Quote:
Originally Posted by brshap
A vent (whether a cap or vent like on the 911) is necessary because the volume of the system changes as the brake pads wear. If it were sealed the increasing volume due to wear would create a vacuum in the system.
|
^^ +1000 This. They're all vented
AFAIK - unless they've started doing something funky on those modern vehicles.. Most older caps are pretty obvious - little hole in the top. Some are more discreet - but they've got to equalize the pressure by allowing air in both directions.
Then consider both that brake fluid is hygroscopic ("aborbs moisture") and that the system is vented to atmosphere - and the reason for a regular brake fluid change interval should be clear. The stuff doesn't wear out sitting in your garage - but it does absorb moisture, every day.