Here's some pics of the transmission brake assembly. It's a bit greasy, but it should give you the general idea of how the handle hooks up. I didn't have any degreaser with me, but I will get back out this week and clean it up better for you so you can see a bit more detail. I didn't realize the handle area was this greasy. Anyway, the second picture is the pivot point of the handle, and the third pic is where the handle hooks into the part that compresses the shoes against the output shaft. I will degrease that area so you can see how the teeth hold the handle in place when pulled. More than likely you are missing a spring a something like that.

http://i21.photobucket.com/albums/b254/Bear43/1963%20C20/TransBrake1.jpg
http://i21.photobucket.com/albums/b254/Bear43/1963%20C20/TransBrake2.jpg
http://i21.photobucket.com/albums/b254/Bear43/1963%20C20/TransBrake3.jpg
http://i21.photobucket.com/albums/b254/Bear43/1963%20C20/TransBrake4.jpg
http://i21.photobucket.com/albums/b254/Bear43/1963%20C20/TransBrake5.jpg

1963 Chevy C20 Longbed Stepside
1978 Chevy K30 Custom Deluxe