All vehicles have a weak spot. You can tell when you hit it because the hit marker is yellow like when you get a head shot. The critical systems star card for the armor class helps reduce damage taken to weak points.
The yellow hit marker doesn’t show up on GA big walkers (AT-AT, MTT, AT-M6) for some reason
Here are the weak points I know about.
AT-ST: back of crew cabin
AAT: back door panel
Tatooine land speeder: engines
little speeders/tauntaun/AT-RT: just shoot the person riding it
star ships: engines and cockpit
AT-TE: underbelly (get under there with a heavy and use your sentry. It melts them fast)