you are supposed to put a NEW CV joint assembly and fill it with the correct amount of CV joint grease.
Do not fill with rock hard lithium soap grease that you buy in a tin, CVJ grease is like a gel and black/gray in colour. Also note that if your wheel camber or alignment is off then your car will eat CV joints (axles) every 2 or 4 months. This also includes raising the front with spring spacers - as the axles then run bent.
When they run perfectly straight they are simply turning with no load, its when the wheel moves sideways (turn) or up and down that they put load on the little spider and balls inside.