The big Ball on the master cly for brakes What is its name. Can i replace

The "Big Ball" is a high pressure accumulator for the ABS Hydraulic unit. There are specific tests to determine if the accumulator is defective or if the hydraulic pump is just not working to capacity. The piston assembly in the Hydraulic unit may also be leaking internally. Warning: Do not attempt to remove the accumulator or ANY high pressure hydraulic lines. The pressure may exceed 2500psi and can cause death or serious injury. There is an actuator piston repair kit #R4740086 and Pump motor R4509292, as well as the accumulator at your local dealership.