57 chevy truck shifter problem

[57chevyman]

hey y'all.. I have a problem with the truck.. maybe someone can give me advice so I can fix it myself -

I have a Saginaw manual three speed transmission in my truck. shifter on the floor. I seem to have a problem with the linkage - if I shift it into reverse ( top, left ), I cannot shift it out of reverse. the last 2 times I did use reverse, I had to either drive home in reverse like sonny from Bronx Tale, or get under the truck and get it out of reverse ( on a flat surface and wheels blocked!)

I can post pictures tomorrow if that helps.