Contributed by: withidl

CV Joint stands for "Constant
Velocity Joint" and is used when ever torque must be transfered at an angle
WITHOUT VIBRATION which must be done with the drive axles (front wheels turn
and all 4 wheels move up/down).



A "Universal Joint" is simpler, less expensive and could be used (and is on
some vehicles) but it pulses 4 times per revolution unless it's angle is zero.
The greater it's angle becomes the more intense is it's pulsing vibration
which is transmitted into the vehicle body and steering; not something BMW
wants you to experience.



The CV Joint consists of arching "races" in which ball bearings reciprocate.
These bearings and their races must be lubricated so they are "packed" with
grease which is contained in an accordian like boot which is constantly
flexing with the CV Joint as the axle turns to drive the wheels. The front
"outside" boots must flex more than the rear ones due to steering, and its
this flex which eventually fatigues the rubber boots.



The X5, due to it's all wheel drive has 8 CV Joints, 2 inboard at the
differential axles (front & rear) = 4 inboard and 1 at each wheel = 4 for a
total of 8. Because the differentials are solidly mounted the drive shafts to
them from the transmission and transfer case use "couplings" which can
tolerate very small angular mis-alignments and are much simpler in design.



You want to inspect the CV Joint boots whenever possible after the warranty is
up because the joints are VERY expensive. If a boot cracks it will throw out
the grease and worse it will let dirt in which will destroy the joints
bearings.



CV Joints are EXTREMELY tough (remember you've got 8 of them) and if their
bearings are cleaned when the boots crack and are replaced you should rarely
ever have to replace the CV Joint itself.



This is just one of those maintenance items you must know about if you want
minimize your expense.



Again, CV Joints are VERY expensive and their boots need to be inspected
often.