Matt Cutts of google explains in the video below about the myth of loss of link value (juice) passed via a 301 redirect.
Firstly what is a 301 redirect?
A 301 redirect is a signal sent by your web server via the header of a page to say “this page have moved permanently”
Why would you use a 301 redirect?
Page A has no use to users due to it being duplicated somewhere else or the product has been updated with the latest version but the old page still gets traffic and internal/external links/bookmarks. By adding the redirect you are directing users to a current and valid page.
The video is short but worth a watch.
The myth mainly came about when people 301’d a page and saw the rankings wouldn’t completely pass BUT the main reason for this myth is it would take a while for google to recalculate and pass the value. The theory was that the full value was never passed however Matt goes on record to explain that the value is the same a 1 link on that page.
It’s worth considering the page you are 301’ing is very likely to be more than 1 link so you “should” see a loss in value to the pages that are linked but not 301’d as you can only 301 to a single page.
Here at ripplegen we have worked on millions of 301’s in areas of redesign, re-structure and removal of duplicate content. Contact us for more information