Brake fluid in driver's footwell - Master Cylinder leak?

[Nickshu]

Today I noticed a bit of brake fluid had drained onto the driver's floormat and when I looked under the dash it is running down the heating duct above the clutch pedal.

I looked around the master cylinder in the frunk and there is a bit of fluid there.

I recently bled my brakes, first via a Motive bleeder, then via the two person pump method to "exercise" the pistons on my newly rebuild calipers by PMB.

SO.....is my master cylinder leaking or is this from the brake bleeding process? It doesn't seem normal for the M/C to leak during any bleeding.

Thoughts??

[Rod Schneider]

Sounds like the master cylinder is leaking.........
Wouldn't be the first time one started leaking right after a brake bleed. During bleeding, the seals in the master cylinder can get damaged when the brake pedal is pushed all the way down as the bleed valves are opened.

[MysticLlama]

Had the same problem, right after a motive session also.

Was the two short hoses that connect the master to the reservoir, I'd carefully look those over first, much easier fix.

[Nickshu]

Originally Posted by MysticLlama

Had the same problem, right after a motive session also.

Was the two short hoses that connect the master to the reservoir, I'd carefully look those over first, much easier fix.

I just replaced those hoses, but wondering if it was leaking from the rubber seals where they connect to the M/C while under pressure from the Motive.

[trak ratt]

Could also be from the overflow hose. Did you clamp it off? There's a junction on the left fender between the hose from the reservoir to the dump tube. If it comes loose the fluid can run down inside the car.

[Nickshu]

Just removed everything in the way of seeing the M/C. It's leaking from the rearmost reservoir hose/nipple rubber seal. Pedal feels fine and brakes function perfectly otherwise, so the M/C itself is fine.

Anyone replace the rubber seals on the two nipples on the M/C? Is it possible (and easy) with the M/C still in the car? It looks like the rubber seals and nipples should just pull right out.
I seem to recall reading an old post saying this was difficult with the M/C in the car...????

[Nickshu]

Just to follow up, today I installed new master cylinder rubber seals and reservoir hose nipples. It was not a difficult job at all. I clamped off the reservoir hoses with a needle nose vice grip and cut the hoses below it (packed the area w/ paper towels. Removed the reservoir and drained. The old nipples and seals pulled out easily with long needle nose pliers. New ones slid right in with a bit of effort (and a touch of brake rebuild grease/lubricant). The old seals were in bad shape, especially the rear one, which is where the leak was coming from. I put in new blue hoses cut to spec (120mm and 65mm respectively) and filled very slowly with fluid so as not to trap any air. Test drove, no leaks and no bleeding needed.

See the photo of the seals below. The one on the right was the rear one.

[Porsche84]

The problem with the Motive bleeder is that the reservoir is too full when you are done bleeding. Too much of a coincidence to have the master cyl or rubber seals fail just after you bled brakes. My bet is you overfilled the reservoir and it is just showing up. FWIW, brake fluid on your shoe soles is very slippery and dangerous if you foot slips off the brake when you need it.

[Nickshu]

If you follow the Motive procedure its easy to drain the reservoir down to the appropriate level before detaching the bleeder. I think the leaking is from the pressure it puts on the hoses and seals which were designed only to withstand the gravity of the fluid in the reservoir.