Throughout their NZR careers, the AB class were known for their Vanderbilt tenders - one of three classes to use this tender, the others being the re-built G class 4-6-2, and the later J/Ja/Jb class 4-8-2 engines. The tenders, although satisfactory, suffered from having been constructed too lightly for the intended task, and were also prone to rusting, particularly around the frame channels. This necessitated the complete replacement of the tender frames from some locomotives, although not all were treated so.