See you have had a couple dozen hits on this post but no replies. Wonder if it could be others including myself aren't exactly sure what you mean. These models have a hydrostatic steering system. There is a valve assy attached to the steering column.
Here is something I found in an old service manual that might be of help.
Yanmar FX 24D
Yanmar RS 1300 tiller
Cub Cadet 3204
48" HD mower
Bolens 1257 w/36" tiller
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