Make sure it's level. Check the counterweight spring, #15. Sometimes the lower attachment hole rusts out. If that is the case, drill a new hole and reattach the spring. Check the three horizontal tub springs, #3. Check the alignment of the suspension plate, #17, (skate plate). Could also be a worn out drive block (secures tub to basket drive tube), severely worn or broken damper pads, #16/18, on the skate plate and/or base assembly. Could be that the metal portions that ride on the damper pads are gummed up.