Dishes not getting clean

I asked my husband if I ordered the parts would he change them for me, and when they arrived, it looked so simple I did it myself. I removed the washer arm by unscrewing the disk that holds it in place. I took the metal heat deflectors off the old arm (they just easily pried off) and put them on the new. I lifted off the large round "plate" that the arm rests on and cleaned the underside. Then put it back together in reverse order.