My brakes got spongy and then pedal went to the floor. When I checked master cylinder there was no fluid. I filled it and the brakes (Only the front brakes are hydraulic) worked great during a 16 mile trip I took. When I got home the master cylinder was empty again. There is no fluid on my garage floor and no leaking you can see when car is running. If fluid is leaching from the master cylinder, could it empty itself in 16 miles with brakes still operating perfectly? Is my problem the master cylinder? I have a shop visit scheduled next week, but I’d like to have an idea what’s going on before then. Any thoughts?

 

Could be leaking inside the car from the master? or into the power bake booster if it has one..

 

No power booster. But I never thought about checking inside the car. Will explore that in the morning. Update: I drove it 100 miles today and the fluid level dropped maybe a 16th of an inch. And the pedal has been perfect since the first refill.

 

soooo strange!

 

That Fluid has got to be escaping someplace !!!!