I bought a spare set of rims to put winter tires on. The guy that had them let his brakes go to shit and they were grinding metal to metal for quite some time and there is a really heavy rust build up on one of the rims. I managed to get a lot of it off but there is still quite a bit there. Anyone have a good cleaner that will eat down in there and get it off. I have no dobt that it is burnt right on the paint
If it's actually rust (Fe2O3, and not something else that looks like rust), you might try bleach on it. That works great for me when I get rust stains in my kitchen sink.
Test it first - try it in a spot that's not easily seen.
If it's actually something else such as brake dust, get some wheel cleaner at the parts store or Walmart. I have some "Black Magic No Scrub Wheel Cleaner" that seems to do a decent job for me when I've used it.
I don't know what it is about brake dust, but it somehow penetrates the wheel surface and doesn't want to clean off very easily, that's for sure.
[Edit]Re-reading this, I just caught the "painted" in the title. Definitely try the bleach in an obscure spot. Maybe cut it with some water, first. Likewise, try the wheel cleaner in an out-of-the-way spot as well.
I could see strong solvent marring the paint.