where is my brake fluid going?

[92EcoDiesel Jetta]

92 Eco Jetta. Brake reservoir gets low every 2 months or so and I top it up. Must have added more than 2 qts over the last year or so. No leaks anywhere on the brake system that I can find... all dry. I suspect it is leaking into the booster. Anyway I plan on pulling the master cylinder and booster and have a look but want to have a master cylinder on hand if needed.


Anyone have experience with the KMM unit https://www.fcpeuro.com/products/vw-brake-master-cylinder-357611019bec?gclid=CjwKEAiApOq2BRDoo8SVjZHV7TkSJABLe2iD0O1t9ca3IqBfhh4e045ldQMDJkIlMDYqVRP6016hbRoC8TDw_wcB


An ATE is spendy more than 3X the KM https://www.fcpeuro.com/products/vw-brake-master-cylinder-cabriolet-jetta-golf-357611019

[vanbcguy]

Clutch slave cylinder is another possibility...

ATE is good stuff. For what it takes to yank the MC from the booster I'd do it first for an inspection rather than buying a quality part you may never need, or buying a cheap part just in case. The KMM one is probably serviceable but you probably would never have to replace the ATE one for the rest of the time you own the car as long as it receives good clean fluid.

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[theman53]

I had that issue, ended up 2 faulty master cylinders. They leaked into the booster. FWIW the booster worked fine it was just full of fluid.

[92EcoDiesel Jetta]

I had that issue, ended up 2 faulty master cylinders. They leaked into the booster. FWIW the booster worked fine it was just full of fluid.

Was this on the MK 2?  How much fluid can the booster hold? How did you clean it?

[ORCoaster]

I think if you look back with the search function and use his ID and a subject like brake booster you will find his entry.  I think he more or less took it off drained it, dabbed it out and rinsed it with some solvents and then soap and water wash.

Is that about right 92Eco?

[theman53]

I dumped the booster as it was rusty on the outside and a great guy gave me a new one. If I were to have kept it I would have siphoned it out and ran it. I do not think the brake fluid hurts it at all.

[fatmobile]

I'm thinking the later Rabbit and MK2 resevoir leak down the front of the booster instead of inside it.
You would see it.

Which compartment gets low? Front or back?

Leaking from inside the rear drums?

[92EcoDiesel Jetta]

020 tranny cable clutch no slave.

Leaking from front reservoir, not sure about rear. Will check.

Had rear drums off they were dry.

Front of booster is dry.

Will look closer again everywhere tomorrow.

[RabbitJockey]

pretty common to get a bad mc out of the box.  when my rabbits mc leaked it leaked down the front of the booster, but many leak inside of it.

[92EcoDiesel Jetta]

Isn't there an o-ring between the MC and the booster for a vacuum seal? If it is leaking brake fluid outside of the booster, then the vacuum in the booster is also leaking and thus not getting power assist?

[air-cooled or diesel]

if anything, your not losing boost, if anything the airflow is going into the motor, crankcase, and if air is going in, its going to back up the vent(s). you may not feel the difference in the brake pedal, and if air is moving the vac pump will suck it in and it goes in the cc. or the boost your losing, you dont feel in pedal, but its pressurizing cc? possible.
the other thing was getting brake fluid out of booster, cause they are a junglegym to get out, after 1 or two you get used to it. i find if fluid gets in my booster, i have to take it out, and use softsoap, palmolive, dawn, with warm water, swish, rinse, swish etc, on a good warm day set up in sun to dry, some compressed air, helps. (clean up threads, etc.)

[92EcoDiesel Jetta]

Took MC out and as expected the booster was full of brake fluid. I used a 3 liter wine bottle made a sucker out of it and a 12 v vac pump got most of the fluid out. The bottle is about 1/5 full, that's a lot less than the 3 x 32 oz bottles of brake fluid that I used to top up with over last year and a half. Since I do not have any external leaks, all that fluid must have been sucked into the engine! How bad is that?


Ordered a new ATE MC, hope it gets here quick. In the mean time I have not decided if I will take the booster out to wash it out. Maybe I'll just use a garden hose to flush it out in place, then suck out most of it, blow it out with compressed air and put a 40 watt incandescent bulb under it overnight to dry it out.

[theman53]

Mine actually leaked through to the inside of the firewall a little too. figured this was your issue

[92EcoDiesel Jetta]

Mine actually leaked through to the inside of the firewall a little too. figured this was your issue

I'll look tomorrow and see if the inside firewall is wet. If that is where all the brake fluid went, shouldn't my carpetting be soaked? They aren't.

[92EcoDiesel Jetta]

googled "brake fluid in engine oil" and apparently the effect is it ruins engine seals. I put in a Teflon main seal when I did the clutch a few months ago so I am ok there I think. I'll keep an eye on the other seals and see if they start leaking.