why the pronounced @ loud thud when shifting into reverse

Unfortunately its a common problem with the S series. The transmissions had that problem going into 1st gear from park as well. Have it looked at by a REPUTABLE transmission shop.

if you go to the Saturn fans website there's a whole wealth of information you can get from that website its called Saturn neilla or something just look up Saturn fans website transmission issues and you'll find a whole bunch of information that could help you it's too much to list here but I believe there is some kind of condition where you can put the car in reverse already backed up against a building and it helps relieve some kind of solenoid pressure issue in the transmission but you'll find out more on that website or others take a look at them.

I have a Saturn sc2 a 2001 and I put Mobil 1 full synthetic transmission fluid in there with two flushes and two fill ups so the same fluid Mobil 1 synthetic full synthetic and my transmission runs real smooth those transmissions are a little rough to begin with so I would put synthetic fluid in there when you do the job of replacing the fluid I'll look up that website and link it on here too.

ok here's that website I was talking about they have a lot of great information about Saturn's on there enjoy hope it helps. http://www.saturnfans.com/foru ms/showthread.php?t=77671