Hello, so I'm trying to better understand failing cv joints and how it can affect front differential on a front drive SUV. I read an article that when cv joints go bad it can affect the front differential on SUV's because apparently they have a locking differential on front wheel drive SUV's. When does the differential lock up? Is it when steering stationary? Or does it have to do with something else. Also i read that steering to full lock puts the max load on the CV joint, is this damaging to the CV joint, and what are symptoms of a failing cv joint. Sorry, I know these are alot of questions but if someone could help me understand this all better I would greatly appreciate it!

SOURCE: CV joint questions

well now,,,il tell you a storie,,,better sit down?
the cv joints are the joints in a drive train that for use of a better word "bend the drive shaft" so it dont brake when you turn a corner,,,ie:parking! inside the cv joint is held on the drive shaft be some splines in the drive shaft and a spring clip holds it all together there is an "inner bell" it has normaly 5 slots in it that have big "ball bearings" in them that slid around up and down these slots on the out side of the cv joint is the outer "bell" this also has slots that the ball bearings fit into so the drive trough the cv is compleat,,,when you turn the wheels the cv joints slids round on these ball bearings twisting round but the drive from the engine is still transmited to the road wheeles trough the cv
when this cv joint starts to were out the ball bearings are pitted and not ball shaped any more and the slots they run in are not smooth that to gets pitted what happens is the cv starts to "crack" under load,,,and vibrate when turning or being driven you drive down the road at 50 mph and the car feels like its driving over stones in the road its vidrating off the cv joint then when you turn the wheel on full lock to pull away you here a very big cracking or clicking sound, like,,,,,click click click, and the more power you put on the more they click very soon people start turning around and look at you? oh yes they here it to!
the vibration that comes off the cv will reck the transmission becouse of the wipping of the drive shafts,,,, to test your cv joints to see if there good or bad one's put the car on full lock and pull away,, if there is a cracking sound or a klicking sound there shot away and you need new ones fitted
now then,,,storie over,,, its time for sleepy sleeps

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SOURCE: CV joint questions

A c/v joint is pretty much just a better universal joint in that it permits more flex range than a simple cross. (like a driveshaft universal) If it were possible to make a universal with eight caps instead of four, it would have similar range but would be impossible to install.
Few suv's used in street applications have a true locking front differential as that makes steering very difficult on turns (outer wheel needs to turn faster than one on inside of turn as the outside "circle" is larger.) Most suv's have an "open" differential that permits easy turning. In reality most 4x4's only have two wheels driving the vehicle at any one time. Most optional setups have a positraction diff ( also known as a limited slip as it allows for slippage so wheels can change speed on turns)at the rear giving you a total of three wheels pushing. Off-road guys will often install a posi at the front, or a more radical approach is a "spool" that is 100% locked all the time, making street driving nearly impossible. Your front differential is "locked" or actually connected to the drivetrain by way of a transfer case that does exactly that...It transfers power to the differentials. On some it does this automatically by way of a viscous coupler inside the unit, or others that are engaged by the driver by either an electric servo or a direct lever.
How far you turn the front wheels determines how much stress you are putting on the c/v joint. Most vehicles have a "stop" bolt somewhere on the suspension that stops the front end from turning further than it should. Most times the steering pump will begin to whine as you near the limit.
C/v joints should last a very long time. Generally they fail because though they are internally designed very well, they are protected by a simple rubber boot. Once that boot is torn, split or otherwise compromised, road dirt enters and quickly destroys the joint.
Once you find a split boot you can almost bet that the joint is in one stage or another of failure. The price of the boot is often about one third the price of a complete joint or even a replacement axle with joints installed. therefore changing just the boot is foolish.
Symptoms of a bad joint are clicking binding or vibration from the area of the joint, but, sometimes vibration can be caused by wheel balance or a failed hub bearing. Making good diagnosis important.