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What: Shares of Trinity Industries (TRN -0.93%) rallied on Friday and were up 10% at 2:45 p.m. EDT.

So what: Driving Trinity Industries' rally was a SEC filing showing that billionaire investor Jeffrey Ubben's ValueAct Capital bought 10.4 million shares in the company, which is equivalent to a 6.8% stake. Further, ValueAct stated that it intends to talk directly to the company's management team to "discuss ways to enhance shareholder value."

Despite today's rally, shares of Trinity Industries are down more than 18% over the past year after a slowdown in the industrial economy put pressure on several of Trinity Industries' business groups. Its rail group, for example, saw revenues slump 37.6% last quarter thanks to lower deliveries, while that segment's backlog slipped from $4.72 billion to $4.29 billion. Trinity's railcar revenue slump was a bit steeper than that of rival Greenbrier (GBX -0.78%), which saw its revenue drop 8.4% last quarter. That said, Greenbrier's new railcar backlog took a similar hit, sinking from $4 billion to $3.6 billion.

Unfortunately, it's not just Trinity's rail group that's struggling. Sales from its inland barge group, energy equipment group, and construction products group were down 37%, 14.7%, and 3.6%, respectively, over the past year. The only positive was the railcar leasing and management services group, which saw a 24.6% bump in revenue.

What's clear is that the company's diversification does not appear to be helping it overcome the current headwinds hitting the industrial sector. While the company is working to address that by repositioning, streamlining, and aligning its manufacturing operations with demand, that has yet to pay dividends. Instead, ValueAct Capital likely sees another path to enhance value, which could include pushing management to jettison some of its business groups.

Now what: From the looks of things, ValueAct Capital is seeking to shake things up at Trinity Industries. That said, there's a big difference between taking an active stake and taking meaningful action. As such, investors should be careful before jumping onboard with the stock just because an activist investor is involved. Given the economic headwinds that could continue to impact Trinity, it could be difficult for even the best activist to enhance value when sales are slumping because of factors outside the company's control.