Didderential experts-Explain"roll pin"4X4 article

[PHOEBISIS]

I know we have some differential experts-knowledgable amateurs out there-maybe one-some of you would explain the differential failure that the 4x4 mag experienced.Make it detailed,but simple.I saw the picture,and it looks like the sheared pin was holding another pin in place.It isn't clear what sheared the sheared roll pin(I see a scooped out place that is scooped out to allow the pin to be driven in,but I don't see anything that would shear it off),and since the sheared roll pin didn't drop out,it isn't clear to me why it isn't still holding the "other pin-carrier pin".Did the sheared pin back out enough that it no longer is holding the 'carrier pin"??
Maybe you could start with some quick definitions-assume we know nothing about differentials other than they transmit power,and allow the outside wheel to not drag.Define pinion-ring-spider and trace the power transfer from the axle through these gears-like this-axle> etc.Thanks.Show us what sheared the roll pin,and what a loose "carrier pin" would hurt.
Would excess heat make the pin more likely to "back out"-make the hole it is driven into "expand"?This is about the only hard fact we have about a diff failure-hence the curiosity.
Big order-thanks.Charlie

[bestatchess]

http://www.broncograveyard.com/dia/6/d44diaaxle.jpg

I think the pin that sheared is near the Ring Gear and Open Carrier in that exploded view. It holds the cross shaft (pin) to the carrier. This might support the theory that ABLS causes the failure by heavy load on the spider gears.

[PHOEBISIS]

Best,thanks.A question or 2.
1)ABLS is on all 4x4?
2)How active is ABLS when someone is just driving down a dry road in 2wd?Wet road 2wd?
3)Is there some signal that tells the driver that it has been activated?I curious to know if members could give us some idea on how often it "kicks in".
Thanks.Charlie- 14 of 16 have been 4x4's.

[bestatchess]

cutesy little animation:

http://auto.howstuffworks.com/differential3.htm

cross shaft & spider gears shown in red

In the "inner wheel slower" picture, visualize clamping the slower axle against movement by applying the brakes to the rotor on that side. This will transmit all of the drive force to the other axle through the spider gears. The force exerted on the spider gears will in turn transmit a component of the force along the axis of the cross shaft (perpendicular to the roll pin), which apparently is too much for the roll pin to handle.