Join Date: Jul 2003
Location: Memphis, TN
Bronco Info: '83 VIN & title on '93 frame/body w/'95 4.9L & EB paint
DOT3 brake fluid is EXTREMELY hygroscopic, so it's NOT vented. Of course, there's a safety release like the A/C system has, but that doesn't qualify as a "vent", either.
As fluid moves into the calipers due to pad wear, the diaphragm in the cap follows the fluid level down, maintaining a seal between the outside air & the fluid. When you compress the calipers, that fluid moves back to the reservoir. So as long as you have NOT added fluid since the last pad change, it won't overflow the reservoir.