88 4x4 front diff trouble

Ok, Transfer box works fine, front diff wont lock, took off the stupid diaphram, tried to engage it by hand and it would only move maybe an 1/8 of an inch, i dont think it is enough to engage it, seein git has to move the collar over the splines. what would be my first action here, do i need to pull the diff, or what, any and all opinions would help, dont want to do double work for no good reason, thanks.