I,ve got a 83 wagon that runs smooth except in heavy rain.When I drive through a large puddle the water splashes on something on the undercarriage and for the next 10-15 seconds I hear a loud clunk (like kerlunk, kerlunk, kerlunk) You can feel the vibrations in the auto t bar. Is water getting into something in the transmission ? Runs fine otherwise.Thanks.

I suspect is is a contraction of part of the hot exhaust from the cold water, that temporarily causes it to hit the crossmember or something like that. It is fairly common and not a problem. I suggest you move to a desert region as the simplest cure, cheaper than some tranny repair for sure.