Shares of Cummins (CMI) are down about 4% Tuesday after the company beat on earnings, but missed on revenue expectations. Sales declined 9.1% year over year. 

"The truck story is a bad story" and Cummins' results were bad too, TheStreet's Jim Cramer, co-manager of the Action Alerts PLUS portfolio, said on CNBC's "Stop Trading" segment. 

The results were disappointing and Eaton's (ETN) weren't good either, Cramer noted. 

Arconic  (ARNC)  -- the separately traded entity which was spun off from Alcoa  (AA) -- CEO Klaus Kleinfeld said the trucking industry wasn't as strong as some had expected and he was right, Cramer added. 

Investors should be careful with truck-based companies, because right now the "truck business is a bad one," he concluded. 

At the time of publication, Cramer's Action Alerts PLUS had a position in AA. 

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