originally posted by Silver1.8T:
<strong>How could that much moisture have leaked in at only 15k miles. What else could be the problem?</strong><hr></blockquote>
It is a process of elimination. First you bleed the brakes. If that doesn't fix things you take a look elsewhere. But it does no good to try to jump the gun and figure out what the problem is assuming it isn't the brake fluid.
Most likely fixes first and then go down the list from there.
S.
I can sympathise. After doing a 2 day DE event with stock pads and Porsche fluid, the pedal went to the floor coming down hill into a sharp left hander(turn 6 @ NHIS). After the brakes cooled down enought to drive home the brake pedal was really mushy and they squealed like a stuck pig. Aweful! I am replacing the pads and a complete system bleed. I forget how bad it is to drive until I test drive a new Carrera here at dealership. The pedal should feel FIRM with minimal effort. Good Luck.
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