On my DK 35, when I want to engage or disengage the 4 WD I push/pull on the 4 wheel drive leaver while driving, accelate hard with the foot throttle and leave off on the throttle while I have slight pressure on the 4 wheel drive lever and it easily engages into or out of 4 wheel drive every time.
No stoping, no grinding, no fuss. Works smooth and easy for me every time.