Do I have to remove the transmission pan to install a new detent cable on my 86 Camaro

 

It's not necessary to remove the pan. The end of the cable at the trans end hooks into an eyelet coming out from the trans. It's a little tricky getting the new cable hooked into the eyelet, but with a litte patience you'll get it hooked up eventually. There's one 10mm bolt that holds the cable in the trans. Undo that bolt and you can lift the cable assembly far enough out of the trans to disconnect it from the eyelet.