I have heard that the spoke nipples can pull through the rim fairly easy.
Here is a quote from Sheldon himself:
"
Older Treks generally had very nice frames, well worth keeping/updating. The one area of weakness was that they tended to cheap out on the wheels. Many of them had the horrible Maillard Helicomatic rear hubs, and Trek house-brand "Matrix" rims. If you want a nice rider, an old Trek frame with new wheels can be a very nice classic ride."
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