The Greatest Shopvac emitted an intense smell of electrical death while inhaling fuzzballs from the Basement Shop stairs, prompting me to tear it down. For the record, it’s a Genuine Shop·Vac QSP 10 (Quiet Super Power):
Removing the handle and upper plate reveals a slab of (presumably) sound-deadening foam over the motor cooling fan. As far as I can tell, the last job this vacuum had before the previous owner discarded it was inhaling drywall dust without a filter:
Flipping the motor assembly over and removing the bottom plate revealed a pair of equally solidified foam slabs baffling the main exhaust path:
They eventually became Clean Enough™ after protracted rinsing, so maybe the thing now runs as quietly as the name would lead you to believe, if you believed in names.
Disconnecting and extracting the motor revealed the razor-sharp impeller disk. A shop rag prevents lacerations while torquing off the nut holding it to the shaft:
Rust on the washer below the impeller, along with the layer of caked white cement, suggested water accompanied the drywall dust:
Gentle suasion from the Designated Prydriver eventually eased the washer off the shaft and freed the motor:
It’s an old-school series-wound brushed universal motor. The plastic plate in the middle of the picture has a helical spring pressing the carbon brush against the commutator:
The rotor turned … reluctantly with the brushes in place and spun freely without them, suggesting the horrible smell of electrical death came from arcing across the gunk accumulated on the commutator:
Many iterations of diligent scrubbing with denatured alcohol on cotton swabs and old t-shirt snippets got rid of the crud, although that commutator will never look all shiny-clean again:
At least the brushes aren’t glued to it!
Reassembly is in reverse order, although I took the liberty of splicing a few inches of wire into the switch leads, because I’m not working under factory conditions with all the proper assembly fixtures:
The motor passed the smoke test and no longer smells like death, so it’s at least as good as it ever was.
It may run quieter with clean foam baffles, but I still turn off my power ears or don hearing protection when I fire up any shop vacuum.
The Smell of Molten Projects in the Morning 
Emery cloth may be applied to the commutator. Follow up with a pointed tool to clear debris from the grooves, then a blast of compressed air.
The commutator /still/ won’t look new but it will work like new.
Make sure the brushes move freely in their respective spring-loaded housings. Gunk builds up everywhere!
Put a drop of light machine oil on the armature shaft bearings. If they have felt reservoirs, put a drop there too.
Much to my surprise, the rotor turned freely, so I defined the bearings to be Good Enough™, particularly as there was no good way to pull the stamped aluminum fan off the shaft.
Next time, fer shure!
Brochures for my early 70ies Emco lathe showcase a guy refinishing a commutator, so there was a time when that was a thing. Trying that trick nowdays might end up in tears as I suspect the bars got thinner over half of century of “product optimization”
I vaguely recall specialized commutator refinishing lathes in car repair shops, back when cars had DC generators rather than AC alternators. Maybe I’m thinking of the same illustration you are!