8 3/4 rear clunk when brakes are applied

i am new to this site but think it can help.
i have a 72 demon 340 4 speed 8 3/4 rear with 4.56 posi. i have had the car for 6 years a month ago i noticed that when the car was moving and when i first hit the brakes i hear a loud clunk coming from the rear of the car. i have gone under and found nothing but when the car is in nuturel their is some play. also when i turn one of the rear wheels one way by hand then the oppsite direction i hear a simmilar clunk. i dont believe it is the brakes. i alos put in a new hevy duty driveshaft and u joints 2 years ago. this noise occurs when the car is moving fast or verry slow and i hit the brakes but if the car is not moving at all and i hit the brakes nothing. the centercection was replaced 7 years ago but was used and i dont know nothing about it. i think my problem is the rear but i am not sure, also if it is the rear could it be the axles? they are problly realy old but i am not sure, would it be the centercection? i dont have any m oney so i cant take it to a shop i do all my work myself but troubleshooting can be a problem for me any ideas or help would appricieated thanks
Author: admin