Joey's breeder is a show breeder and is use to working with long coats, she swears by the shampoo called Biogroom and says that it was specially formulated for Yorkie coats. I've tried other shampoos, because I'm kind of a shampoo nut, but I do think it the best shampoo and conditioner I've tried. You can get a free sample of their products by requesting a trial pack; their products are very concentrated, and you should mix with 4 parts of water for one part of product, so their little sample bottles go a long way. Just click on "contact us" and request some samples.
Bio-Groom - Exceptional Pet Care Products for Over 30 Years