When driving my 1991 Trans Am 305tpi, the car makes this loud thump, when accelerating from a stop. It is sounds like something is smashing into the bottom of the car. Any suggestions?

when was your transmission fluid changed? esp if it was an automatic. clutch pack could be slipping.

also, check mounts.. engine & tranny should not move much. 1" is acceptable.

car is automatic, mounts are good, transmission fluid was changed recently. car has a total of 138,000 miles.

Transmission mount on cross member(at tail shaft) is probably bad. It may look ok but I would remove and inspect. Very easy to do. They are known for going bad. Good luck

hahaha.. I know that sound all too well.. You broke your transmission mount. You will need to change it.. I used to break mine all the time. Put too many people (weight mostly) in it.. And it will break it..

That's the funny thing, I never have anyone in the car other than myself, and one passenger, but thank you all for the answers.

Yeah.. I was mostly speaking on myself with the passenger load thing.. I had an 85 camaro and an 89 GTA trans am. Funny thing with those cars is that the passenger weight is like 450lbs. Two normal sized guys and a speaker box in the back pretty much taps out the max weight. And that is on a new mount driving like an old lady (no offense meant). I ended up putting a poly trans mount and it solved the problem of breaking the mount.