Gosh, this is my favorite subject. I always feel obligated to comment.

According to many here, simply owning a cone type sure grip may be the worst thing you could do in life. Any of you nay sayers care to tell me how or why this thing works (which is the same principal as the clutch of course)?

I never had trouble myself, but from what I hear here, my car has no value because of it (I might add my splines don't line up on my steering shaft either).

You can grind some off the cones as stated, and if you wish, get the pre-load back by adding a big diameter washer in there about the thickness you take off.

If you are worried about the metal, put a magnet on the housing somewhere at the bottom. Chrysler never worried about it and they warranted them for 50K miles. I have never seen an excess of metal in the oil even after one of these was wore out. Must go somewhere though.

This unit also has much bigger sypder gears than the clutch type, which are prone to breakage in the clutch type, but nobody ever mentions that.

Have fun, don't believe every thing you hear here.

All that metal in the oil is not a myth ... the cones are wearing out because they are grinding away EVERY time the car turns ... spiders will weld themselves to the spider pinion when the cones bottom and you keep doing burnouts, it can even happen to a peg leg after 2 many one wheel burnouts.

Get out the waders it's getting deep in here ...

You need to add MORE than the amount you take off the cones , if the cones are already bottomed out then the spiders already have increased backlash.

All that metal in the oil is not a myth ... the cones are wearing out because they are grinding away EVERY time the car turns ... spiders will weld themselves to the spider pinion when the cones bottom and you keep doing burnouts, it can even happen to a peg leg after 2 many one wheel burnouts.

If one hasn't seen the damage they are either Helen Keller blind or inspecting the parts from across a dimly lit football stadium. ...just look at the gear teeth, and the bearing rollers and races with a magnifying glass to see all the little pits.

1971 Sport Fury 440" 727 with an 8 3/4", 489 housing and 2.76 gears, the tag is still on. It locks up on dirt and snow but not on asphalt so it needs rebuilt.
From what I've heard all Sure Grip's from 1969 are cones, it this correct?
Is it possible to rebuild a cone style differential, and if so where do I find the parts?

Now, with this established, we should know the principal behind how it works, any one care to share?

Pretty simple. The spider/side gears are cut fat at the base, and narrow at the top. This means that they WANT to separate, Spider gear from side gear as torque is applied. More torque, more side force.

This side force is transferred to the cones, which attempt to wedge themselves against the case. When this occurs, you have lockup and each axle will spin the same RPM.

If there is not enough force (including when the cones eventually bottom out in the case) the differential will, well, differentiate---good for corners, not so good for acceleration.