New rear rotors won't fit over rusty shields- GM trucks

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#1
I keep running into this problem when replacing rear rotors on GM trucks and large SUVs with rear disc brakes. The 'backing plates' are swollen with rust and the new rotors rub on them. Sometimes the new rotor won't even fit due to the interference.
I always get my rotors from Advance Auto. When I compare these to the old rotors, I can see that the old rotors allowed more space at the inside edge by the swollen backing plates...they were not rubbing. They may have rusted away to create the extra space, but I suspect they were machined that way when new.
I've handled the problem by filing, grinding, or removing parts of the backing plate to eliminate the interference. What do you guys do? I suppose I could get factory rotors that would cost more but bolt right on. I haven't tried other aftermarket brands...Can someone tell me if they fit just fine over a rusty backing plate?
I know you're gonna say "Just replace the shield, Dorman makes a two piece kit now." I just want to know if rotor brands other than Advance Auto's 'Wearever' have the same interference problem.
 

billr

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#2
Wow, those clearances must be really tight! I understand what you are describing, but wouldn't think a sheet-metal backing-plate could grow in thickness more than .010-.020" due to rusting...
 
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#3
Spent two removing a rotor last fall from my kids 2000 Taurus, entire inside of the rotor was loaded with rust solid to the hub that had to be slowly chipped away. Here its spring already, go out to do a brake job thinking will be done in a couple of hours, end up pulling the brake backing plates, dragging out the sand blaster, coating with high temperature paint, replacing rusted out lines, and lucky to be done a midnight.

I rarely buy from Advanced unless its late on a Sunday night, only place opened, but doubt if it is their rotors, a caliper will tell quickly if there is a difference. Super thick rust I can believe.
 
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#4
billr, the problem area has a lip folded back on itself, with a bead of sealer in the gap to give the rust something to push against. Three layers of rust stack up to cause the trouble.
 

billr

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#5
Gotcha, and I guess the lip can even unfold a bit as rust builds up in there. Still pretty close, though.
 

nickb2

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#6
@Danica, I know all about rust, and I know the exact problem you are having. I do exactly what you do! I chisel and buff away till the rust is no more, then, and only then do I have a fighting chance of that brake job not coming back for cornering noise. Sorry, no special fix from me on this one. Just a fact of the job and after market machining.
 
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#7
Could write to GM and suggest they use stainless, gee, why didn't we think about that? Let's give this guy a new vehicle for that suggestion. Or better yet, have the rotor lock up and get killed, so your survivors could sue them for several million bucks. But they will just say, that is poor maintenance, its your fault, not ours.

Could sue the state on the basis that salt saves lives, but you can't sue the government. So you just remove the part, sandblast it, paint it, and hope it lasts a couple of more years. This wasn't near the problem when we had studded snow tires, its like the whole world is against us.