Your adjusters should turn more than 1/4 turn. You will need to spray the adjusters with penetrating oil and disassemble them. You may have to clamp them in a vise and use a torch to heat them before you can get the adjuster wheel completely free of the threaded part. When you get them apart, wire brush them and put a little brake lube on the threads. If you can't get them apart, you will have to buy new adjusters. They can be a PITA.