Hi Susan. There is no worse feeling than the feeling you get when you find that you've been seperated from your hard-earned money by a company that markets a product with glowing phrases of what their product can do...And then doesn't deliver on it's promises. Kitchenaid mixers can make short work of bread dough NOT! My Kitchenaid HD Pro (475 watts) self destructed after only 30 uses of making my Sourdough Bread. The problem? A cheap piece of plastic that takes the stresses of two important shafts in the mixer. Cheap, shoddy parts in a mixer you paid top dollar for. Kitchenaid shows no shame in doing so.
What is happening with your mixer as it tries to mix your dough is that the head unit is thrust back and forth and side to side (bucking). Eventually hinges become loose and sloppy. Kitchenaid's behaviour is legal and beyond reproach, so make your next mixer purchase an informed one.
and do a search for your Kitchenaid model. You'll notice that you're not alone in your mixer troubles.
I solved my mixer problems by buying a used Hobart 20qt. Commercial mixer (A200) and rebuilt it. When mixing heavy dough you should only use about 60% of the bowl capacity. less, if your mixer is agonizing with the amount of food in the bowl..
You will be able to replace the thumb screw. Be prepared to wait for at least a month for the part to arrive once ordered.
If this solution has assisted you, please rate it. Good luck! ricardok45