Drive shaft

A driveshaft is a bar to extend rotational torque.  Driveshaft is connected on one end to the transmission and on the other end to a differential (which is connected to an axle).  A it simply rotates at the exact same rpm as the output of the transmission/transfer case.
(http://www.car-videos.net/whatis/driveshaft.asp)

 Basically, drive shaft is to torque and rotation. They are different in a front wheel drive car and a rear wheel drive car.


what to do (inspect, test and mesure to assess the condition of the driveshaft)

Before any inspection, the first thing we need to do is to look at the phasing of the friveshafr. Read the manufactures specs and see if the phasing is correct or not. If not, dismantle the phasing from the shaft and put it  in the ringt way to fix.
when you check, check for cracks and corrosion by visual checking then  dissassemble them all, clean off the grime with WD-40 and wipe off the lubricated layer.