Ok the dilemma is solved!
First I got an excellant PM that I will quote here, if the sender wants to be known, I'll gladly credit them:
</font><font color="blue" class="small">( Seat, everyone has had fun with this one !
You have the yellow slide lever for front to back on the left
next is the small knob in question, When yours was working, if you had gotten in the seat and bounced up and down as you turned it, you would find that the seat travel (up & down)
changed This took a little playing, because every one either gets off to play with it, or just sits still and turns it!
The large yellow crank does your weight preload for the seat.
The bad news is, that other than the knobs, the suspension is serviced as a unit. The shaft of the knob hooks to a spring up inside. I'm sure that either the spring broke, or just came off.
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The answer is: Plastic knob is threaded, the shaft is drawn into it under tension from the spring. It adjusts pretty easily if you are ON the seat, MUCH harder if empty. And plastic doesn't like all the tension. So the plastic threads gave out. SO:
Adjust seat vertical travel while IN the operator seat.
If yours strips, get the knob kit. (YOU look it up on jdparts.deere.com, you need the practice, its fun...) You are likely to damage the black cap, but one comes with the kit. Remove the enclosed nut, and the yellow knob. While IN the seat, screw on new knob, and then nut till it is flush on the shaft, pop in black cap, and yer done!
And ALWAYS sit on the seat as you adjust it
Bet there's a running change on this design...
Thanks for the spiffy answer!