Helpneeded with manuel Shifter 1966 c 10

[Mike c 10]

hello
Hope you can help me ..Ive a 1966 c 10 with manuel Transmission . the shifter sits on the steering colum . When I drive sometimes I can manage the gears only the first vgear will goo or only the second .or only rear .. I think the part that sits on the steering colum in front of the Firewall didnt work so god. I dont know what the Name of the part Maybe someone can help me or have one of those parts... Many thanks !!!