I would suggest changing the transmission fluid and filter to begin with. I'm not sure which transmision is specific to this model, but if it has a "vacuum modulator" that is a part that can cause a hard thud when it downshifts for more torque. Also if you can get an OBD2 scanner capable of reading vehicle specific codes, it is possible to retrieve all stored codes. You could have a solenoid malfunctioning in that transmission. The good thing is that if that is the cause, most can be replaced without a complete overhaul.
Also please check your transmission mount to make sure it's all in tact. The stress of downshifting causes some major torque to be transfered to the mounts and to the body. You can check all bolts and bushings where the driveline is mounted to the main unibody frame. Be sure to check all crossmembers.
Others are welcome to jump in incase I missed anything.
Saturday, August 4th, 2007 AT 12:49 AM