Spinoffs have historically been great investments, and right now a number of companies are feeling the pressure to break apart to unlock more value. These are the stories you should be buying and selling.

With the S&P 500 now down nearly 5% over the last year, companies are looking to unlock value any way they can.

This includes spinning off parts of their business or doing full-blown breakups. Now, spinoffs have historically been great investments.

Joel Greenblatt has one of the best investing track records ever, thanks to investing in spinoffs and other special situations. Greenblatt started his hedge fund, Gotham Capital, in 1985. For the next 10 years, he generated an annualized return of 50%.

He did this by looking for spinoffs that were unloved for a variety of reasons, including the fact that the parent company was just getting out of a “bad” or unrelated business. In that case, institutions generally don't want to own the spinoff and dump it, putting unnecessary pressure on the stock.

However, what about investing in companies before the spinoff process and getting in before the breakup?

Well, that's not always quite as profitable. You really have to do your due diligence when assessing a potential breakup.

Just look Xerox (NYSE: XRX), which announced just last month it would split into a hardware and software business. Shares are now down 9% over the last month.

Then there's Manitowoc (NYSE: MTW), which announced in January of last year that it would split into two businesses: a food equipment company and a crane company. However, shares have fallen 20% over the last twelve months.

The key is that sometimes splitting up a struggling business just means you'll be left with two struggling businesses that are not necessarily any better off. It's about doing your due diligence.

With that in mind, here are five stocks getting breakup pressure that might be worth buying, or selling: