simpson 605 agitator only agitates one way?

Need more info. Need full model number as there where several Simpson machines with 605 on them. Look for full number on rear of panel and is there a name after Simpson & before the 605? When it agitates one way freely then goes to reverse the agitator does it sound like it is jamming on something or is there no sound at all?

Lincoln Appliance NZ
May 2012