Leak between Brake Booster and Master Cylinder?

[da7]

hi guys, so after I've replaced the brakes, bleed the system and topped up the fluid, (about 18 hours later) the next day the brake warning light came on, found out I'm low on fluid, not thinking about it too much I've topped up the fluid again, until that night (6 hours later) the brake warning light came on again... when i got home I also found a small puddle in the location where the front-middle of my car were...

Now I notice there seems to be signs of fluid leaking between the master cylinder and the brake booster... is it common for the seals to go bad and leak here?

The speed that I was losing the fluid seems to be pretty fast too... although I've cleaned it up, I was driving the car again (24 hours since the last top up) the light still haven't came on, and there's no more puddle of brake fluid... 2 hours later I got home, still no brake warning light... so somehow the leak seems to have slowed down all on its own?


Could changing the brake fluid from the old stuff to the new Super DOT4 start a leak? Like the way synthetic oil starts a leak?
Also the previous question, has anybody had a leak at this location on their cars?


pictures attached, although I've cleaned it up before I took the photo...

[jimmy57]

Pull the check valve out of the booster, the white plastic fitting where rubber hose attaches, and then use a wire tie as a dipstick to check for brake fluid down in booster.
You may have a leaking master cylinder and fluid is being sucked into booster.
The brake fluid may be up to the level of the check valve and brake fluid being pulled into manifold and burned in engine could make for rougher idle.

[da7]

hi jimmy57: thanks for the quick reply.... I'll check it tomorrow, it's raining badly outside... so I assume there should be no brake fluid in that hole at all right?

anyway today I've started up the car again, no brake warning light, but I thought I'd check the fluid anyway just in case the sensor is jammed/faulty... looked at the front of booster, and there was 1 line of dripping brake fluid on the face of the booster (compared to 3 lines when it was leaking worst)...

so based on my observations, since on the first day the brake fluid was leaking overnight without me driving or any brake pressure applied, and mysteriously the leak of the fluid have slowed down in the last couple of days, I am suspecting the leak would be slowed down by having the lid on tighter, and I also think I know where it's leaking, so tomorrow I'll clean the area up again, and remove the lid, just to see if it would speed up the leak and find out where it's leaking...

[toolmanjsp]

Hi da7-

Haven't had it happen to my volvos yet but I've had it happen same way on other cars, rear piston seal of the master cylinder gives away and it leaks between the booster and master cylinder. I don't think so much the type of fluid you went to caused it, but probably the fact that you changed it caused the leak because I assume you bled the brakes by pumping the pedal.

In an old master cylinder, especially one that hasn't seen the benefit of a regular fluid change, a "crud line" develops where the master cylinder piston stops its usual downward travel, normally well short of full travel (pedal hitting the floorboard). Could be when bleeding and pushing the pedal to the floor that this "crud line" damaged one or more, but definitely the rear-most piston seal, resulting in the leak you see. It looks like it may have been seeping for a while, as you know brake fluid is an effective paint stripper and the area on the booster canister below where the cylinder joins it is rusty. That didn't happen over the past couple of days.

I think it is unlikely the fluid got into the vacuum booster, not saying impossible but I've never seen it happen. There is a cavity between the back of the master cylinder and the diaphragm of the booster with no sealing between the two, that is where you see the fluid leaking out. If you had a vacuum leak in that area that could pull in that fluid then you should have noticed other symptoms such as hard brakes (poor booster performance) or engine issues associated with vacuum leaks.

BTW, I've seen new leaks develop when re-compressing caliper pistons on cars with neglected brake hydraulic systems. No leak before but leaking afterwards, most likely from forcing the caliper piston sealing rings past that line of debris that accumulates in the piston bore.

Of course with your leak a new or rebuilt master cylinder should fix it. You can probably even rebuild it yourself with a rebuild kit so long as you can clean piston bore really well.

Jeff

[da7]

hi Jeff, thanks for the reply... but I've got a question, say if the seals were leaking on the piston in the master cylinder, looking at the picture of the master cylinder below, wouldn't the fluid end up leaking inside the car rather than as a puddle outside the car?

[toolmanjsp]

Hi da7!

As leaking to the inside the cabin? No, don't think so. The vacuum brake booster sits between the cabin and the master cylinder. In order for brake fluid to get into the cab or interior of the car it would have to travel through the vacuum booster which is likely impossible.

The vacuum booster is nothing more than a diaphragm sealed in a housing with the pushrod going directly from the brake pedal lever through the diaphragm and into the center of the master cylinder piston. When you step on the brakes the pushrod works some kind of valve inside the booster and the vacuum ported to the forward side of the diaphragm helps push (pull, actually) the pushrod into the piston of the master cylinder, making it easier to brake.

If you unbolt the master cylinder from the vacuum booster you will see nothing more than a cavity and a pushrod sticking out. On some boosters I remember seeing an indent pressed into the booster housing specifically to make a drain passage for that cavity between the master cylinder and the booster.

Point of it is you have fluid leaking between the master cylinder and the vacuum booster because you can see it running out between the two. The only place it could be coming from is the piston seals of the master cylinder, and the only fix is to rebuild or replace the master cylinder.

Unfortunately hydraulic components do not fix themselves or get better with time!

Jeff

[da7]

thanks Jeff, I get it now, I got confused because I never knew how a booster worked, and that is probably the only thing I never got around to finding out... therefore I had the false idea that the master cylinder goes through the booster and are physically/directly connected to the back of the pedal, ie. similar to how the clutch master cylinder is... :O

I haven't had chance to check the leak today, but the warning light still haven't came back on yet since the last top up, and I drove about 50km today, will have a look tomorrow... but I think your analyse is correct in saying that I've damaged the seals while bleeding the system, as the timing of the incident seems just right.... thanks again...

btw, where do i find a rebuild kit? I think I should be able to replace a few seals and clean some pistons with steel wool....

[toolmanjsp]

Hi da7-

Its been a few days.. I may take back (a little bit) my statement that hydraulics don't fix themselves. Since your leak has slowed maybe it was just some junk that got under the lip of the rear piston seal that has since cleared itself out. Still, it may have damaged the rubber some and should be changed.

Frankly I don't know where to get a kit for an ATE cylinder without searching, but I imagine you can find them online. Usually the pistons and seals come new and already pre-assembled, along with a new buffer spring and maybe even a new snap ring. Just clean up the old cylinder, lube it all with brake fluid and carefully put it all back in.

I don't know if I'd recommend steel wool for anything automotive except cleaning white walls (!), it always leaves pieces behind and you don't want hard pieces of steel floating around in the brake hydraulic system. What I use for cleaning almost everything is Zep purple industrial cleaner, home depot or lowes sells it by the gallon... But careful because it etches aluminum if used full strength, so cut it about 50%, wash it all quickly, scrubbing the cylinder bore with a small bottle brush, rinse very well with hot water and let it dry. Works good for the reservoir too, just fill it halfway with the cleaner mix and shake it for a while and then rinse the heck out of it and let it dry thoroughly. Good luck! Pay my way to Oz, and I'll make your brakes like new . One place in the world the shipping business hasen't taken me to yet!

Jeff

[da7]

haha.. thanks for the offer Jeff, but I think that will cost a bit too much just to fix the brakes...hehe... but yeah I've been busy too... so haven't been working on the car much, but surprisingly the brake light never came on again, and I think the leak have stopped completely, as the area have since became completely dried, next time I bleed it, I'd want to try the pressure bleed system instead so I don't run the risk of disturbing the seals as that's probably what I did last time... but in the mean time I think I'll just leave the master cylinder as it is as I think I've got other problems to deal with in the car...