What is the best way to remove rust from an item such as a derailleur which has both steel and aluminum components? I've read that OA is not good for aluminum and the same for vinegar. This part definitely needs a full soak in something that won't harm the aluminum but will take the rust. It is a 600 arabesque front derailleur and the aluminum items are pinned to the steel, no removing them I'm afraid.

I haven't had any problems throwing aluminum into OA. Clouds it up but comes right off on a wire wheel.

Yeah, as long as you don't leave it in for days in a very strong solution you might have to repolish the aluminum but it shouldn't be damaged.

Vinegar is the common name for acetic acid. Acids and aluminum do not pay well together. So go dilute, and not for too long.

Gel type rust remover from auto supply store. Syringe from craft store. Use syringe to apply gel precisely where needed. No soaking, little waiting, rinse with lots of cold water and you're done.

I've kinda done that too with a stronger OA solution...just brush it on carefully but the gel is a good idea. Wonder if you could somehow gel the OA solution?

Restoring cars, we always use phosphoric acid to remove rust. While we get it in gallon jugs from NAPA, you can get a weaker solution from your local supermarket, in the form of Coca Cola. You just soak whatever in the Coke for a few days and the rust should be a lot easier to brush off after.

Thanks guys. It looks like a small bit of the aluminum slipped into the solution last night anyway. It just seems to have brightened it a bit which is ok by me. The rest is soaking now.

Scarlson, good to see a fellow car restorer here! I use phosphoric acid quite a bit as well, but I must say that I've been very impressed with this oxalic acid. I'm trying to figure out why we car guys don't use it more! And thanks for the tip on the coke. I always dilute the strong stuff, but having that trick in my bag could be useful.

Likewise, good to see a fellow car restorer here. I'm currently working on a '65 Lotus Elan, so I've had to learn to fiberglass in addition to stripping rust from the inside of chassis box-sections. I've never used oxalic acid before, and its lack of presence in the auto community is probably why. How does it work differently from phosphoric? More aggressive?