i mean do they go in and out like a strut or are they just one set length?
there's a reason chandar USED to be a mechanic. the outer joint on a half shaft is called a cv joint, and the inner is a tripot. The outer joint is stationary and is held in place with a snap ring. The inner joint is flexible and can move in and out of the inner tripot housing. They would know this if they have ever taken apart a gm half shaft. As the knuckle assembly travels up and down, it doesn't travel in a straight line. It has an arc to it. This is the reason the inner joint must be able to move in and out, however it's range of motion isn't very big. It the inner joint was not flexible in that it could move in and out, the vertical movement of the strut and knuckle would cause the half shaft to pop out of the trans.
the length changes as the wheel go's through an arc as the suspension go's up down, most cars allow for this by having splines on one end of the axle so it can slide in out as the axle length changes. much like the splines on the transmission end of the drive shaft on a rear wheel drive car
C/V Joints in long known as constant velocity joint does not move in and out like a strut/damper. It turns along with the wheel which is directed by the tie-rods. The Ball and Socket design helps it acheive this turning motion.
