He is also famous for having developed the talents of many outstanding players, including Günter Netzer, Berti Vogts, Jupp Heynckes, Rainer Bonhof, Allan Simonsen, Uli Stielike, Bernd Schuster and Pierre Littbarski.

The club's most recent major title had been its win in the German cup in 1960, and it had found itself in the second division after the inception of the Bundesliga, finishing eighth in the year before he arrived.

At the end of the year the team was crowned champion for the first time, and twelve months later the club from the small town became the first side in Bundesliga history to defend the league title.

The team's first European Champions Cup participation had ended in the second round, when after two 1–1 draws with Everton, Borussia lost in the penalty shoot-out.

During their second challenge, Helenio Herrera's catenaccio specialists Inter Milan, at the time one of Europe's most celebrated sides, visited the Bökelberg stadium.

During the first half of the match, with Borussia leading 2–1, Inter's Roberto Boninsegna was allegedly hit in the head by a soft drink can thrown from the stands, and had been stretchered off.

The empty can was presented to the referee, and afterwards when Inter's officials complained, the governing authorities annulled the match and ordered it to be replayed on a neutral ground.

In the Bundesliga, only three days after the initial triumph against Inter, the Foals defeated the surprise team of the season, Schalke 04, 7–0, but Bayern Munich won the title and Borussia finished third.

Before the season Borussia had let Dietrich, Horst Köppel and Herbert Laumen go, and important parts of the team were crucially weakened, as new players such as Rainer Bonhof and Dietmar Danner were not yet able to fill the gaps.

This time experienced players such as Ulrik Le Fevre left the club, replaced by two young Danish forwards Henning Jensen and Allan Simonsen.

Günter Netzer was, with teammates Herbert Wimmer and Jupp Heynckes, part of the powerful German side that won the 1972 European Championship in Belgium.

Despite a temperature of 35° both teams played attacking football, and on both sides the goalkeepers, Borussia's Wolfgang Kleff and Cologne's Gerhard Welz, were called on to make major saves.

Thus ended one of the major 1970s coach-player associations, with Weisweiler and Netzer, in their last year together with Borussia, winning the DFB-Pokal cup but only finishing fifth in the league.

A consolidated Borussia ended the 1973–74 season in second place, Weisweiler again having managed to infuse good new talent, including future international Uli Stielike, into his side.

In addition, Borussia won its first major European title when, after a 0–0 draw at home, they dismantled Twente 5–1 in the second leg of the UEFA Cup final.

Weisweiler moved in the summer of 1975 to the Spanish top club Barcelona, replacing Rinus Michels, who returned to Holland after four years with the Catalans.

On the field Köln was backstopped by national team goalkeeper Harald Schumacher and led up front by top scorer Dieter Müller, but contained no recognized superstars.

They finished ahead of Weismeiler's old team, Borussia Mönchengladbach, by the narrowest of margins, winning the title by virtue of superior goal difference.

During Weisweiler's tenure at the Cosmos he managed stars Franz Beckenbauer, Carlos Alberto, Johan Neeskens and Giorgio Chinaglia at the veteran stage of their careers.