If I understand you correctly, you have a Delta 20CU, a "clutch drive" control. These controls do not use servo drives to position axes; they use one, single speed motor that is "clutched" to the X or Y axis to drive the one that is commanded. Speed is controlled through a transmission with shifters that need to be moved to get the desired speed. The CNC control kept track of commanded position and how far away from that position the axis is. As the axis approaches the commanded end point, flags or "switch" points are turned off. As each successive switch point switches off, the axis slows until, once all points are off, the axes stops.
The distance for the final switch point is set in the Setup mode (mode 5). The other switch points are set in the parameters, which is non-volatile memory (an EPROM).
The prints for the Lucas machine always had a chart showing the shifter positions and associated solenoids and relays that corresponded to axis speeds.
I think you have one or more faulty relays or solenoids. Changing the ladder is impractical and, I think, unnecessary, if you can find the faulty relays and/or solenoids.