i am so close to checking "bike overhaul" off my list. but the last few steps are causing me a lot of frustration.

just some background information before i start: the bike is an old Mongoose mountain bike that has hardly been rode and was sitting in a shed for 6 years. i replaced the free wheel with a 14-34T 7-speed Shimano Mega-Range. the rear derailleur i have is a Shimano Tourney Megarange, so it should be capatable. i replaced the chain but didn't remove any links because i was unsure of the length after measuring it and figured it was better to have it to long rather then to short. also, the adjusting was done while the bike was upside down. i don't own a bike stand so i figured it was the best way to go about it.

i replaced my shifter cables and their housing and cleaned my derailleur, so i decided it was time to adjust them. but i cant quite pin the source of issues my bike is showing.

When i first attempted to adjust the rear derailleur, the chain made an awful lot of noise when it was in the lowest gear and the cage was vibrating (it was in low on both derailleurs, i was not crossing the chain). so i took the chain off and loosened the anchor bolt for the cable. then i screwed the barrel adjuster all the way in and shifted to the highest gear on the rear derailleur, then pulled the cable taunt, screwed the anchor bolt back in and put the chain back on.

i went through the adjustments again and the noise seems to have improved but it was having trouble shifting through the gears when i took the bike for a ride.

what i would like to know specifically is, should the barrel adjuster(s) be screwed in all the way before installing the cable (im wondering if cable tension was the cause of the vibrations)?is it better to install a chain using the pin rather then a master-link if it ensures more precise measurement? and how exactly do you use the barrel adjusters to fine tune shifting?

im going to try adjusting it again tomorrow and see what happens. sorry for the lengthy detail, but thanks for any help guys!