Between 1968 and 1975, members of the Trotskyist Socialist Labour League, the International Socialists and the Militant Tendency held senior positions in factory union organisations at British Leyland factories in Birmingham, Solihull, and at Chrysler in Linwood and Coventry. This chapter consists of a detailed study of shop steward documents at Chrysler's engine factory in Stoke Aldermoor (Coventry), where the IS had a few dozen members, including Deputy Works Convenor John Worth. It looks at how politics affected IS members’ participation in everyday workplace life. Crucially, rather than looking at their contribution to shop-floor activism as an attempt to “import” ideas from outside the factory, I will show how radical militants were often politicised in ways that reflected feelings with wider resonance amongst their co-workers. The presence of an IS fraction within the plant contributed to the changing politics and social practices of the wider trade union movement within the factory, but was ultimately constrained by the constraints of working solely within the issues which the workforce defined as legitimately “industrial”.