I have a CAT D3 79u that is having problems steering. The steering valves appear to be free moving with no leaks. Stem has some wear but is within tolerance with pedal position. When pedal is pushed enough just to push in on the stem nothing happens. The pedal has to be pushed completely down to "brake" or lockup the track to turn. Sometimes after doing this I release the foot pedal and the same track seems to be locked up or braked and the only way to get it to start moving again is to either quickly depress and let off the opposite foot pedal or center brake pedal. When doing this loud screeching noises are heard.