sanding rim to get rid of brake marks?
 

I have a grey mavic rim from the 90s. brake marks are pretty bad and have a wavey pattern. I wonder if sanding the grey
coating on it down to bare metal is okay.

Not sure what you mean by brake pad marks.

If you're referring to rubber residue left on the rim, this can be removed with scotch-brite pad (or green non-metal scouring pad generally), perhaps soften up with a rag + rubbing alcohol first.

If you're referring to how the brake pads have worn down the rim (friction does grind aluminum away over time), why would you want to grind more rim away?

Sandpaper is bad unless you have scratches perpendicular to the rim that need smoothing. No need to grind the aluminum thinner. If rims don't fail from eyelet cracking or crashes, they eventually fail when the brake-pad-contact surface gets too thin from pads wearing rim down over time. Scotch-brite pad works well to smooth and remove "foreign material" (no WMD's, sorry) stuck to the rim surface.

+1. I use alcohol and the pad method now. It removes the brake pad residue pretty good. I tried sanding the rim because that's what I did with my old arraya's but when I tried it with the new Mavics's, even with wet and dry 400, it left scrathes on the braking surface and as a result I get much more brake residue.

Scotch pad and simple green takes it all off real easy.

I guess the OP's rim had grey anodizing, that was worn down halfway by the brake pads. I guess finishing their job with fine sandpaper is OK unless you go too far.

He's talking about the wave pattern of brake wear (or brake something) that you usually see on rims from extended braking. I'd just leave it.

Yeah, I'd just leave it. The alternating color is due to the spokes pulling on the rim and deforming it slightly. The pads then wear out the high-spots first. If you sand the low spots to accelerate the wearing of the anodizing, you'll cause a greater difference between the high & low spots. Then the pads will end up wearing out the high-spots even faster.

If you're talking about black streaks left by melting brake-pads, then some solvent like acetone/nail-polish remover scrubbed with a Scotchbrite pad will work fine. Don't get any on the tyre.

Don't sand.

Scotchbrite pads and, in extreme cases, Softscrub, will make your rims shiny and new.

Bob

It looks like the grey anodizing has worn off in a "wave" pattern due to the rim being distorted by spoke tension. That's quite normal. Eventually it will all wear off. Sanding will just shorten the life of the rims.