Venting old brake fluid and flushing the hydraulic system with fresh fluid is cheap insurance against needless comebacks. As explained elsewhere in this service section, opening the bleeder before a disc pad job prevents the caliper piston from pushing dirty fluid back into the hydraulic system. The dirt can easily ruin expensive ABS actuators, not to mention create costly comebacks on non-ABS brake systems.
For example, pushing dirty fluid back into the master cylinder can lead to internal leakage and master cylinder failure, brake service sources said. As the internal leakage worsens and the brake pedal becomes low and spongy, the customer blames the tech who did the work because the symptom wasn't present prior to the brake job.
Brake specialists said it's not uncommon for a tech performing a quick disc pad replacement to push in the caliper pistons and force dirty fluid into a step-bore master cylinder.
When this occurs, dirt clogs the check valve inside the reservoir, which keeps the right front brake partially applied. The result is premature right front brake pad wear and a pull during braking.
Technicians should replace brake fluid at the intervals listed in the owner's manual. Sources agreed that when specifications aren't available, 24 months is a good rule-of-thumb interval for changing brake fluid.