Downshifting

I have an automatic transmission and when it downshifts it makes a loud thud and jerks the car. What could be the problem.

Might be the transmission/motor mount(s) check to see if they've gone bad.

or yo ucould not know hot to drive anr arent heel/toe double clutch down shifting. if yo udont reve the engine up before letting out the clutch you will jerk and hte enigne will slow yo udown, let the clutch out smoother to save your brakes and your hcest form seat belt bruises.

or yo ucould not know hot to drive anr arent heel/toe double clutch down shifting. if yo udont reve the engine up before letting out the clutch you will jerk and hte enigne will slow yo udown, let the clutch out smoother to save your brakes and your hcest form seat belt bruises.

***its a automatic...

i dont know much about autos but have you checked transmission fluid?

What type of car is it? (I need to figure out what tranny)

Downshifting should not be the main way to stop a car. Downshifting is used WHILE braking. You always want to do your braking in a straight line. This allows for optimal traction. If you are in the turn while breaking it will load up one wheel for traction (usually causing you to plow into the turn) You don't downshift while in the turn because this can cause loss of traction as well and cause you to spin out/loop the vehicle.