please help : car vibrates heavily

hi , i just picked up a 74 valiant with 225 /6 automatic . i need help trying to diagnose a severe vibration problem . i am not sure if its steering suspension , brakes or transmission or other . as i have never experienced this problem before .

what happens is at first the car drives fine and smooth . then , after awhile it suddenly starts to vibrate heavily , like an earthquake . feels like its the front , but could be trans . it usually happens when i slightly decelerate or lightly press on brake pedal . but continues until i either mash the brakes hard , or pull over and park for a few minutes . and sometimes vibrates just on its own .

so far i have only greased the front end . and looked at the front brakes , everything looked ok and the drums came off just fine . though it does pull a little to one side when braking . i will adjust that , but have'nt yet . also , when i tried to back up yesterday . it did not move in reverse right away . i had to gas it a little then it finally broke free and backed up . felt like sometime was holding it up .

just wondering if anybody has had this happen to them before .

i thought maybe the wheels are out of balance and or the drum might be warped , but i don't know if that would be a constant vibration are intermittent one . or be strong enough to shake the whole car violently .

talking to a few people locally , they suggested , worn tie rods and another person said definitely the transmission . like the engine is fighting the trans or something .

anyway , any thoughts or ideas would be greatly appreciated . thanks

p.s. i will be posting this in steering , brakes , and transmission , so if you see it there to , its the same post .