The STS may be superior in most crops but, you can't beat the longevity of a pre- '99 JD combine compared to the '99 and newer models. I'd be willing to bet there just as many, if not more 9x10 vintage combines in the hands of original owners than there are '99 and 2000 model JD combines.
I owned a 97 cts which was traded on a 01 9650 sts. And now I have a 9660 sts.
We harvest in fairly tough conditions mostly and found that the sts was quite a bit faster combine. I know it is a superior combine in canola and slightly better in barley and wheat. Peas you have to change the concaves otherwise to many bounce out the back end. You will find setting the sts very simple as generally you can go by the recomended settings from the manual. I usually only speed the fan up above the factory settings and the slighly opened the seives as well. Biggest, most important adjustment if things aren't seperating well is to push the hydro lever ahead a little bit more and then the rotor fills up and starts to seperate better. Biggest problem most old john deere operators have is overcoming the urge to pull back on the stick. Sts's need a full rotor to operate best.
How many hours are on your 03 sts?
There seems to be a plethora of aftermarket upgrades now for the sts's. Many of which i'm just waiting to put in when the OEM components wear out.
I never change concaves. Harvest peas, lentils, wheat, durum,, flax, mustard with the same set. Only thing I do is throw a set of filler plates in the middle concave when doing smaller grains and pull them out when doing peas. Seems to work very well for us. I also agree with keeping an STS full at all times.
I think you can chip the 9650 without causing toooo many problems. A techy told me that the 9750 has a little heavier main seperator engagement clutch. But other then that the 96 and the 97 were essentialy the same other then the hopper extension's standard on a 97.
At 1400 hrs I would start measuring all the wear points and then replacing the worn items. I would do this myself. I just don't trust the "greenlights" that sales departments do. The operators manual is very detailed on all the procedures. Both what to measure and how to do it. If you have to replace the rasp bars. I realll like Kuchars idea on how they do the "bullet rotor rasp bars".
Which concaves do you run, the small wire or the large wire? What % splits do you usually see in your peas?
I run the large wire concaves and tend to see 5-6% splits if the straw is too tough, like in early morning or late evening and .5-1% splits when the straw starts to dry out. I have tried running the large wire for everything, but even using cover plates under the concaves, I could not get the whitecaps out of the wheat.