Which statement about hydraulic pressure is true when the parking brake is set and hydraulics are deactivated?

• A. Pressure will bleed off in the #2 system.
• B. Pressure will bleed off in both #2 and #3 systems.
• C. No pressure loss occurs.
• D. Only the #3 system loses pressure.

Answer: (B)

When the parking brake is set, the hydraulic pressure from the circuits that feed the brake is what holds it in place. If the hydraulic pumps are deactivated, there isn’t a continuing source to maintain that pressure. The braking system is arranged so that any trapped pressure from both circuits connected to the parking brake will bleed off through the brake valve and leakage paths. Because both circuits are tied into the parking brake, pressure in both will drop, leaving no residual pressure to hold the brake or surprise you when hydraulics come back online. That’s why the correct statement is that pressure will bleed off in both circuits.