the pin that clicks on when u put it in reverse is broke in the transmission

it sounds like the detent has failed in the valve body. it is quite a job to remove the side cover to gain acess. suggest you take it to a trans shop to confirm and get a bid. i am concerned where the broken piece went as it may cause other issues if you dont attend to it soon. try our shop locator tab at the top of the page for a shop near you. Roy