They had a habit of bottoming out quite alot some years back, indeed on one ocasion I closed the UP Fast behind us for a suspected broken rail/pulled joint in S&C because of the bang.
As for lively rides, sadly the experience of an 81 to 85, especially 83s/84s can never be repeated but believe me it was quite something, rocking and rolling like a ship in a storm at 75 with a car train behind was the favourite experience of mine.
In those days we judged how bad a track fault was by whether or not the Driver had been thrown out of the seat. If he had it was a block the line job, if not it was a caution job !