not hard to mess up at all but what always happened to me is I'd put everything back together and button it up and relize that I forgot one little check ball that sits deep inside the tranny so I'd have to tear it all apart again. I've rebuild like 15 in the last year, random muncies and fwd trannies and only one broke down and that was because he was hot rodding a 91 ford escort around and blew the dif pin out the case and he tried to blame it on me