Originally Posted by jbchybridrider

With anything that you can fit into a tub use brown vinegar you will be astonished by the results.
First submerge and clean over night in kero.
Second submerge in brown vinegar over night.
Third as soon as it comes out of vinegar scrub with a cream cleanser like what you use to clean wash basins using an old tooth brush.
Forth give it a good spray with water dispersant.
If you have a air compressor and gun to use between stages that helps if not thats OK.
You will be amazed it doesnt matter how rusted a component is if there's any metal under it you can 100% remove all rust the process is not harsh on the metal itself and I wish I had some more before and after pic's to show but this is all I have.

This derailer is not that bad and was an easy job the freewheel or cassette is back in use and looks like new the chain could have been done as the bike basically never ridden since new in fact all these components were easy against other jobs I,ve done.