The "servo" term refers to how the gears are shifted, the actual power transmission is a conventional gear train. The speed dial moves a spool valve which controls pistons which actuate the otherwise conventional shift forks.

A pump circulates the headstock gear oil to power the system. The shaft on the other end of the pump motor moves an eccentric link that the spindle brake is attached to that "jogs" the gear train until the gears engage. Must be an all-time great Rube Goldberg hack.

The above photo shows the headstock open and empty. The aluminum casting across the top is the shift servo mechanism.

In the above close-up you can see one of the shift pistons, it's the shiny shaft in the middle of the photo, that emerges from the casting on the left and actuates the orange-painted shift fork on the right.

Relay logic in the electrical cabinet controls the shifting. The lathe shifts gears when the brake is engaged after changing the speed dial. A sensor waits for the spindle to stop before turning on the shift pump.

Click to see photos of moving the lathe