leaking break fluid on the rear weel side of the system... where?
 

Hello,

Coming back from a couple of weeks oversea, I discover that my break fluid reservoir is empty (on the rear side, there is still break fluid on the front side of the reservoir)....

it looks liked it leaked all by itself!

I refilled the reservoir, blead the rear breaks, and then tried to push on the break pedal... basicaly, you can feel the pedal going slowly in as you press on the pedal. making me think that fluid is beeing pushed out of the system...

I had someone press on the pedal while I looked at all the connection points that I could see: rear wheels bleading screws, break fluid fluid intake, connection with the flex pipes (which are new). I also looked under the bonnet, no fluid coming out of the master cylinder or master cylinder connections. the master cylinder is itself new (<5K)....

any idea where the hell the leak is? and how to get to it? I can not see any evidence of leak under the car (I refilled the reservoir, so if it goes back down again, I will be able to double check)....

cyrille, 1980 911 SC targa, 3.0.

It might be going into the vacuum pod for the power brake such as your brake master cylinder is leaking into the pod.
There is a vacuum hose going to the pod toward the centerline of the car but I cant remember how close it is to the bottom to be able to check if there is fluid in the pod.
Bruce

that is why I replaced the master cylinder in the first place
 

hello,

This possibility was the reason why the master cylinder was replaced, the master cylinder is brand new, so I do not see why it would bee leaking...

in additon, it's only the rear system leaking, and the rear is placed further away from the vacum pod that the front break system...

any other guesses?

I assume you've inspected the rear calipers?

-Andy

tell me more?
 

hello,

well, I looked at them, while still attached to the car.
I looked at the place where the bleeding screws are and where the brake fluid intake is and can not see any leaks...

I looked at the rotors themselves, and did not see any beak fluid there either...

is there something else that I should look at?

regards, cyrille

Just a wild guess, but is there any fluid in the vent tube attatched to the resevoir?

vent tube?
 

hello,

no, it does not apear to be any fluid there....

what was your guess? what would cause fluid to be there?

regards, cyrille

Vent tube was just a guess as you have found no evidence of a leak. From what you describe, however, I'd still suspect the master cylinder. The slow moving of the pedal could be a bad seal--even on a new cylinder and the fluid has to be going somewhere so do some serious checking of the vacuum booster and the line to the intake manifold.

Couple of basic questions;
Is the fluid in the master cylinder continuing to go down?
Did you bleed the master cylinder before installing it into the car?

blead the master cylinder BEFORE?
 

hello,

What do you mean by that?

I might have missed that step, I followed the instruction in the change you master cylinder article on this site :-(

regards, cyrille

Bleeding the Master Cylinder removes any air bubbles that would be trapped inside once the brake fluid is added to the reservoir. Some say that the Master Cylinder can be bled properly just by the gravity technique. Never tried it.
Try this link which explains the process of bleeding the master cylinder. The link says to let the bleeding lines drop off the master cylinder and watch for the bubbles. I usually redirect the lines back into the reservoirs and watch the bubbles there. In any event, this may be the reason why your brake peddle still feels mushy, maybe not.Master Cylinder Bleeding how-to

My understanding has been that bench bleeding the master is only to get most of the air out of it so when you press on the brake to bleed it you force fluid out instead of just compressing and releasing air.

With this I would think if you got satisfactory bleed results, the previous bench bleed is not an issue.

You may try checking inside the shifter tunnel. If your year has the front to rear line inside that may be where the leak is . If all wheels and hoses show no leak this would be my first suspect.
I feel bench bleeding really works best with an attached reservoir .

Eddie

shifter tunnel?
 

hello,

just 1 stupid question, how do I access that?

I only have a jack and some stands to work (no lift), and despite by best tries, I was not able to see the connector where the single rear line split for the right and left wheel. is that in the shifter tunnel?

regards, cyrille

Access to the shifter tunnel is via the plate on the top of the tunnel inside the car, just in front of the rear seats. Four screws.

Not sure how air in the master cylinder would be the source of a leak. Yes, the reservoir level would decrease slightly, then stop when the system fills. Thereafter, that's it.

There are two ways of loosing fluid; internally via a leak between the MC and the power brake vacuum reservoir and externally via the system reservoir, piping and calipers. Remove the tunnel access plate at the rear of the tunnel and take a look inside. The brake line leading to the rear brakes is in there. Remove each wheel and inspect the brake calipers and hydraulic tubes and hoses leading to them.

The first diagnosis step is a visual inspection. E.g. Get on your hands and knees and look for a dark fluid area behind each wheel. External leaks should be quite obvious.

Sherwood