@kgdjpubs posted:Jack can probably answer this better. There was a whole bunch of experimental stuff built into the A-1, and the T&P 600s came right after that. I’ve heard several reasons why, but the main frame ends at the back driver. The firebox is supported over top of the trailing truck and the drawbar attaches directly to the back of the trailing truck. It’s a bit of a Frankenstein design that caused no shortage of problems and Lima moved away from it quickly. A few of the 600s were upgraded to a new full frame, delta trailing truck and roller bearings towards the end, but none were saved. It improved the engine but not enough to starve off dieselization.
My understanding was that the trouble with the articulated trailer was that they tended to derail when backing up with any appreciable load in back of the tender. Apparently they were fine when pulling in a forward direction.
Fortunately, backing movements tended to happen during low speed switching. I don't recall reading about any major catastrophic wrecks being caused by the articulated trailing trucks.
