gears on Athearn DD40

[bngreen]

I just bought an old (white/orange box!) Athearn DD40 dummy at a train show, thinking that I could put power in it using my collection of Athearn parts.  Much to my surprise, I slipped the 23 tooth idler gears into the gear box and found that they don't mesh with the axle gears...they're way too small in diameter.  Either that, or the axle gears are too small...I'm not sure which.  There's also a 45 tooth idler gear required as well, but I don't currently have any to see if that meshes with the axle gears.  The part numbers listed for these gears on the original parts sheet are the same as those offered on the current Athearn parts website (#40030 and #40031).  Has anyone had this experience?  Did Athearn change the size of their 23T and 45T gears years ago?  Thx.