if all the transmission fluid were to leak out, would the transmission not go into gear/be totally unresponsive?
if you lost as little as two quarts the transmission would not be able to maintain pressure and likely start to slip, and if you did not park immediatly and go get some fluid, you could very easily ruin the internals by trying to force the car to move with not enough fluid pressure. So if you transmission ever slips, park it, and check the fluid level, make sure the transmission is full. and go from there.
Yes, even being 2 to 2.5 qt. low will cause it not to go into gear. The auto trans works on hydo pressure and with no fluid or low level of fluid there is no or very little pressure
the fluid is what turns the transmission. without it. not only are you not going to go anywhere but it will also ruin the transmission
