Why do my brakes squeak?

Hi Paul, my Toyota Prado 1996 brakes are not working well. When I step on the brake pedal, it makes a vibrating sensation, a rumbling sound and becomes hard. At that point, the car takes long to brake.
This problem has been on and off but the frequency has increased yet I recently replaced the brake pads and brake discs. J. Semakula

Hello Mr Semakula, your car may have a faulty ABS (Anti-Lock Brake System) modulator. The ABS system is designed with your brake system to use wheel speed information relayed by a sensor at each wheel and a hydraulic modulator pump to provide independent braking force to each wheel.
This is crucial in preventing skidding during emergency braking on slippery surfaces, which may be caused by varying wheel speeds.
When the ABS passively engages, you feel a pulsating sensation under the brake pedal as the modulator selectively delivers independent brake pressure to avoid skidding and keep the car in line.
The ABS system can fail due to corrosion of its multiple hydraulic valves, usually caused by a delay to service the brake fluid. Occasionally, ABS is damaged by an electrical fault caused by a bad relay or short circuit due to a wrong jump starting procedure.
When the ABS is faulty, it will engage prematurely or when you don’t need it hence the juddering sensation under the brake pedal whenever you brake, even on dry firm surfaces.
It may also fail to deliver the brake fluid pressure, which is routed through it causing the stiff brake pedal and failure to brake. You need a computer diagnosis and inspection of your Toyota Prado to confirm my remote diagnosis.