Here is a video of the HD axle kit apart it should help and I think you have to shorten the cable so it is engaging and there are several adjusting bolts around the brake as well. Adjust each one until you feel some resistance and the back it off slightly but your cables need to be adjusted just right . And the V brakes need to be adjusted just right as well if not you will not get real stopping power. Clean the brakes and rims with alcohol.
YouTube - Felt Twin BILLY GOAT GREEN Grubee HD Axle Kit