The AM station adopted a highly popular Top 40 format in the 1960s and became the flagship of the (now-defunct) Radiomutuel network in 1969.

CJMS, along with other Radiomutuel stations, switched to a news/talk format in the early 1980s, which resulted in Quebec having two separate popular AM news/talk networks covering most of the province (the other one being Telemedia, whose flagship was competitor CKAC).

For various reasons, including the prolonged economic recession, the licensing of Télévision Quatre Saisons (TQS) in 1986 which persisted in their practice of selling advertising for extremely low fees, the presence of a third French-language news/talk station in Montreal (CKVL) and a general migration of listeners from AM to FM, both networks had less-than-stellar financial performances.

Telemedia and Radiomutuel secretly decided to merge their operations to form the Radiomédia network in June 1994.

[1] The merger deal was publicly announced on Friday, September 30, 1994 at 9:15 AM, and in each of the six markets where the two networks competed, programming on the station slated to be closed immediately stopped and was replaced with continuous music fed directly at the transmitter site.