Kamilo77

Hey fellas, did some research on my issue as follows but no luck.

So ordered a new master cylinder to fix my ever compressing pedal. Pulled out the master cylinder with no issues. Now before I just put the new one on wanted to inspect the booster.

Appears that around the MC mounting mount there was fluid that leaked down from the base and caused discoloration and corroding on the booster exterior. Also I have what appears like moisture inside the booster. Any ideas why that might occur? Does a bad MC leak into the booster after some time? The MC was in very poor condition and the fluid in the reservoir was dark.

Also, what's the best method to remove the booster from here? Thanks

jpitman2

The m/cyl usually leaks fluid into the booster interior, and some also leaks down the outside underneath, depending on the mounting used. Check how much fluid is inside by dipping a flexible tube down to the bottom of the vacuum chamber. If its more than a few mm try to get it out with a baster - the fluid sucks water out of the air and this will promote rust in the end.

jp 83 Euro S AT 56k

9two8

Interesting theory, just how do you access the connection on a RHD vac/chamber I cant even see it ?

FredR

As with most new folks to the list try advising what model you have- probably makes no difference in this case.

A servo can fail but it is quite rare- a master cylinder failure can be expected any time if the unit is old.

You have not specified what problems you had so impossible to form any kind of analysis but brake fluid running down the lower outer face of the servo will cause the paint to strip and and the servo exterior will show signs of corrosion.

The servo itself is a big rubber diaphragm that move in and out as vacuum is applied. This motion pulls on the arm from the master cylinder to increase the mechanical advantage applied by the brake pedal. Without servo effort the brake pedal feels very stiff and reluctant to depress. You can test this on a system that is working by simply putting your foot on the brake pedal and starting the car -if the servo is working you will feel the pedal go a bit soft and depress as the engine fires into life.

Sounds as though you lost the master cylinder but have read nothing that suggests the servo was suspect. Remember the arm from the diaphragm to the master cylinder is connected via a piston that has to go through a seal system- if the seal fails and you depress the brake pedal the brake fluid may try to pass through the failed face as the path of least resistance.

Rgds

Fred

Mrmerlin

OP NOTE the moisture you are seeing is brake fluid and should be removed,


Ken , you can see inside the booster once you have the MC removed.

To remove the booster the pedal must be fully depressed,
then some sort of clamping device put on the piston of the booster,
make sure to put a piece of plastic on the mating surface of the booster before clamping ,
so the mating surface is not compromised .

NOTE remove the clip from the clevis pin before you press the pedal,
then remove the clevis pin from the rod inside the car after the pedal has been pushed

jpitman2

Access to booster interior with m/cyl in place is by removing the vacuum hose from the booster body.
Its not a theory.

jp 83 Euro S AT 56k

9two8

While I agree there is a connector/vacuum line off the booster, it is,nt obvious were it is on my car ie, the elbow connection is not in view ?
Mine is a RHD car, as I guess Australian cars are too, booster mounted left side of firewall viewed from front, the only large vacuum take off disappears round the back of the booster where i think the elbow takeoff would reside ( inaccessible ) in situ ?

Mrmerlin

Ken to see inside of your booster you would need to remove the MC,
this will give you the most room to view the bottom of the booster.

NOTE This statement is true for boosters mounted on either side of the firewall.

The vacuum port doesnt offer enough room to fully inspect the booster for leaks,
unless you happen to have small bore scope

jpitman2

Yes it does look like a challenge! At least the reservoir, and possibly the m/cyl would need to be removed. If you are losing fluid and its not coming out of the calipers, the only places left are the m/cyl or the balance unit. Thick white smoke out the exhaust is also a giveaway that the booster is full, and the engine is sucking fluid in from there.

jp 83 Euro S AT 56k

9two8

Thank,s Stan, very clear..., that clarifies things a lot better.., and JP sorry if I misread your tip.

Kamilo77

Sounds like there is some fluid that seeped behind the diaphragm maybe it pools up slightly then I just have to try to shake it out. Took off the intake grommet and trying to drain it that way. Shop vac didn't do much for me.

jpitman2

9two8 - Its OK, it was meant to be generic - I hadnt actually looked at my car to see what was involved. I have seen cases where there was so much fluid inside a booster that the diaphragm couldnt move far enough to work properly - VERY hard pedal, but completely ineffective.

jp 83 Euro S AT 56k

9two8

..., cheer,s jp, it,s just that I became a little paranoid about the B/booster and the fact that I found a little " misting " on the back of the pedal rubbers a while back. A local independant Porsche specialist assured me at the time that this was quite normal, and that I had never had any reason to look/feel behind the pedals except a bit of a clean in 23 years.., and as he said, if that slight "mist" is all that developed over that period then it should,nt be of concern bearing in mind no fluid loss ever.
FYI.. I cleaned the pedals about 3 months ago when I discovered this and to date they are still "mist" free.

Kamilo77

Getting really frustrated here. My original problem was that the pedal was very spongy, never really built up any stopping power, very unsafe. Also the fluid leaking down the booster appeared that the MC was bad.

Installed the new MC, what a pain in the bum, and bled the brakes farthest away to closest. Did each wheel about 5 times, and all 4 wheels were done twice. No air in the lines.

Now the pedal is EXACTLY how it was before? Is there still air trapped somewhere? I have no stopping power I can't even get up on the ramps safely without using the handbrake.

Mrmerlin

NOTE you may feel like being in a hurry here BUT take your time, slower is better.

From here this is how I would proceed.

NOTE Only use the ATE fluid.

NOTE mixing the fluids could induce seal swell and damage the new parts.

This is done via gravity. no pressure bleeder.

Fill the MC with ATE, Wait for 20 mins till the fluid works into the MC.

then one at a time, open each line on the MC about a half a turn .

Wait ,.....you will see fluid and bubbles start issuing from each bleeder ,
once the fluid is clear move to the next line.


NOTE start at the rear of the MC and move to the front.

Once you have the lines bled then open the tip and let the air out.

Get a helper to operate the foot pedal and then do the lines sequence again.
This will be to bleed the MC.
pump a few times slowly,
hold down,
then crack the line nut.

You should have minimum bubbles but possibly a few.

When the line is clear fluid move to the next, then do the tip bleeder.

NOTE if your car doesnt have ABS disregard bleeding the ABS unit.

Once done,
then move to the ABS unit and do the line nuts there till you get blue fluid clear of bubbles.
Once done then do the wheels .

NOTE open the inner bleeder first till you get blue fluid,
then do the outer bleeder.
Follow this sequence ,
NOTE its opposite what has been done,
but its also pointed out in the WSM
LF, RF , LR, RR.

It seems like a lot of bleeding and you will use most of the litre of fluid ,
but the brakes should be high and hard when your done.

Caution .... NOTE ...before bleeding I would also suggest to replace the rear brake proportioning valve screwed into the ABS unit as these always are filled with corrosion
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