My 57 f100 restoration has hit a snag. Installed new speedo cable with new driven gear. Made a test run and speedo did not work. Pulled cable from transmission and the driven gear was gone. removed the tail shaft housing and the gear was in bottom of the housing. There is no backup for the gear to ride against inside the housing. Has anyone run into this problem? This is a heavy duty three speed trans. Any help will be greatly apreciated. Thanks Jim