I have a Chevy Volt that I've been fixing up, and these things barely use their brakes. It sat for a few months before I bought it, and the rear rotors rusted to the point that I'm having trouble cleaning them off with my usual technique of "drive it and jab the brakes often." It still makes horrible grinding noises from the rear and the rear rotors are visibly rusty. There's plenty of pad left. Is it worth doing a more aggressive clean? If so, what would the hive recommend? I've heard of using a flap wheel on a grinder, how does that rate?
In reply to dculberson :
I generally use 80grit on my palm sander with good enough success. Doesn't fix pitting of sitting for years, but heavier new rust it cleans up well enough to finish up by driving it.
Jack up the rear, spin the rotor using a hand drill with a wire wheel or rubber eraser wheel touching the outside and use a piece of sand paper or similar to break it down? Or just use the wire wheel on the rotor to clean it and spin it at the same time?
Would evaporust work or would that yield them as inoperable as "brakes" ?
I think people used to take rotors to the shop to have them resurfaced on a brake lathe back in the day.
If there is persistent grinding however, are you sure that the pistons actually retract? Maybe stuck slides on the calipers?
Put the rotor on a drive axle, jack the car up, and let it idle while holding sandpaper against the rotor. Has worked well for me. The Volt might get freaked out though, unless you can disengage traction control.
+1 on making sure the rear calipers are actually doing anything. If they're super rusted too your driving and jabbing the brakes might not be doing anything.
They're not stuck on, the grinding only happens when coming to a stop.
In reply to dculberson :
Might you have a bias problem? Meaning, are the front brakes doing too much of the work and not letting the rear brakes engage enough.
I would...pull the rear disks and do some self sanding with something like an orbital or flap, etc. I would then grease the slides to assure their working order.
I've had the same problem with my Volt. Step 1, after making sure the caliper slider pins were free (that was Step 0, I guess) was to get the rotors resurfaced on a brake lathe. That lasted a year, then the rust was back.
Step 2 was to buy these: https://www.rockauto.com/en/moreinfo.php?pk=7465512&cc=3308762&pt=1896&jsn=474
So far, so good, but they've only been on for a couple months. The other piece of advice I would give is not to overtighten the little Torx screw that holds the rotors on. I made that mistake when I put the resurfaced rotors back on, and I was getting a "swish-swish" noise from the rotors not running true. Tighten it down, and then back it off a little. Actually, if I had it apart again, I'd probably just throw that little screw away. It seems like more trouble than it's worth. Plenty of cars get by just fine without them.
Thanks for all the tips guys! I hadn't thought of using something to spin the rotors while they're on the car. I might give the hand sander with 80 grit while spinning the rotors a shot. If that doesn't work I'll step up the sander/grinder/etc. I'll also check the caliper pins.
Worst case I'll give those better rotors a shot.
Evaporust, or just recycle them.
I wouldn't use any shop that would machine a rusty rotor. The rust wrecks the cutting bits, so if they would cut rust it means they don't care about the quality of the surface finish.
Drive backwards with the brakes on???
Back in the day, rotors and drums were huge chunks of cast iron, and replacements were expensive. For $10 each you could have the FLAPS stick them on a lathe and clean them up. These days with the flood of cheap aftermarket rotors (made of much lighter castings) that really isn't the way to go. Still quite viable depending on the thickness of the rotor, but it's doubtful you have enough meat. The person running the lathe would measure the thickness and consult a book on how thin he/she could go with it without the pistons popping out of the calipers. The downside to this is that it left a pretty rough surface that felt great in the pedal but also tended to make short work of organic pads.
I just checked. New rotors for a Chevy Volt are $20-30 unless you get some fancy electro-plated, cross-drilled fancy stuff.
Just know that anything you do at home has drawbacks. Getting them functional for inspection or when you're out of cash? Sure. Making a surface that lasts? Not so much. Sandpaper will embed silica in the soft casting. A wire wheel won't likely fix the issue if it's that bad. Most of the things you do at home will end up being helplessly pulsating within a few hundred miles.... which is not terrible if you're willing to put up with it.
I'm all about saving a buck, but when rotors can often be had for a Jackson (or Tubman) or less, I don't see the need to try to GRM a solution for it.
Just checked again. The top of the line Centric electro-coated rear rotors are $24.79. I say just pull the $50 trigger.
I have a brake lathe you are more than welcome to come use.
In reply to Curtis73 (Forum Supporter) :
And that is the other reason we don't machine rotors, our labor rate is $121/hr and you can buy new rotors cheaper than machining the old ones, if there is even room to machine.
And then one of the calipers hangs up or something and you have to warranty the pads, and it has been a year or more so the rotors have a huge rust lip at the edges, at that point you can either replace the rotors at customer expense if you'd machined them the first time (upset customer) or you can warranty them out.
So it is not only cheaper to replace than machine, but leads to better customer service during the warranty period.
In reply to Pete. (l33t FS) :
The cutting bits are so cheap I can't say that really matters to much. I have had to save rotors on various thing I have worked on that you can't walk into a store and buy rotor for. Normally my go to is hit them with a whiz wheel to knock off the rough stuff and then turn them.
Also the amount of new rotors we have seen that needed turned out of the box is pretty impressive recently.
In reply to Pete. (l33t FS) :
OK, please forgive me for the waste here, but Pete, Curtis, and Obsolete have convinced me that it's a better idea to replace them. I have ordered the coated Raybestos rotors and will report how they work out for me.
FWIW, a while back a reader called out the rusty rotor hats on the Miata. Really? Okay, fine, yeah, they could have looked better.
Tim McNair, our detail expert, shared some tips to pretty them up but, in the end, I ordered fresh Centric 120-series rotors from Tire Rack. The old ones were 20+ years old, too. 
I have access to a brake lath. I turn them when they are in spec. Just knock the rust off with a wire wheel or a scotch bright wizzer and spinning them up. Never damaged a cutter and get a finish that is arguably better than the out of the box new ones. New are nice but if things are in spec turning a set to refresh them is the best form of recycling out there. In terms of cost if a set can be had for $50 it is cheeper to get new. Turning a pair including pre sanding to remove rust can easily take a half hour for a pair.
