Dating old bikes
Dia-Compe cantilever brakes don't appear to have a date code, but supposedly the 981, 983, 986 brakes were first introduced in 1981, 1983, 1986, etc.Following Ben's lead - I checked three sets of Dia-Compe G calipers and all have the four-digit date code on the back of one of the arms.Especially useful, and challenging to sort out and verify, was the Shimano code.Also gathered on this page are date codes decoded and generously provided by others.The rear derailleur freewheel/cassette and chainwheels are probably the first to be changed on a bike.On a vintage bike in excellent condition (that apparently had a lonely existence in a garage) all of the components likely are original.
Fueled by this first realization, and with the help of other bike folks, Larry and I have sorted out other codes (a project still ongoing).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.)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.
Swaps also can be made as the bike falls out of favor, or is being sold, where the higher quality components are traded for lower quality ones that the owner had onhand.