By Oletimer
United States 
My hundred year old pear tree, in the last 4 or 5 years has begun to stop providing many pears. Most of them dry up and fall from the tree when no larger than the size of grapes. Some fall at this size then dry up while others dry up on the tree, and then fall. It used to be covered with hundreds of some of the sweetest small pears but not any more. Any suggestion? Like I said it is over one hundred years old and to my knowledge, nothing has changed to negatively affect it. Thanks, oletimer
5 Jun, 2018
Well I'm sorry to say that its likely to do with the tree's age - the lifespan (and certainly productive lifespan) of a wild pear tree is up to 50 years, more or less; modern, cultivated variants have an even shorter life span, see link below. I think your tree has more than served you well down the years by the sound of it, but sadly, all things must pass...
https://www.gardeningknowhow.com/edible/fruits/pear/pear-tree-lifespan.htm
5 Jun, 2018