1. New pads need to seat into the rotors before they come into their best operation. Machining the rotors or at least scuffing them up with a sanding disc cam help make this faster, but it doesn't do away with the need to seat them in.
2. You may need to bleed the brakes to make sure there is no air in the system.
3. You may have installed the retainer clips improperly. This is a common mistake with results like you are describing.
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