Are you sure the hydraulic motor is bad?....as it's usually a problem with a relay and/or the pressure switch.
LEARNING ABOUT THE "TEVES" BRAKE SYSTEM
The hydraulic brake booster on a late model Mark VII and early Continental is very different from most. It is equipped with something known as a "TEVES" brake system.
The main parts in the system that we will discuss include an ACCUMULATOR, a HYDRAULIC PUMP, a hydraulic pump RELAY, and a PRESSURE SWITCH. These are the key players in this operation.
THE LOCATION OF THESE PARTS ARE AS FOLLOWS:
HYDRAULIC PUMP MOTOR= Underneath the brake assembly (2 pin connector) Hydraulic pump motor
RELAY = On the drivers side strut tower
PRESSURE SWITCH = 5 pin connector facing the # 7 or 8 spark plug(drivers side)
ACCUMULATOR = Round black ball on the drivers side
WHAT THESE ITEMS DO:
HYDRAULIC PUMP MOTOR is an electric hydraulic pump used to "boost" pressure for the brake assembly. This pump is $900 new!
hydraulic pump motor RELAY is just what its sounds like. It gives the hydraulic pump motor power to come on.
PRESSURE SWITCH is the "brains" in the system. It senses how much pressure is "on line", and when the system needs more pressure, it tells the relay to "power up" the hydraulic pump motor.
Another one of its jobs is to turn on the RED BRAKE LIGHT, then the ANTI-LOCK lights to alert the driver that the pressure is dangerously low. (The reason the anti-lock light comes on, is because the ABS cannot function if there's a problem with the manual brakes)
ACCUMULATOR stores energy or pressure like a reservoir. Its there so the hydraulic pump motor only has to come on every 3rd or 5th time. Its design is more complicated, but basically the same principle as an air tank on a compressor.
WHAT NORMALLY HAPPENS:
What usually happens is, in time, the accumulator gets weak with age and can't hold the pressure like it was designed too, and therefore, the hydraulic motor comes on every time the brakes are applied....rather than every 3rd or 5th time. This means all these parts are working 3 or 5 times more than they were designed to. This puts an extreme amount of pressure on an already old system.
What we know from this is, the accumulator needs replacing because it's what started all this, but now the pressure switch and relay needs replacement also because it has worked overworked.
NOTE: always replace the relay when replacing the pressure switch. The relay came on every time the pressure switch told it too, so if one is worn out....the others not far behind!