What kind of brush are you using? you should do the arm test to see how harsh your brush is. also i agree with the above poster.. to dampen the hair so it doesn't break.. remember yorkies have hair not fur! i've heard that a good brush for these types of dogs are brushes with no pins on the ends, but not the slicker brush (this is for the body) and the arms/legs/feet you can use the slicker brush..
I personally LOVE Chris Christensen's products...
http://www.chrissystems.com/tiptest.htm
Why Proper Brushing is So Important.
Other than the primary function of brushing or styling hair, hair brushing serves several other important purposes; cleaning and massaging the skin, and stimulating the release of a beneficial oil called sebum. Sebum is released by the sebaceous gland at the base of the hair follicle as a result of the gentle hair tugging action caused by brushing. Brushing the hair cleans the hair shaft, follicle, and skin by removing trapped scale, dirt, and oils. Brushing also distributes the Sebum, coating, lubricating, and protecting the hair shaft resulting in a healthy glow or sheen and more flexible hair. Because sebum protects and moisturizes, regular brushing results in hair that is healthier, more manageable, and easier to style. All of Chris Christensen Systems brushes are well balanced and easy to use. Handles are designed to ensure comfortable grip and use.
You May be losing More Coat Than You Realize.
Thick, full coat means a healthy coat. When the coat is thick and full, it's usually healthy, shiny, full of volume and body...most everything you want in a great-looking coat. By using the right tools you can reduce excess coat loss (including thinning, breakage and splitting).
Much excess coat loss CAN be prevented.
Coat loss has three causes. 1. medical conditions, 2. genetic & hereditary factors and 3. physical or chemical damage to the coat from bleaching products, blow dryers and inferior grooming tools and all around improper styling techniques. While some coat loss cannot be solved, the majority of excess coat loss caused by breakage can be prevented by treating the coat right and using proper products and tools.