I'm always under my hood on an average of every other day-generally. Monday driving home from work I noticed my brakes seemed funny-too much to the floor travel. I got home and opened the hood. I opened the master cylinder cap and peered inside. I looked all the way to the bottom. I was speechless. Now I'd like to start off by saying that I'm no wet behind the ears throw back. I've rebuilt & replaced wheel cylinders. Changed whole brake fluid lines-THE WHOLE KIT AND CABOTTLE!
Where did it go? No leaking resevoir. No loose cap. No wetness at the power booster side. No wetness/leaking under the foot feed (inside firewall side). Lets see?--no leaking at the wheel c's-no snagged brake lines from under the vehicle. The tires aren't wet. No wet pavement on the ground. Isn't leaking while I'm driving. Weird-just weird. Has anyone else experienced this?

 

Is it being sucked into the vacuum line through the booster?

 

I suspect sabotage. Does anyone have a large insurance policy on you??

 

Great opinion, but the booster works off of the vacuum supplied by the engine. The booster is as dry as a bone. It has been 2 days and no repeated loss yet. Some sort of a hiccup I guess. I'll keep looking and will post when I find the culprit. I appreciate the help though.--Boz

 

I had a similar "phenomemon" on a different vehicle. I finally traced it to a seal leak on the master cylinder. The fluid was leaking inside the cab. I know you said you checked it but in my case it took me a while to inspect far enough down the floorboard to find leaking fluid. It wasn't obvious at first until I pulled the rug back a good ways. I don't know if the mounting is similar on an Aero to allow this to happen, but check the inside really well.

 

well.. i suppose if your brakes are really worn out it could be just in the lines... but i'd suspect a leaky MC

 

I had a leaking proportional valve "O"seal. Every time you pump the brakes about a teaspoon is leaked out of the accumulation chamber (one end where the 7/8" flat looking bolt head is).

The o seal costs 25C.

 

I'll go out on a limb here and suggest one of your bonded brake pads fractured, sheared off the major portion of the pad, leaving only a residual layer. That would definitely drop your fluid level but probably not to the point of being completely empty.

On some long forgotten car repair column with a similar brake fluid disappearance, the culprit was a leak into the vacuum booster as suggested earlier. The fluid was being held in the bottom of the booster can. It was being sucked out along the actuating rod and thus left no visible trail.

 

Thanks for all of the good advice. I'll get up and around tomorrow and really get into it. If I haven't found it by 2morrow afternoon I'll have the wifey get behind the wheel and go through all of the different scenerios with me as if she was driving: applying the brakes and so forth as I'm sniffing around my van. I should have a better look at it that way in the event it is one of the ghost problems that only crop up when your behind the wheel. I'll keep you fella's posted. Thanks again-Bozzy