I have replaced the track adjuster on my 4350B with no problem. I am now helping a friend with his John Deere 450C. The piston is so securely rusted into the cylinder that it cannot be separated (we tried heat, jacks, penetrating oil, etc.). We have the track separated, adjuster unbolted from the idler, and idler slid forward. We tried to remove the piston/cylinder as a unit, but the piston end will not release from the retaining cap in the spring. It rotates freely and can be moved back and forth about 1/16 inch, but cannot be pulled out of the cap. It feels like there is some solid metal preventing the piston from sliding out, but the manual does not show anything being there. I thought there might be a need to rotate the piston to remove it, but it cannot be rotated with the cylinder attached, as the ears on the cylinder interfere with the track frame. I suggested cutting the piston, but my friend thinks he would like to try and rebuild the unit, since he already has the seals. As a last resort we might just keep this rusted unit in place and adjust the track by adding shims. I did this for awhile with my 450B and it worked fine, but he wants to be able to adjust it with the adjuster. Any ideas as to what is preventing removal of the piston from the spring cap?
Rust.
If it is rusted to that point it will be futile to reseal it. Those are all over the internet in aftermarket and reasonably PRICED.
Scrap it and replace it, I'll pile on if it's that far gone it needs to go. It should slide out of the spring cup easily and with a little convincing out of the idler fork too. I just had a 550A apart with no issues like you are describing.
I thought it would slide out of the spring cup, as it did on my 450B, but it feels like there is something solid (hard) holding it in there. We tried pulling, jacking, and even hammering on the back of the front fork with a sledge, but it won't budge. It feels like there's a solid metal "keeper" in the cup, but no way to access it, and can't see in there because of the spring.
Jdparts.com should clear up any doubts you are having, it sounds like you need a BFH and some more persuasion to break it loose, you could try pulling the sprocket off and pushing from behind it too, worse case scenario, you could torch the spring and replace everything?