I have a 2002 Bonneville in at work that bangs when shifting it in gear,it gets bad when putting it in 2nd gear.It is a loud bang when it happens.It is a good customer'* car and she does not" hot rod" it.Will do it around 45 to 50 mph.I test drove it twice and happened to me both times.Transmission fluid looks great,this is what I checked first.No codes stored in the computer too.Catalytic converter is not plugged up,checked this with a back pressure gauge.This customer is a great customer whom takes care of this car very well,not abused.Has 179,000 miles on it.I even consulted a transmission repair shop I know,said it is something inside the transmission needing a rebuild or replacement.I even had them test drive it,same results.I ended up with this one and turning into a headache.

Have to ask- how is the tranny mount? Super high failure item. Damage is internal to these, a visual check will not show the damage. I would imagine a tranny shop would of pointed this out... but have to ask.

Not a mount,I checked this out too and this is what the transmission repair shop I know has told me.Not applying a gear right is what they said.Slipped on me a little bit too.The car is worth putting a transmission in,clean and straight not all beat up