I've not tried this, but Classic Parts has a spring that is supposed to help with this condition:
http://www.classicparts.com/1947-51-Door-Latch-Spring/productinfo/18-575/#.UwYzyYUz0UY

I'm not aware of pictures or diagrams on this parts - they dont' seem to be designed for servicing. Last time mine needed work, I took it apart and used an old one for reference.

Good luck & have fun working on your truck.

Bill


1947 3100 Advanced Design

Never, never, never, never give up. - Churchill