Try something like this for the undercoat and a long bristled slicker like this and a greyhound comb to check your work. Look up how to line brush as well

It's not a rake but it's one of my favorite brushes and it will work well. You can still go over him with the rake after but I would use this first.

Paw Brothers Slicker Dog and Cat Grooming Brush for Professional Pet Groomers - Easy To Use - Comfortable - Removes Long and Loose Hair https://www.amazon.com/dp/B014PFS2VE/ref=cm_sw_r_apan_glt_fabc_33RQJZ48AN3ZKF5A0HE6