Here's the latest on this ongoing saga. I called Hydro-Gear and got a real good guy on the phone (I wish all customer service people were as good as him). The first two letters on the model # were ZH and he said it was the ZT 2800 -- like you said. He said in order to test the internal I should push the bypass arm (the horizontal flat plate) forward or backward with my thumb and see if you felt a spring resistance. I jacked the machine up, took the wheel off. The bypass rod was sliding the bypass arm back and forth just as I'd always seen. So I tried what he said and I was able to move that bypass arm forward a little bit with my thumb. It wasn't much, but I could tell with repeated pushing and letting it go there was a spring resistance tension. Then, pushing the bypass arm to the rear it of course effortlessly slides to one point. From that point I could push it with my thumb and feel the spring resistance a little more so than when I pushed it forward with my thumb. Either way it seemed to me the spring tension he mentioned was there. I told him I tried rotating the axle with the bypass arm pushed forward as far as i could with my thumb but still couldn't rotate the axle freely. He said there would be some tension there because there was 5 pistons in there with some of them having pressure on them all the time, but that he wheels would roll. Bottom line: He said since I could feel the spring tension that told him the internal was working as it should. He thinks its an issue with the "linkage" as he called it. I said by linkage do you mean the bypass rod and he said yes, for some reason the control arm is not being pushed as far as it should. I don't know, thats probably true.
I think I need to say this: With the rods pulled back the rods just lay in the slot loosely. They don't look to be "locked in".....just laying there. With the rods pushed forward there is that small washer-looking retainer that you push through the hole and drop the rod down in the slot. I also checked to see if the rods would go any further once I pushed them in. They did. I felt it lunge a little with an added push. The same when I pulled them back, once I met a resistance I pulled some more and it would move some more. I'm thinking (rightly or wrongly) maybe these rods have been bent so much with sticks in the yard that they aren't functioning as they should. I have lots of trees and sticks in the yard. Those rods have some bent places on them I'm pretty sure came from the factory like that - but maybe not all of it. They are not a "straight" rod. I think tomorrow I'll take those rods off both sides and see if they are uniform. If so, and they are identical then they're not out of shape. I think I may find some variation though. If so I'll bend them like you suggested, thereby lengthening them a little. If nothing else just buy some new ones and put them on. They can't be but a few bucks.