a few details first. Its a 1965 Ford mustang with the 289 motor and a c6 automatic trans in it. I dont own this car i just work in a mechanic shop and when ther vehicle came in it ran and drove perfectly. the customer asked me to put in the front and rear seal for the trans. so i dropped the trans and put them in put it back in only to find that it had leaks in other places(at this point it still drove perfectly). so i dropped it again repaired one of the lines replaced a small rubber hose and siliconed where the shifter attachs and the plate next to that and put in back up in there and now the transmission will rotate freely to move forward but when you try to roll it backwards its like the brakes are on, i noticed it while i was stabbing the trans the driveshaft would rotate one way but not the other which i attributed to it being in gear and went ahead and mounted it. when you shift to reverse it acts just like there is a brake help on because if you push the accelerater hard enough it will move backwards wiothout any strange noise or anything. it is the damnedest deal anyone have any insight into this problem please feel free to hit me up

 

a few updates. with motor off and wheels on ground in neutral car will roll forward but not backward. with rear end jacked up and motor running it acts as follows Park- no wheel movement Reverse- Wheels will rotate only when moderate accelerater pedal pressure. neutral- no wheel movement Overdrive- regular wheel spin(no gas needed just release brake pedal) drive- same as overdrive. Low- acts the same as reverse(have to give it gas to tturn)
also with the rear end raised and motor off it doesnt matter which gear you select including neutral the wheels will turn in opposite directions when one is rotated by hand(almost as if it is still in park)