I think I would just forget about using a slicker brush on his coat type. I don't think it's the right brush for him. Instead I would get yourself a Zoom Groom. You can get them at Walmart or in any petstore usually. They are made by Kong.
This is a great brush for both of your dog's coat types. You press the rubber knobs into the dogs coat and rub it in vigorous circles.

Here's a pic of one.

http://www.kongcompany.com/grooming.html