Worn out front or rear brake pads or shoes should be replaced urgently, it could also be that in allowing them to wear so low the discs or drums have been badly scored and damaged, and they too should be replaced, if new pads - shoes - drums or discs are replaced, you should always drive with great care for a few days to allow the new parts to bed in together (the brakes may feel a little strange at first - but should soon get back to normal) if they donīt, go straight back to the fitting station concerned and report your concerns.