The current economic expansion is one of the longest on record. That's helped to keep the stock market up near all-time highs. But the market isn't always bullish, and investors need to keep an eye out for the downturns that always follow upturns.

Right now, there are some troubling recession warning signs starting to emerge at economically sensitive industrial giants like 3M (NYSE:MMM), Eaton Corporation (NYSE:ETN) and Rockwell Automation (NYSE:ROK).

Here's a quick look at what's happening.

1. 3M's troubling trends

Diversified industrial giant 3M is facing a number of worrisome headwinds today. One of the big ones making the news is the company's legal troubles, as it deals with liability surrounding supposedly faulty products and water contamination issues. However, there's a lot more going on today that has investors spooked, sending the shares down by more than a third from their early 2018 highs.

A notable issue in 2019 has been a change of direction in 3M's "short-cycle" businesses. These are economically sensitive operations that tend to turn down before a recession hits. A prime example is the company's auto-related business, which has been hit by slowing vehicle markets abroad and domestically. The company was so concerned about the outlook for these businesses that it trimmed guidance after the first quarter and started a cost-cutting program.

Management has been seeing some success in its cost-cutting effort, but in its second-quarter 2019 conference call noted that there is still "uncertainty" in the global economy and highlighted that growth trends appear to be "slowing." Although 3M maintained its guidance for the rest of the year, it didn't really do much to reduce the economic concerns that have investors worried about its near-term future.

2. Rockwell's short cycle

It's not just 3M that's seeing weakness in short-cycle businesses. Industrial automation specialist Rockwell has also seen a trend shift. Management noted that organic sales were up 0.5% year over year in its fiscal third-quarter earnings presentation, highlighting strength in its oil and gas, pulp and paper, mining, and life sciences businesses. But the very next bullet point was: "Shorter-cycle weakness: automotive, semiconductor, food and beverage."

The company went on to note that, "Uncertainty with respect to global trade is impacting some customers' investment decisions, particularly those related to the timing of capital investments." The company reduced its organic sales growth projection for fiscal 2019 from 3.7%-5.3% to just 1.5%. That's a pretty sizable downward revision that occurred between just April and July. It's also worth noting that there's only one more quarter left in the company's fiscal year, so investors would be right to wonder if something material is taking shape. While Rockwell is still expecting growth, it is clearly less sanguine about the future than it was just a few short months ago.

3. Eaton is worried, too

Adding to the picture is power specialist Eaton, which has now lowered its expectations twice so far in 2019. The company entered the year expecting organic growth of 4% to 5%. After just one quarter, however, it trimmed that to 4%. The big drivers were reduced expectations in its hydraulic operation, which sells to original equipment manufacturers in industries like construction, and its vehicle division, which has material exposure to trucking. Both of these businesses are highly sensitive to economic conditions.

Unfortunately, the first reduction wasn't enough. When it released second-quarter earnings, Eaton dropped its organic growth expectations to 3%. The big drivers were, once again, hydraulics and vehicles. So whatever weakness started to show up in the first quarter continued to gain steam in the second. Eaton's expectations for its vehicle division are particularly troubling. At the start of the year, management expected an organic sales drop of 1% to 2%, weak but not terrible, but has since shifted to projecting a decline of between 7% and 8% -- a much more troubling pullback.

Not alone...

Industrials are generally pretty cyclical businesses, with their top and bottom lines going up and down along with the economy. Looking at the recent results of some of the largest players in the industry, there's nothing at this point that suggests we are in a recession. But there are some warning signs starting to show up that the economy is beginning to weaken. The news out of 3M, Rockwell, and Eaton provides just a few examples. There are more, if you look closely enough.

The key is to look at the trends and not the absolute numbers, which are still showing overall growth. Although it may be too soon to say we are in a recession, the financial performance of industrial companies like these shows clear signs that the risk of a recession is rising.

Reuben Gregg Brewer owns shares of Eaton. The Motley Fool recommends 3M and Fastenal. The Motley Fool has a disclosure policy. This article originally appeared in the Motley Fool.

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