2 domains SEO link building

Question

I have 2 domains: www.my-domain.co and www.mydomain.us.

Both are pointing for the same server, for example if you run www.my-domain.co/file.html, it's the same with www.mydomain.us/file.html.

Now ... I began the SEO for www.my-domain.co, submitted in Webmaster Tools, sitemap, links etc. I supposed www.my-domain.co will rank good for my domain keywords. After 1 year I change the domain from Webmaster Tools to www.mydomain.us which has no links pointed to him, and now the question come:

If I begin the link building (dofollow blogs, formus, link directories etc.) once more on www.mydomain.us it will get double link juice?

Answer 1

What you'll get is duplicate content issues. That's not good. You need to choose which domain is your primary and do a 301 redirect from the secondary domain to the primary domain. Then you should solely seek links to your primary domain. But if someone points a link to your secondary domain it will count towards your primary domain with only a small dampening factor. This also applies to existing links so if you do switch domains the old links will still help you (minus the dampening factor).