Weinmann and Dia-Compe calipers usually have codes on the back of a caliper arm.
This can be simple like "0784" (month 07, 1984) or a clock-type, with year in the middle and a ring of numbers with a tickmark pointing to the month.""Dia-Compe road levers usually have a code stamped _inside_ the lever.
As the wear on a vintage bike increases, the greater the likelihood components are not original, either through replacement of worn parts or through component swaps.Swaps can take place early in the life of a bike as the proud new owner upgrades to new or used components of higher quality.The Appendix gives dates of initial manufacture for the vast majority of derailleurs made from 1920 to 1999.Other manufacturers of bicycle components have date marks on their pieces.This clearly is when the component was made and not when the bike was made, but unless the component or bike manufacturer had lots of stock lying around in inventory, the date should be a fairly good indication of the year of the bike.
At least it would be the earliest date that the bike could have been made.Unfortunately, many of these are coded, and require some additional knowledge to understand the code.If you know of other components that are marked or coded that can be added to this list, please let me know.: The information on this page is copyrighted.)Most early Treks (1976 through about 1980) were sold as framesets.The components were added by the local bike shop or by the buyer. Components also could be swapped from an existing ride to the new frameset.Especially useful, and challenging to sort out and verify, was the Shimano code.