My prop will not engage when shifted to Reverse. There is no movement on the lower shift cable when I put the control in the Reverse position. However, I was able to shift by just pulling on the lower shift cables manually. The lower shift cable has been replaced a couple days ago by a local marine mechanic when he did the U joint, seal, bellows and impeller. It also makes a humming noise in the outdrive when shifted in gear. Gimbal has been replaced too. I am trying to see if I can adjust or replace the control & throttle cable or do I have to replace the whole control box? Where can I buy the cable for the control & throttle? I do not want to have to replace the whole control box. Thank you in advance for your advice.