Linking back to main site from seperate c-class hosted in same niche?

will this boost my main site rankings? medium difficulty local service niche. I've got other sites in the same local niche, my thought was to simply put them all on their own different C class hosting back link from all of them to my main site. Does this work or is it complete bullshit. I got like five sites I could link back to my main site. Each site has five pages of content. thanks for your help!

I do this on sub-domains of mine. So if my main site is "beds", my sub domain may be "sofabeds" and I will often place a contextual link back to the main site from that sub domain.

I know that G can see what I am doing but if I don't overdo it or mis-use the concept, I think I'm ok and I have been doing this in my niche for years with no penalty.