I'm no longer certain about this.  Steve Gerstner seems to feel very strongly that a d80 is stronger despite the 14-bolt's extra bearing due to the contact angles of the gears and the support bearing spacing.  He has built several 80's to replace broken 14-bolts in his customers' mud trucks.  He said he had one who busted seven 14-bolt gearsets in a row and went to an 80 to solve it.  I'm not a differential engineer so I have to put faith in what those who claim to be say.  He claims that the 80 is the first computer-designed gearset and much stronger as a result.  The bearings in a 14-bolt are MUCH closer together than an 80 which makes the 80's load rating much higher and in theory the 14-bolt's shorter pinion shaft will twist less before snapping and the 80's longer shaft will twist more.  (Why people break so many more stub and short-side axle shafts than long.)  The 80 has a microscopically larger pinion shaft with more splines which makes the minor dia. larger than the 14-bolt's.  He also claims that the design of the 14-bolt was directly copied from the Ford 9".  This makes sense when you see the two pinions of equal ratios sitting next to one another.  The gear portions are very nearly identical in size and shape.  He argues that if you want a 9" pinion with a larger ring gear and a design that was done by hand back in the 50's, get a 14-bolt.  But if you want something that will hold up, has genuine mass, and was designed recently with computers get an 80.

I think both are strong enough for what we do and 14-bolts are cheap.  But I am willing to experiment with 80's personally as I do believe they are AT LEAST as strong as 14-bolts if not stronger and they don't have many more associated drawbacks.

I have a d80 5.38 gearset sitting here.  I wish I had a 5.13 or 5.38 14-bolt to compare it to ...

Finally, Chevy seems to agree with Steve because in all their higher load rated 1-tons they replaced the 14-bolt with an 80 when they easily could have just continued putting 14-bolts in them.

J. J.