Check for worn or loose front wheel bearings.

Replace the front wheel bearings.

Check for a broken or a sagging spring.

Replace the spring.

Check for a leaking wheel cylinder or caliper.

Replace the wheel cylinder or the caliper.

Check for warped rotors.

Replace the rotors.

Check for an incorrect or an uneven caster.

If the caster is beyond specifications, check the frame and repair it, as needed.