How does a car differential work? You probably have a vague idea how. Some things turn, some don’t, and somehow the result allows your car to go around a corner without shredding the tires or its own guts. There are gears and more gears, and they basically do magic. That was the extent of my own understanding, until I found this vintage educational film from the year 1937. It’s still the simplest and most easily understood explanation of how a diff works that I’ve come across.
I like this old black and white recording so much I wrote about her a while ago. It’s worth re-introducing it to a new audience, because even if you’ve gotten your hands on the guts of a disassembled differential, you may still have a hard time explaining how that collection of gears from rings, pinions and spiders bring energy to the ground and allow two wheels on the same axle to rotate at different speeds.
Our instructor for this lesson is Henry Jamison “Jam” Handy, a fascinating character who spent much of his career making educational movies like this one. More often than not, these were cleverly disguised advertisements: Most of Handy’s automotive films were made at the behest of General Motors, while others were sponsored by Standard Oil. Regardless of the subject, a Jam Handy movie begins with a simple question: “how does X work?” and it is answered with clear, ingenious and immediately understandable visual aids. Usually the last minute of the movie is where it turns into an advertisement, for example promoting the latest technological advances you’ll find at your friendly Chevrolet dealership. But everything leading up to that short sales pitch is brand-independent, general-interest insight that is absolutely fascinating to car enthusiasts or anyone with a curious mind.
So back to spreads! Naturally, this 1937 movie doesn’t delve into the voodoo of limited-slip differentials; we are only talking about open spreads here. But the images and explanation are so simple that a child could understand them.
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 diffs, I promise this movie will give you a new perspective on how it all works.