"Take a look at the stock from where it's coming and where it's going," he said on "Squawk on the Street."
Shares of the engine maker have declined about 35 percent this year and were down more than 6 percent midmorning Tuesday.
CMI stock performance in 2015
Cummins' stock was downgraded to "underperform" by Bank of America Merrill Lynch on Tuesday, citing lackluster earnings moving forward and a slowdown in the Chinese economy.
"If you own Cummins, what they're saying is this is a recession in trucks," Cramer said.
"These guys are the best there is and, if the best there is is having trouble, you can only imagine what's going on at Joy, which also got a [downgrade]."
The bank also reduced its rating on Joy Global from "neutral" to "underperform" on Tuesday.
Disclosure: Cramer's trust did not own Cummins or Joy Global shares when this article was published.