It is not too late to thin your pears, if only to keep branches from breaking down. The following information comes from an OSU extension publication and describes when and how to thin apple, Asian pears, and European pears:
"Learning how much fruit to thin off your tree will take some practice. Each fruit type will require a little different method. When working with apples, Asian pears, and European pears, thin fruit to one per spur. The spur is the short woody structure where flowers arise. You should leave only one fruit for about every six inches of branch. If your tree is healthy and vigorous it will have more than one spur every six inches along a branch. So you will need to leave some spurs with no fruit on them. This helps to balance your crop for next year. When choosing which fruit to leave look for the largest fruit. Fruit that is small or damaged should be dropped first. Homeowners should thin fruit as early as possible. Thin before each apple reaches the size of a dime in diameter. This usually occurs within the first 20 days after petal fall. Removing these small fruit early will keep energy available for the fruit that remain and fruit buds for next year. Thinning by homeowners is typically done by hand. Be careful not to break off the spurs while thinning. Spurs will produce flowers and fruit for many years if not broken during thinning and harvesting."
This information comes from http://extension.oregonstate.edu/douglas/fruit-thinning
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