ClemCLone

In late April I bled my brakes, the 4 wheels. I hadn't done this since I had purchased the car in 2021.
New pads and rotors 2 years ago. I average 5K miles a year. 120K miles now.
I had not been having any problems.
The pedal feel was firm and braking was not an issue.

This spring, I was a bit alarmed at the color of the fluid, a definite green tinge.
After posting about this when I first changed it out, I got some comments that it was from copper tubing, a mix of old blue, etc.
(Is there any copper tubing in this brake system? I didn’t think so.)


Brake Fluid April

I use a Power Bleeder. I had used one with some Audi’s so I knew the drill.
Bleeding done, cleaned up. I took it for a drive.
The pedal was firm, almost too firm.
I’ll try to explain.
When stopping, then coming to a full stop, the pedal is firm, but it doesn’t feel like I have enough pressure on the pedal to stop,
It doesn’t ‘grab’ the rotors like it used to, to give you that sense you are really stopped.
It sort glides to a firm stop.
Does that make sense?

In mid-May, I bled the clutch system, got more full green-tinged fluid out.

Fluid from Clutch bleed

I bled the wheels also again, they were all clear.
Clutch feels the same, no problems, brakes are firm, but still, not feeling that are completely right.

Last night, driving in town, I was on a city street, 35 MPH. A car pulled out of an alley, hidden by cars on the side.
I was maybe 2 car-lengths or less away. I hit the brakes hard to stop, but it didn’t make me feel good and secure about making a full hard stop. Again, brake pedal is firm, but it never feels like it “locks to the rotors” properly.

I bled the system again today, all 4 wheels.
Fluid ran clear out of each caliper.
This is what I got.


Brake Bleed June 22
cloudy and green

I have not bled the ABS system. I have an iCarSoft that I believe can pump the ABS.

Pedal is firm, but it just doesn’t feel right.
Anyone here that can help explain this better?
Do you get what I say when the stopping doesn’t “feel” right?

TMc993

I know exactly what you're describing. It sounds as if your brake booster (Porsche PN - 997 355 923 00 in PET) may be bad or you may have a vacuum leak that is preventing the booster from functioning. That "hard-pedal-slow-stop" condition is really dangerous. I wouldn't drive the car until you get the problem remedied.

ClemCLone

That's what I'm afraid of.
Thanks. I'll look into it.
Why do you think it showed up with the system bleed?

TMc993

Difficult to say, but things like that do happen. The booster is mounted directly behind the master cylinder, but the link between the two is mechanical so it may just be an incidental thing or, it may not be the booster at all. Do make sure you didn't inadvertently knock a vacuum line loose or something like that when you were connecting the bleeder to the master. Also, don't assume that it is actually the booster without a definitive diagnosis to that effect. My "diagnosis" was a suggestion based on symptoms I've seen in the past that point to the booster but that may not be it at all.

ClemCLone

I remember a few times late last season after a 30 min drive and coming to a stop, the pedal being that same harness. That was intermittent and only felt that a few times.
I will check for a leak, the hose, the booster. No codes, no other vac. leak symptoms/problems. I've read also that my symptoms are as you describe. I'll need to look into this right away.

harveyf

I agree on the booster being a potential problem. The vacuum source is back at the engine, taken off the dual oil scavage/vacuum pump on the end of the bank 2 exhaust cam shaft. There are plastic lines that attach there. It also feeds systems that need vacuum on the top of the engine. Lots of places to develop a crack and a leak. I would consider getting a vacuum gauge hooked in somewhere and see if you are getting the full vacuum per spec, (although I don't have any idea what the spec value is!).

ClemCLone

Thank you for this. This was my next stop in diagnosing this. I saw on a YT vid the pressure should be around 18 lbs.
I'll look at this area today.
I'm not getting any codes on this or any other sign of a vacuum leak. If it is leaking, wouldn't that throw a code?

harveyf

On my 944's, I have in the past disconnected the vacuum line from the brake booster, just to see what it would feel like. It does feel exactly like you describe. You just can't physically push the pedal down hard enough to get a good stopping action.

I don't know what codes it might throw, frankly. I do know that the vacuum system for the brakes, besides its primary job of charging the brake power booster, has one branch, next to the connection to the pump. This branch feeds the system that actuates the two flapper valves inside the intake manifolds. It does not interface directly with the intake manifold system, in the sense of what we normally think of as vacuum leaks that cause the car to run badly. Since the Check Engine light only comes on with respect to emission related issues, it wouldn't necessarily throw a Check Engine light. That said, you would think Porsche might want to turn on a dash warning light if something was compromising your braking system! BTW, in general the small line that branches off to the flapper valves is attached to a plastic nipple right at the pump. It would be a good place to put in the tee that would feed a vacuum gauge. And if the nipple is broken, there's your problem! Regardless of the actual number, it should hold vacuum for a short while after you stop the engine. If you shut off the engine and the needle on your gauge immediately starts to taper off, that is probably a sign that you have a leak.

In the attached article on my website, the flapper valves are discussed. In the first video embedded in the article, around 8:37, is a view of the vacuum pump.

https://newhillgarage.com/2023/12/01...nd-components/

MrMoose

There are a few easy tests for the booster you can start with. The basics are (after driving) to turn off the car, then push the pedal a few times. The pedal feel should change over 2-3 presses as you bleed off the residual vacuum with each press. Now press the pedal down and start the car: you should feel the pedal sink a bit as soon as you start from the booster receiving vacuum.

I'm kind of worried about that blue, though. Is it possible the previous owner used DOT 5 silicone brake fluid? I believe that's blue/purple to differentiate it, and that would explain both the cloudiness and the color. The only other blue brake fluid I know of is ATE Super Blue, but that hasn't been sold in the US since around 2013 (it violated US requirements for glycol brake fluid to be clear or amber) so I doubt that's it, and that wouldn't cause cloudiness if mixed with the Prestone you're using.

If that color is, in fact, from silicone you're probably at minimum going to want to flush the entire system with denatured alcohol (including the ABS pump), dry it, and refill with glycol. If that's what happened it's definitely a very bad thing but I'm no expert on the issue or how best to recover the system, and I'm not sure if it could be contributing to your stopping problems.

ClemCLone

I believe I have found the problem.
Looking at the car where the scavenge oil/vacuum pump is, I found this small broken vac line off the top of the vac. pump fitting.

Broken Vac. line


Broken fitting


I can easily remove the vac line connector.
ECS Tuning has it in stock, 2-day shipping, total: $158

987-355-575-0

harveyf

Super deal! As a bonus, your car will accelerate better with the throttle body flap system functional.

ClemCLone

Yeah, hope this fixes it.
thanks.

TMc993

Nice detective work!

ClemCLone

thank you.
The best guide-help was to check the oil scavenger/vacuum pump.
And it's relatively easy to get at on top of it.
I was afraid I'd need a whole new master cylinder and brake booster.

ClemCLone

I should have asked earlier.
Is that what that narrow black tube goes to?
I remember a line like that when I had to remove the bellows tubes on the intake.
There was a tube-line there that I had to reseat.