HELP!! Shifting problems; 1997 Civic DX Automatic

I've had my 1997 DX automatic for several years, and recently it has been
having trouble shifting. When it shifts (all gears including reverse) it
makes a loud thumping noise and the entire car jerks really hard. None of
the warning lights have come on, although recently I've had an oxygen
sensor replaced. My mechanic and I can't seem to figure out what can
possibly be wrong, and the problem is getting worse. I've been told to
"drive it until something breaks" or that it could be the transmission.
Has anybody else had this happen to them?? Please help!!

 

check the motor mounts. they go after a while and allow the engine to
thump hard when it shifts. check by putting it in park on a level
surface and rocking the car back & forth. you can then see the mounts
move - look for the one at the back behind the motor.

 

a couple fluid changes are probably needed.