This is my first post so if I screw up let me apoligize in advance. My daily driver is a 1979 300SD. I changed the transmission filter and gasket but did not drain the torque converter. Now when I drive the car for about 20 minutes I get a bad vibration if I come to a dead stop and then hit the gas. Only happens when going into first gear. Once you get past first the car drives fine. Does anyone have any idea what is causing this? Am I looking at a rebuild? Please help... Like I said when I first start the car no problems. Only after driving for a while does this happen. This is why I am confused.