automactic tranny's are fairly easy lots an lots of parts to keep track of though. they work off hydrolic pressure an the way they shift its kinda hard to explain but they have clutch packs alot like a motor cycle or dirt bike clutch. they have a metal disc then a clutch disc then a metal so on an so on all inside a drum with usually 3 drums (clutch packs) 1st, 2nd, 3rd, and reverse. the bands, valvebody and planetary gears come into play for how it shifts an works. but if you want to rebuild it yourself i'd buy a book on your tranny an go step by step an double or triple check your work an if you do enough of them you remember it all an take them apart an back together in like 4hrs like me with TH350's i've rebuilt around 20 of them for me my friends family an guys like my brother in law that has a tranny leak an drives with it til it slips an burns it up $$$$$$$$