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Tell tale signs of a bad master cylinder

Yesterday I finished refreshing my brakes. Here is a list of what I did.
-New SS dot brake lines
-New zimmerman rear rotors
-Resurfaced front rotors
-PBR ultimate ceramic pads all around
-Motive pressure bleeder
-flushed system with ATE blue

Any way, my brakes have been progressively been getting worse over the past 5 or 6 months. The pedal has very little pressure. I can put the pedal to the floor with ease. After I refreshed the brakes and bled the system, nothing changed. The pedal really...sucks! I remember when it used to be rock hard! Now I very little confidence in my braking.

So when I drove the car to break in the new pads, I took it up to 40mph and put the pedal to the floor and it took several seconds to fully stop the car. Rather unnerving.

Is it time for a new master cylinder? I can't think of any thing else.
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Old 03-22-2008, 02:38 PM
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If your pedal is traveling to the floor then the m/c is not sealing the fluid to put pressure on the pads at the rotor surface. If the pedal travels only so far and you are not able to lock up or stop the car with authority, it could also be your brake calipers in need of rebuild.....or both the m/c needs replacement and calipers need rebuilding. If you have gone this far and you want to be confident in the entire braking system, you need to do the rest of the job IMO.
Good luck.
ps, what year car? Is it a boosted system as it could also be a booster in need of replacement.
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Old 03-22-2008, 04:07 PM
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Well I am assuming the booster works because the pedal gets softer when the engine is on. Anyway I'm not sure about the calipers needing rebuilding because they don't leak any fluid. Well for slippery slope's sake, let's say I need a new MC. Should I replace it with the standard replacement or upgrade to a 23mm turbo MC. Or is this too much for carrera brakes?
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Old 03-22-2008, 04:49 PM
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stock calipers, use a stock MC. You only need the larger MC if you have larger calipers and you need to move more fluid.
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Old 03-22-2008, 05:02 PM
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Quote:
Originally Posted by BeauBlues View Post
Anyway I'm not sure about the calipers needing rebuilding because they don't leak any fluid.
If they are partially siezed or sticky they won't leak fluid but won't clamp very well either. That was what I was thinking about when I read your post saying the pedal down as far as you could push it and the car is still rolling forward.
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Old 03-22-2008, 05:39 PM
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Tony, not to dismiss your idea, but I'm kind of doubting its the calipers. Reason, when I had to push back the pistons to put the pads in, they moved pretty easily. They didn't feel sticky or stuck in anyway. Is that a good sign?

I guess the answer that I want to hear is that it could ONLY be the MC or calipers that could cause these symptoms. Hoping that I can dismiss the calipers are bad. I am pretty set on getting a new MC now.
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Old 03-22-2008, 06:01 PM
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If the calipers are moving back in OK then that's good. You mention the pedal gets softer when you turn the car on. The one m/c test is to pump the pedal and keep pressure on it, start the car. The pedal should drop a bit but then stop. If it continues to slowly drop as you maintain pressure on the pedal, then you are likely confirming m/c replacement.
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Old 03-22-2008, 06:14 PM
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in this case it sounds like a bad MC only because you say you can't get good pedal pressure and it goes clear to the floor.

Check out this month's issue of Excellence excellencemag.com. They cover master cylinder replacement.

I have the pbr ceramic pads, and they are pretty good. I don't usually have the rotors resurfaced on a Porsche, simply because the brakes need all that meat on the rotors so that they can absorb the heat and act as an effective heat sink. when you remove material, it lessens the ability of the rotors to absorb heat energy, and you get more brake fade. Besides, for the cost of the refinishing, you can get new Zimmermann rotors anyway.

If you can get pedal pressure by pumping the pedal, and the pedal won't eventually press clear to the floor, then you have something else going on like retracted pistons or air in the system.
Old 03-22-2008, 06:44 PM
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Porsche Crest Rock Hard???

BeauBlues, "I remember when it used to be rock hard!" Heck, I remember those times as well.
Seriously, it does sound like that you need a new master cylinder. There were days in the past that I would have said to just rebuild it your self and put a kit in it. But it appears that now, it is easier just to swap out. It really does appear to be the MC, chances are there is fluid collecting in the booster, or at the pedal rod area at the floor board. Good luck!! Tony.
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Old 03-22-2008, 10:11 PM
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Thanks for all your input guys, I ordered a new MC. I'll give an update when done.
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Old 03-23-2008, 08:45 AM
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Sounds like the MC is bad.
Check to see if you have fluid in the trunk from leaking seals.
I cannot hurt to replace the MC in such an old car.....added security. Plus, make sure to use the Motive Bleeder to bleed the system, the old way of pumping the pedal to bleed puts wear on the internal seals and can lead to premature failure of the MC.
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Old 03-23-2008, 09:07 AM
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Ok, Hold the phone!!! Update. As of last night, my brakes have gotten better. I have not changed the master cylinder yet. Actually gotten better is an understatement, they are great again! The pedal "feel" however is only slightly firmer. I can still put the pedal to the floor but not as easily as I could before.

Ok, so my hypothesis is that when I refreshed the brakes there was air previously in the system, the pads where wearing thin, the ancient brake lines where probably deteriorating on the inside and the rotors had seen better days. So my brakes would naturally suck due to these conditions. Now, fast forward to today, I have new SS lines, pads and rotors. I know pads have a break in period where they don't really stop so well for the first 40 miles or so. I have also heard that the SS lines have a sort of break in period as well, but they take about 100 miles to settle in.

When I took the car for a drive immediately after I finished the brakes, the braking was horrible and the pedal pressure was awful. I first thought this was the MC, but now I am thinking that the SS lines were expanding and contracting trying to settle in. Now, I can just about lock up the wheels with the brakes the way they are.

So here is where I am left at now, really good braking but a semi soft pedal. Should I bleed the system a few more times and go from there, or should I just quit worrying and go back to sleep?
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Old 03-23-2008, 08:40 PM
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Please explain EXACTLY what you mean by the pedal still goes to the floor. You do not want the pedal traveling that far in any normal circumstance.
Secondly, you will want to bed in the brake pads. There should be an instruction in your box the pads came in, if not do a search on bedding brake pads. It is a successive series of hard stops from mid and higher speeds to bleed offf the gases from the resins in the pad compound. It will also mate your pads and rotors for better stopping.
Having said that, you still have a pedal issue unless your defintion of floor means something other than what I think.
Pump the pedal so the pads are fully in contact with the rotor and hold that pedal down, if it creeps slowly downward, you are back to m/c. Do this while stopped, car can be off.
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Old 03-24-2008, 04:03 AM
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I'm sorry, let me explain this a little better. Way back, when my brakes were good, I could barely press the pedal down, maybe a couple inches of travel. NOW, the pedal travel has increased by several more inches and is not as firm as it used to be way back when. The increase in travel ALLOWS me to put to pedal to the stop or floor or just as far as it can go BUT I don't need to shove it down that far to stop the car.

The brakes are great! All I am worried about, is this extra pedal travel. I am going to bleed the brakes a couple more times and see if I get ANY more pressure and things tighten up. Tony, I know you were having a hard time understanding what I was saying, but frankly this is all very hard to put in words.
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Old 03-24-2008, 09:13 AM
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I concur that if you can press the pedal all the down in any circumstance you still need to investigate the MC as a possible cause.
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Old 03-24-2008, 10:52 AM
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I guess I've got to agree with you guys. Yeah the brakes work, but somethings not kosher here. I think Ill go ahead and replace the MC.
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Old 03-24-2008, 11:03 AM
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It really sounds like you've got air in the system still. After replacing lines you can really run a lot of fluid through before clearing out all the air. How much bleed work did you do?

Also, if they were fine before you worked on them, why would the MC be bad all of a sudden?
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Old 03-24-2008, 11:07 AM
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if you pump up the brakes, get the pedal nice and stiff...then "relax" your foot pressure. dont let up, just relax it a bit. IF the pedal creeps to the floor, then the MC is bad. sounds like you just have more bleeding to do.
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Old 03-24-2008, 11:34 AM
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brake pedal goes all the way to floor ?
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Old 03-24-2008, 11:59 AM
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Remember, if the pedal travel has been minimal in the past, as he has stated, and now it has a lot of travel, he has likely put the O ring seals inside the m/c into the 'rough' ends of the inside bore and done damage to the seal. The only way around that is with a new m/c.
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