it safe to use on car brake lines, my front line show a little surface rust maybe the rear lines also I haven't checked them yet?

Thank you for the question. The Loctite Extend Rust Neutralizer is a rust converter designed to stop rust, protect the surface and act as a primer for the finish coat. It converts rust to a neutral surface ready for painting. This product would not be well suited for the intended use described. Recommend you seek assistance from an automotive specialist