Turnbuckles Underneath Old Cars

Can anyone tell me what the turnbuckles were for underneath old passenger equipment? What did they connect? What were they used to control?

My best guess would be that they were used to take up the sag as the wooden and early steel or iron frames of the cars aged and weakened. I've seen decrepid old coaches that were sagging to the point where they were almost scraping the rails (out of service of course). As steel technology and the strength of the frames improved, the rods and turnbuckles were no longer needed.

The turnbuckles were part of what were called "truss rods". The truss rods were connected to the end beams of the cars and were threaded under what were called "queen posts". Tension on the truss rods was transferred to the queen posts as a vertical force to the car bottom, keeping the car from sagging. The turnbuckles were used to compensate for stretching of the truss rods so as to maintain the correct amount of tension.

If you've heard the expression "riding the rods" that's where it came from. Hoboes would sometimes ride on the truss rods, either by hanging onto them directly or by placing a plank across them to lie on. Must have been a wild ride, watching those ties and rails speed by right below you.