MrMoose

So a vacuum pump or vacuum booster failure can't cause the pedal to go to the floor. If either of those fail you'll lose brake boost, but the pedal will be high and hard and you should still be able to stop the car, just with increased effort.

I could be missing something, but at this point I can't think of anything but the ABS module. And if air suddenly got into that (without the fluid being low or leaks or something) then I'd think you'd need to replace the module, but I'm not an expert on ABS.

Note that the bleed pressure per the manual is 2 bar (29 PSI) not the 10-12 you're using. I know the pressure bleeder has all sorts of dire warnings about going over 15 but that's unless the manufacturer says higher, and Porsche says 29 PSI.

dgjks6

I'll try bleeding with the correct pressure

Also, ABS pump must not fail that often. New they are $3800, used $300.

Petza914

I use 20 psi in my Motive

Wayne Smith

Definitely need more psi than Motul recommends, or a willingness to wait for hours. But at a lower pressure (reduced flow speed) bubbles might not get pushed through.

I picked up a Mighty Vac to vacuum extract the fluid on Pam's GLA45. It worked very nicely, pulling the fluid through to the caliper rather than pushing it. No need to keep depressurizing the system to keep filling the master cylinder. They supply an adaptor to go onto the brake fluid bottle so you can place it upside down into the master cylinder so the master won't go dry. Unfortunately RBF600 comes in a bottle with a larger cap so no luck there.

I intend to try the vacuum system on the 997 when I next flush its fluid. If it works half as well as it did on the 45 it will be much better than the Motul, but I can't verify that yet.

I know Pete fills the Motul tank to do many cars at once and avoid draining the master. I did that once. Thought I had cleaned things up enough when I was done. On the next flush a year later I ended up with brake fluid everywhere. Well, fortunately my paranoia had me put the tank in a large garbage bag before pumping it up. But I did end up with a very messy garbage bag.

Note: Air in the system will make the pedal soft. Getting soft after the fact points to a system release feeding back to the master which points to the ABS.

MrMoose

Woof, that is not cheap, so I guess it really makes sense to see if that's the problem first. Do you have a way to pull codes, see if there are any faults in the ABS system? That would probably throw a brake warning light but I guess it's worth a shot.

I believe bleeding the ABS module requires using software to trigger the pump while pressure bleeding, but I've never done that myself (it's not necessary for normal bleeding). Honestly no idea if air in the ABS pump would cause your problem, or how air would get in there in the first place, or what else might be causing this issue for you.

dgjks6

Thank again all. At work so making a plan of attack for tomorrow.

I had a bad bad caliper on my Ford excursion. Similar symptoms but still had some brakes. Shop could not figure it out. Finally started replacing parts and found the problem.

Hoping for air in lines and ABS bleed. I have a device that will do it. And pray. Not thinking it will help because the symptoms are very similar to what I had happen before instituted this adventure. Unless air is somehow getting in the system.

Only other weird thing is all for brakes the inside of the rotors were bad and the outsides looked perfect. And in the rear the pads on the inside were more worn than the outside pads.

dgjks6

So was at work all night and I'm pretty convinced it's a bad ABS pump. So I learned all about that last night and found a used one on eBay. Then I found the instructions. So what is the difference between 1.4 and 1.5?

MrMoose

1.5 looks like an edit with a new torque setting that should have replaced 1.4. Probably an error or oversight as they appear to say the same thing.

dgjks6

That's what I thought.

So bled the breaks and had air in the fronts. And there was no break in on the front rotors. So maybe a second bad master cylinder?

MrMoose

At this point I really dunno what to tell you. Maybe you didn't get all the air out the first time because the pressure was too low? Or, yeah, the new MC or the old ABS module could be bad, I guess.

You sure you got all the air out? Are the brakes working at all now?

dgjks6

Pedal feels better.

But can't test drive tonight. I also feel like I've used more fluid that I got back out when bleeding.

I'm gonna pull the master cylinder again tomorrow and look to see if there is fluid leaking out the back.

CAVU

Porsche recommends approximately 2.0 BAR / 29 psi for the bleeding pressure.

Before you swap out a suspect new part, just want to double check:
- Primary circuit bleeding in this order: right rear, left rear, front right, front left.
- At least 250 ml drained per corner.
- Bleed through all bleeders screws, 2 per corner.
- Used "Super DOT 4" (would not be a factor for the issue you face currently).

I have replaced a number of master cylinders and do not recall ever having a bad one out of the box. There is always a first.

If you decide to do another bleed and it is still not right, you might bleed the secondary circuit, e.g. the antiskid circuit. There is a different procedure. A note from the manual: "Then, use the PIWIS Tester to bleed the brakes as well (secondary circuit). Only necessary if the hydraulic unit was replaced and if brake pedal travel is excessive after bleeding in the normal way (primary circuit). The process is menu-driven. Always observe the specified sequence rear left, front left, front right, rear right." I think it was discussed a few years ago.

Good luck!

dgjks6

All 4 corners bled with super dot 4. Used 2L so far.

I pulled the master without disconnecting it. Some moisture on the piston but no obvious leak.

Got up to 23 PSI and had my assistant pump the pedal for an old style bleed.

Ordered a used ABS pump

I got a couple code readers that will do the ABS bleed.

For the ABS bleed do you have to have all 4 corners up at the same time?

dgjks6

Progress. Bled at correct pressure and had a kid pumping and have some brakes now. I'd say 80%. I think you guys were right. I

1.Failed master cylinder followed by improper bleeding.
2.I'm an idiot

I fixed the first now just need to bleed correctly
Second is not fixable

Wayne Smith

Glad the first is helping. The second ... we're all guilty!!!