Okay from what i can make out i think you need to losen one of the collets with the approaiate allen wrench. ThIS allows the brakes to be ajusted Depending on how hard you push it aganist the fuel tubing.The piece of white silicone that is missing is allows pressure to be applied on the brake causing it to come to a halt. a piece of fuel tubing can be used for this. If you want me to post a picture let me know. I hope i got it right

Regards

Gary McD