D6 9U New to me

There are options to Cat sources. Undercarriage parts are still plentiful as aftermarket items. Key is to track down part numbers and inquire as to where the items can be obtained. Current track and sprocket solution is to go the 6.91 inch pitch to replace the old 6.75 inch version.

Replace the whole thing then. can the pads be saved and used on new rails? I was hoping to get by with rebuilding the idler and replacing the sprocket 😊
The CAT service guy lives about a mile from here, once the machine is in my driveway I may flag him down to talk about it....

I ordered parts and service manuals a few minutes ago.

Before you make a decision price new track rollers and sprockets to match your rails (get part numbers off them and or measure stretched lengthof 4 links center to center of 5 pins)

If it still has 6.75" rails but they are worn to 100%+ (and it sounds like they are since the adjustment is all the way out), you might be able to swap to the 6.91 bolt on sprocket segment type weld-on ring. If a new 6.75" pitch ring doesn't result in enough improvement to the track tensioners travel, you can consider having the pins and bushings turned or if that is not justified, or you have a 6.91 ring installed, a link can be cut out of each track and return the adjusters to the fully retracted position.

One thing to watch out for if you need to back the adjuster in all the way, the threads which have been exposed for years while the tracks were too long will be rusted away and may soon strip if the tractor is operated when the bad threads are screwed back into the nut. Better to replace the adjuster bar before this happens than to ruin the "nut" too. Last one I bought was from Florin and was quite reasonably priced, maybe $100-ish.

If your final drives are leaking oil down the inside of the sprockets you may want to have the sprocket rims replaced after pulling them to fix the seals. If the seals are good, the rims can be replaced with the sprockets still mounted on the tractor. If only the outer seals are leaking, those can be replaced when the track frame outer support is disassembled to install the ring.

Lots of options depending on what you find.

Oh........we like pictures!

Good information. Thank you both! I will be measuring the rails this week once it gets moved here.

I would also give consideration to looking for a parts tractor with a bad engine and good or average undercarriage.

So I finally got it home last night. The undercarriage is toast. The rails are 100% worn. The bushings weren't which tells me that someone replaced them at some point when the tracks were getting pretty worn but they didn't address the rest of the machine. One upper roller has a broken flange. There are no grease buttons on the lower rollers and the previous owner had said they were sealed. I paid $4k for it, so compared to what I have seen in the Northeast I don't feel so bad. Granted I would rather not need to replace the undercarriage but it is what it is. Both pony and diesel run well.

I can look for donor machine but I think I will start down the route of replacement.

I suspect it makes sense to follow Old Magnets suggestion to go to the 6.91 pitch.
Searching through the forum and trying to put it all together it looks like replacement looks like:

New sealed upper rollers ( i'm willing to bet that the rest are worn out but i'll check more carefully)
New sprockets and rails - from which model? D5 or D6 and does year matter? I have spoked rims, do they get cut and welded or will do new ones get pressed on?
Possibly new bottom rollers - again, off what machine. I can't really tell how work they are. I need to do more research...
Will my track pads bolt right on to new rails?

Thanks in advance!

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With new undercarriage, it will be an enviable machine. Folks on here have good examples of the Cat canopy if you need measurements to re-establish it.