Meaning
It was common for musicians to jump onto freight trains to visit nearby towns and farms. Later they moved on to other states and metropolitan areas. If the crew didn't allow the bluesmen a free ride, they sought other ways to travel for free. As an empty wagon or "riding the blind end of a railcar."
An other, but uncomfortable and dangerous, way of a "free ride" was "Riding the axles". They placed a board on the axles of a wagon and lay under a wagon.

In Jimmy Burns Red Hot Woman:
Pretty little thing, can't you see
What you doin' is killing poor me
Stop it baby, stop your fussing around
'cause if you don't stop it mama, have to shut your damper down

Sound clip Greyhound Blues Band

Meaning
The damper (slider) on an oil heater and wood stove regulates the heat. A person is compared with a heater, which radiates heat too much . By closing the damper the stove goes off.

Compared with Turn your lamp down low.
For instance in; I want just a little bit
turn your lamp down low and honey slip my kiss...
I don't want much, just an ini wini bit of your love

Also is used; Turn your damper down

YouTube clip; Magic Sam (in the original song of Rosco Gordon)