Throwing in the towel... my brakes have defeated me

[chrisbruck]

My brakes have beaten me... taking it to the local Porsche race shop and have them sort it out next week. I'm tired of bleeding brakes and second guessing myself on everything I've done. I even bought this car because of the pure mechanical nature to it and "ease" and pleasure of working on it, which just adds to my frustration.

I basically refreshed the whole brake system over Xmas and have been chasing a squishy pedal ever since. Pretty much 99% sure my "new" ATE master cylinder from our host is defective. After my last bout of patient bleeding tonight, the pedal slowly but surely drops to the floor consistently now. No leaks, no fluid loss. Can only be the MC but since I replaced everything too, not 100% sure.

Tired of second guessing and, for them to sort it out for $600, probably worth it to be safe. I could order another new MC but I'm concerned the same thing may happen again. Maybe it's something I did during the install, maybe it's just bad. I'm just tired of worrying about it.

Thanks to all the advice and help on my previous posts. Been very helpful and I'm sure the shop will probably say, "yup, it's just a bad MC" to at least make me feel good I did all the right things.

For now, giving up on this one.... Porsche 1, me 0.

[allaircooled]

Is there a warranty on the mc?

[porsche930dude]

i chased the same problem with my car. drove it with a squishy pedal for 6 years. I changed the pads because they were getting low and of unknown age and solved the problem

[Ronnie's.930]

Originally Posted by porsche930dude

i chased the same problem with my car. drove it with a squishy pedal for 6 years. I changed the pads because they were getting low and of unknown age and solved the problem

But would your pedal sink to the floorboard like the OP's does?

[emac]

Chris. Just a car, think of any other car you have ever worked on. You are bleeding back into MC. My guess is its bad. There would be no leaks with what you describe
Ernie 81sc

[porschenut]

Next time, don't bench bleed the MC before installing it. Some guys do that but I didn't do it the two times I replaced them in my cars, and I ended up with a nice hard pedal. I don't believe bubbles are likely to get trapped in there as any air will escape up into the reservoir above it. My guess is you may have damaged the MC during the installation. Or, it could have been defective out of the box.

BTW, are you sure it's not leaking? If the MC does leak, the fluid will puddle at the base of the pedal cluster, not on the garage floor. Make sure you check behind the wooden board for signs of fluid in the pedal area.

[earossi]

Chris,

Don't give up just yet. Years ago, I pulled the calipers off a 911T to rebuild them on my work bench. Reinstalled the rebuilt calipers on the car and then bled the system. The result was a very squishy pedal. I then re-bled the system twice with no improvement in pedal feel.

Scratching my head, I then took a look at the calipers and determined that I had reversed the calipers. They are not identical, though I thought them to be so! When they are swapped incorrectly (right caliper mounted on left side, and vice versa), they will bolt up just fine; however, swapping them left to right ends up putting the bleeders on the bottom of the caliper......so it was impossible to bleed the air out of the system. I reversed my installation, and they bled down perfectly the first time!

Any chance you may have made a similar mistake?

[don911]

Did you install the o-ring on the MC? When I installed the 23mm MC for my 930 brakes I didn't realize there was an o-ring on the MC. I could pump and get pressure but it wouldn't hold pressure and the pedal would slowly go to the floor.

[racetek]

I had the same problem, rebuilt all the calipers, new hard lines, new soft lines and NEW master cylinder. Bled them to death, and still the pedal sank to the floor. The secret is to have someone listen to the brake fluid reservoir. The MC can leak back to the reservoir allowing the pedal to sink to the floor and you can hear the fluid returning. I put a kit in my old MC and all was OK.

[Texel]

I think Racetek is on to it, fluid leaking back past the piston in the master cylinder doesn't leak anywhere but causes the pressure to be lost. It can be as simple as the piston seal being ripped or torn on installation, or the bore being damaged. One of my landrovers did exactly that on the clutch master cyclinder. With the clutch pedal down in gear it would slowly crawl away as the fluid pushed past the piston. Easily fixed

The seal is probably worth next to nothing from a brake or clutch shop and well worth trying.

Cheers

[T77911S]

Originally Posted by porschenut

Next time, don't bench bleed the MC before installing it. Some guys do that but I didn't do it the two times I replaced them in my cars, and I ended up with a nice hard pedal. I don't believe bubbles are likely to get trapped in there as any air will escape up into the reservoir above it. My guess is you may have damaged the MC during the installation. Or, it could have been defective out of the box.

BTW, are you sure it's not leaking? If the MC does leak, the fluid will puddle at the base of the pedal cluster, not on the garage floor. Make sure you check behind the wooden board for signs of fluid in the pedal area.

when i saw that you did that in your other post i did not think that was a good idea.
i have always blead the MC on the car. actually never heard of doing it on the bench.
i just crack the lines at the MC to bleed it, then do it at the wheels. another thing, and i think you may have done this, is to wait a week or so then bleed them again.
what type of fluid are you using? DOT?

[chrisbruck]

I've checked and rechecked everything numerous times. Calipers are on the right way, put the O-ring on where is connects to the booster didn't overtighten it, used ATE Gold fluid up until last night when I used some local DOT 4 fluid just to bleed it a whole lot. Looked everywhere for leaks, never once needed to add fluid, level has been rock steady.

The only iffy things are 1). I didn't bench bleed it real well and 2). I'm sure I've pushed the pedal down farther than most say to to work out the bubbles. Hard to believe you can damage the seals on a NEW MC by overextending it but maybe you can.

Now like I said earlier, the pedal consistently goes to the floor with light pressure with the car on or off. Noticeably more when idling but then you have the vacuum booster helping. A quick stab of the pedal creates good stopping pressure but then it slowly drops with steady even pressure.

It's got to simply be the MC internal seals.

[awhnry]

In my experience, it is going to be something incredibly simple and basic. We will all hear you slap your head when you find out what is wrong. My vote is bad MC; is it a new or rebuilt?

[chrisbruck]

I agree it's got to be something simple.

It's a new MC from ATE I bought from our host in Dec. Checking to see if they will take it back now.... if so, I may give it one more shot by replacing the MC again myself.

[mreid]

Your master cylinder is bad. Your symptoms are classic.

[allaircooled]

Originally Posted by chrisbruck

I agree it's got to be something simple.

It's a new MC from ATE I bought from our host in Dec. Checking to see if they will take it back now.... if so, I may give it one more shot by replacing the MC again myself.

That's what I would do. Sounds like it is leaking internally. That is why I posted my previous post that seemed to have got ignored.

[roblav]

Agree... Looks like internally leaking master cylinder.

[dtw]

What method are you using to bleed the brakes - 2-man system, or a pressure bleeder on the reservoir? When working with a completely dry system, I seem to have the best luck with a pressure bleeder.

Bleeding a dry system on a 911 can be frustrating. So many times I have bled them, cursing the MC and the engineers for not including a bleed nipple on the MC itself (side note: you should have heard me whooping when I was bleeding a dry system on my 928 and discovered a perfectly-positioned bleed nipple on the MC...sooo happy).

Totally agree with the comments above - with a buddy working the pedal, put a stethoscope or ear on the reservoir while the pedal is dropping.

The best lesson I learned after bleeding dry systems on 911s...buy plenty of store-brand DOT-4 dreck in the biggest size they've got. Save the Super Blue until the pedal firms up, then bleed out the dreck.

[CCM911]

If you arepast the return period, can you just buy an MC rebuild kit?

Don't give up, you are almost there, and $600 will feela lot better in YOUR pocket.

Also, did you rebuild the calipers? Sometimes the pistons are forced back out due to the new rubber seals. I hope someone could explain this better than I.

[chrisbruck]

UPDATE...

Super helpful, friendly, wonderful Pelican Customer Service said this is still under warranty and are sending out a new MC today. Will give it another shot to fix myself.

Thanks for all the advice and will post my results next weekend when I get it installed!!