Brake Master cylinder too full causing weird problems?

[jiggysnitz]

So for a while now it has felt like my ebrake was on when it was all the way down. I checked it made sure it was loose and it is. Today I was playing around under the hood and when I took off the cap from the brake master cylinderand the car started to roll forward slowly (almost flat ground, ebrake off because it usually holds on it). I noticed the brake master cylinder fluid was a tiny bit over the full when the cap (which dips into the fluid a bit) was off, I wicked a little fluid out and am hoping this was the promblem. Does anyone know if that could have cause the feeling of brakes being on?

 

[DSMULATOR]

When the brakes heat up the fluid needs room for expansion and such. Depending on how much over the full line would determine if the fluid is holding pressure. Check it again after a lot of braking and make sure its still at or below the max line. Otherwise, you may have a frozen caliper piston, or your e-brake cables could be frozen.

 

[Rice Over Wheat]

You are describing the brake fluid reservoir, not the brake master cylinder. And it is virtually impossible to over fill the reservoir because the rubber hat in the cap will squeeze out any excess fluid as you screw it on. This is not your problem.

 

[DSMULATOR]

If the rubber is pushed all the way back into the cap, you can easily over fill the master. Fluid expansion isn't the most common or first thing I'd look into but the fact that he said it started to roll once he popped the cap makes me suspicious.

On a side note, I would also suggest (if it isn't new) to flush out your brake fluid and replace it.

 

[Rice Over Wheat]

Who the heck would push the rubber in all the way inverted? It is there for a reason. And besides, he still cannot add more fluid than the top edge of the container or it would pour down the sides.

The master cylinder itself cannot hold more than its internal volume of fluid as it is simply a twin chamber cylindrical piston filled with caps and seals. If it isn't filled completely with fluid at all times then the difference would contain air which is a whole other set of problems.

And brake fluid is not pushed into the two chambers of the master cylinder. It is pulled in as required by vacuum as the brake booster piston retracts as you let off the brake pedal. Fluid drawn in replaces that which was forced into the lines under pressure, leaked out, or when more fluid is required as pads are worn down and the caliper pistons must extend further to contact the rotor.