My recommendation is to go talk with your most trusted combine John Deere mechanic and ask him what to look for and then see if they could go look at it.
I just bought a used 9660STS eventhough I talked with the mechanic who always does my combine inspection, I didn't ask him to go look at it. And now we've found somethings I never thought to look for. The 60 series has a lot of little spots where cracks develop and if you didn't know to look for it, you would never see it.
Some areas I've learned to look at are the contour master feederhouse where it pivots, the backside of the contour plate, feed accelerator, primary gearcase mount, threshing elements, concave wear, discharge beater wear strips, chopper knives, look for cracks around the chopper and tailboard.
This is only a short list, there is much more to look for.
My 2 cents. Fortunately, I've gotten look so far, only $5K spent, but probably another 4-5 to go.
Would alos recommending comparing the price on a new head vs. a used one. The header that came with my 2004 9660, they wanted $24K, but I ordered a new 630F for $29,600.
From my experience of selling both 9860's and 9760's yes, they will need the same amount of repairs. The big differences will be fuel consumption being more with the 9860 due to engine size and resale value in my area seems to be about the same on both machines (and in some cases, the 9760 is more desirable).
Obviously you guys have never seen a 9860 Premium. I think we only get those in Canada. One of my customers brought a plain 9860 up from Kansas and it was hardly any bigger than his 9750. Premuim has 425hp, high capacity feed package, stronger concave adjusting assembly and a bunch of other stuff that makes it work well in our tough conditions.
The 9860 premium came out in '06 (I think, someone correct me if that's not right) and was made available in Canada and it seems like Deere dealerships in the Reno Branch also sold the premium, if I remember correctly.
kscombiner, you hit the nail on the head. Good machines are good machines, and it can't be stressed enough that dealer support is vital.
The limiting factor on a 9760 is usually the sieves very rarely the engine power, if ur doin wheat i would definetly invest in 36 foot draper header, JD's is well built and solid belts are expensive but if u can figure out a better way to join them u'll get more out of them
there are few major things you are going to want to check on that combine. you need to check all the augers and make sure they aren't getting sharp if so decide wether or not they are shot. if you think they will run another year or two go ahead and pull all of them out and tungsten them. it will make them last for another 6 years. you also need to check the top covers on the rotor make sure they are not getting thin or have any holes. make sure your feeder house floor doesn't have any holes in it. If it does go to your local iron shop and have them make a floor out of AR plate. it is about a third of the price as one from JD and lasts alot longer. i think that is most of the major things. if i think of anything else i will let you know.