Customers will feel a vibration or pulsation in the brake pedal when the brakes are applied if a brake rotor is warped. If this symptom exists, check the rotors for runout and parallelism. A warped rotor should be replaced and is often caused by improper tightening of the wheel lug nuts. In fact, uneven lug nut torque can cause a pulsating brake pedal. You should be aware that pedal pulsation is normal on vehicles with antilock brake systems (ABSs) when the ABS is working.
With a spongy pedal, you'll probably feel the need to pump the brake pedal to get good stopping ability. The complaint may also be described as a soft pedal. This problem is caused by air in the hydraulic system. Although bleeding the system may remove the air, you should always question how the air got in there. Check for leaks and for proper master cylinder operation.
The driver's complaint of a hard pedal normally indicates a problem with the power brake booster. However it can also be caused by a restricted brake line or hose. Carefully check the lines and hoses for damage. Feel the brake hoses. If they seem to have lost their rigidity, the hose may have collapsed on the inside and this is causing the restriction. Restrictions can also be caused by frozen caliper or wheel cylinder pistons.