Final answer:
Technician A is correct about disc brake systems; calipers house the brake pads and straddle the rotor. Technician B's statement regarding calipers expanding the brake pads is incorrect; the calipers squeeze the pads against the rotor.
Step-by-step explanation:
Between the two technicians discussing a disc brake system, Technician A is correct. Calipers do indeed straddle the rotor and house the brake pads. When the driver applies the brakes, hydraulic pressure is exerted. This pressure applies to each of the wheel cylinders equally due to Pascal's principle, ensuring consistent force across the brake system. Contrary to Technician B's statement, calipers do not expand the brake pads; rather, they apply pressure to squeeze the pads against the rotor, which creates the friction needed to slow down or stop the vehicle.
The principles behind this are outlined in the provided figures, which describe how the driver's force on the brake pedal is increased first by a simple lever and then by the hydraulic system, and how each slave or wheel cylinder receives the same pressure due to the master cylinder exerting force, consistent with Pascal's principle.