I'm a newbie and recently took to commuting with a ten year old bicycle. I wiped out on my first ride home from work. During the wipeout, the brake levers mounted on my handlebars became loose. I cannot for the life of me figure out how to tighten these Shimano levers on my handlebars; there's no apparent screw to tighten. What is this moron missing? How do I tighten these things? Thanks in advance for your help.