There's a damned good reason why cheap uprights are sold cheap, it's cos their build quality is, you guessed it, cheap, you get what you pay for...
Heck, I paid 99p for my Electrolux C12, battered, bruised, and in need of some work, but with relatively little repair (fan swap, bearing greasing, replace the VGII brushroll tube & lube the sleeve bearings, hardly anything really), it works superbly, but, the cheap plastic turds I've had, no matter how many hours I put into them, they always felt "broken", pretty much cos they're built to fail so you buy another, and another, then another, ad infinitum, gone are the days of quality built products that last a lifetime (and that's a Human's lifetime, not a fruit fly's lifetime!!)...
Regardless of what I did to repair them, even that Vax QuickLite felt like it had something wrong (aside from the cheap pleated filter "bagless" design), but that's gone now so I don't have to bother thinking about it, though interestingly, the brushroll bearings from a Hoover PureFail or similar (Dust spewer, I mean manager?) fit the brushroll of the Vax, so, I saved money there by using the bearings I saved from my PureJunk's brushroll, getting rid of that grinding rumble...