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301 redirects can pass some link value, but some of the link value will get lost.  Also, unless the old sites are topically similar to the new site, Google may not pass any link value at all. If the sites are related to your new site, try including a couple of links from your old sites to the new one.  Write some new content for your old sites that's topically related to your new site, and include some in-context links.