How a car differential works

How a car differential works

Image for article titled This Vintage Film Is Still the Best Explanation of How a Differential Works

How does a car’s differential work? You probably have a vague understanding. Some things turn, some don’t, and somehow the result allows your car to go through a curve without shredding its tires or chewing its own guts. There are gears and other gears, and it’s actually magic. That was the extent of my own understanding, until I discovered… this 1937 vintage educational film† It’s still the best, simplest, most understandable explanation of how a differential works I’ve ever found.

I love this old black and white movie so much, I wrote about it a while back those guys† It’s worth re-presenting to a new audience, because even if you’ve held the guts of a disassembled differential in your hands, you might still struggle to explain how that collection of ring, pinion, and spin gears get power to the ground, and make two wheels on the same shaft spin at different speeds.

Our instructor in this class is Henry Jamison”Jam” Handy, a fascinating character who spent much of his career making educational films like this one. Mostly, they were cleverly disguised ads—most of Handy’s car films were commissioned by General Motors, while others were sponsored by Standard Oil. Regardless of the subject, a Jam Handy movie starts with a simple “how does X work” question and answers it with clear, smart, immediately understandable visual aids. Usually the last minute of the movie is where it becomes an ad – for example, hype up the latest technological advancements you’ll find at your friendly local Chevrolet dealer. But all that leads to that brief sales pitch is general interest, brand-independent knowledge that is absolutely fascinating to car enthusiasts or anyone with a curious mind.

So! Back to the differentials. Of course, this 1937 film doesn’t address the voodoo of limited-slip differentials — we’re just talking single-band open diffs here. But the images and explanations are so simple that a child could understand.

So take 10 minutes and learn the inner workings of something you’ve always wondered about. Even if you already know the ins and outs of differentials, I promise this movie will give you a new perspective on how it all works.