While Fools should generally take the opinion of Wall Street with a grain of salt, it's not a bad idea to take a look at particularly stock-shaking analyst upgrades and downgrades -- just in case their reasoning behind the call makes sense.

What: Shares of Johnson Controls (NYSE:JCI) slipped 2% today after Morgan Stanley downgraded the auto-parts and building-efficiency specialist from overweight to underweight.

So what: Along with the downgrade, analyst Ravi Shanker lowered his price target on the stock to $40 per share (from $45), representing about 6% worth of downside to Friday's close. The stock soared over the past year as management's turnaround initiatives have gained plenty of traction, but Shanker thinks the valuation now has too much optimism baked into it.

Now what: The stock's upside certainly seems limited in the short run. "We moved JCI near the top of our rankings a year ago because we saw far more scenarios where JCI could win than lose," Shanker said. "However, with execution back on track, a new CEO lobbying for change and the stock at $43, expectations into the analyst day may be too high." Of course, with the stock still off its five-year highs and trading at a forward P/E of just 12, Johnson Controls still seems like a reasonable long-term proposition. 

Fool contributor Brian Pacampara has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.