Vibrates while stirring, motor seems to be moving around in housing..

it is most likely the armature. You can test the coils with a meter set to ohms. http://www.appliancepartspros.com/motor-control-parts-for-whirlpool-k5ss.html

The housing has to be worn if the bearing has play. Try a little tape around the bearing, or some thin brass shim stock. Of course epoxy may be a solution, if applied around the i.d. of the bearing seat. A little shortning on the bearing will keep it from sticking to the epoxy.

Ideally you need to fix what's bent and that normally would involve splitting the cases to get at and repair or change the speed control lever. If you don't want to do that then removing the back cover and altering the adjustments and maybe bending the switch contacts may make it operate at both ends of the speed control.

Did it start clattering before or after it was re-greased? The K5ss by Hobart is an excellent mixer and there is no reason why it can't go on for a bunch more years. First you can get clattering if the brushes are less than 5/16th inch long, But that is not usual.

I would think that the rear bearing which is in the center at the rear may be more your problem, That bearing is behind the speed control switch and behind the governor (don't discount the governor being the problem) and is attached by two 3/8th nuts and slides onto the two guide slides that hold the motor parts in place. What i have found over the years is that 1.) the studs can bend (happens but not often) 2.) the bearing which is in the center of the big aluminum housing, (Called rear bearing assembly) moves over the years and causes humming and clattering.
So what to do about it? Loosen the two nuts a turn or two (do not remove) look at the top of the the bearing assembly and you will see a metal tab (used to attach the rear cover) (make sure the bowl and beaters are not attached to the machine) now plug it in and turn it to stir speed or number 2 position, put your finger on top of the tab and press down while the mixer is running, you should hear a change in pitch, and it should effect the clattering noise, (It will go up or down, or you may hear a new noise a light humming) (The humming is caused by the armature no longer in the center of the motor field and getting to close to the stator of the motor while it is operating, when it is out of center the developed magnetic field that causes the armature to turn gives off the humming noise because it is out of center or balance) if you notice that the clattering gets louder or softer by pushing down or pulling up you have to play with it to find the sweet spot, when you find it tighten the two nuts down just enough to hold it in place and no more. It takes a while and you wont hurt the machine but never go above speed two while doing this. If that fixes the problem you may have to do it more than once as the machine continues to age or if you move the machine around a lot. the real problem is the armature needs replacing (if this is the problem). Next you may have the machine timed wrong and that has to do with the speed control switch entirely, let us know what you find if these are not the problems we have a ways to go but they are the usual culprits with your symtom.

Open up the Motor Housing and inspect the Switch Lever with Stud.
The Lower Gearcase has many depressions which allow the stud to
snap into it when the Speed Selection lever is moved. If the Stud
is worn out then there isn't much you can do but replacing it.
3184193 is the Switch Lever And Stud part number for your model.

I had the same problem. Part #25, the "control plate assembly" It has a set of points on the lower, inside. These points turn the motor on. You can watch it as you go from off to stir. If at that setting the motor doesn't start, be very careful and bend the lower point contact up just a bit. The 2 points should make contact earlier, and turn the motor on.

First disconnect the power. After this You will need to disassemble the unit by first removing the access panel at the rear of the unit. Now you can remove the siler band around the mixer. Remove this and then also remove the screws around the upper housing. After removing these, tilt the unit to reveal two more screws. Remove these and now you can remove the upper housing by lifting the housing while slightly twisting it. After this is removed you can now see the main gears and the motor. To grease the inside gears, you will need to simply move the old grease that has been moved around and put it back onto the gears. I would also inspect the grease very carefully as sometimes there can be chunks of plastic or metal in it. Whirlpool puts more than enough grease inside the mixer to last its entire life, and the only time you ever really need to change it is if your gears have been destroyed and now is contaminating the grease.Hope this helps.

Thanks

I don't know if it will work for you but move the speed lever from front to back a few times as fast as you can. This will polish the contacts. This is like the old fashioned TV tuners. People used to turn them slowly and then complain when they needed serviced every 6 months. Spinning the tuner knob kept the tuners working flawlessly for years.

replace the stir speed switch

Did you hear a CRACK sound just as the mixer stopped running? If so, the plastic transmission housing may have failed & destroyed the worm gear and the front and rear bearings and possibly deformed the bearing seats as well. It happened to me. Although these machines are marketed stating that they can knead bread dough, they can't. Mine failed 5 months out of warranty, after only30 batches of Sourdough Bread. Take the top cover off of the mixer and look for the transmission housing near the front of the mixer. If there obvious cracks in it, it is your problem.