I checked my pads on the rear of my 07 expedition. The top and bottom leading edges were worn on both the inner and out pads (both wheels).
The middle of the pad has most of the material left while the leading edges are almost gone.

Trying to post pics but hosting site not responding.

Any reasons why top and bottom edges are wearing like this. Is this common for rear disk brakes?

 

Do the pads look similar to this? http://www.autoextreme.co.uk/AutoSho...Blackstuff.jpg

If so, that is how they are designed. Post a pic of yours.

 

Yes that is how they look. At what point do you change the pad if the leading edge is getting thin? By thin I would say 1/8 or so.

 

I would go by the center thickness. If it is less than 1/8" or so replace. Don't forget to turn the rotors.

 

Berry Thanks for your response. I have the truck on the lift. I took one side off for complete inspection and was getting ready to do the other.
On average how many miles are the pads expected with normal driving. I have almost 40,000.

Rear seems more worn than front.

 

It all varies. Ford pads are typically softer and wear quicker. I have seen pads go in 20K and I have seen pads last over 100K. Measure your center thickness inside and out and let us know what you have.