If your truck is "original", it does not have a solenoid since you have a foot operated system. The rotation of the commutator slings the starter drive gear backward to engage the flywheel.
I have seen the starter drive get dirty and dry to the point that they will not engage, but more than likely you just need to replace the starter drive. It is mounted of the rear end of the starter commutator.
The starter does not have to be totally disassembled to replace it. Just remove the rear part having the holes for the mounting bolts.
meansam
