Re: brake lights

Posted by BH On 2008/7/10 8:06:42

The fill cap is vented to atmosphere. Later systems (typically, dual-chambered master cylinders, starting in the late 1960s) had a cap/cover with a rubber diaphragm to seal the fluid reservoir from atmosphere. Still, I've read that glycol-based fluids (DOT-3 and -4) can draw moisture (albeit slowly) through rubber hoses, seals and membranes. As such, it's best to drain refill and bleed the systems using these fluids every few years.