Retrotechtacular: The Differential

Any video that starts off with two minutes of motorcycle formation riding has got to be good. If the grainy black and white video didn’t tip you off that this was made in a different time the helmetless riders standing on the seats of moving motorcycles certainly would have. But there is a purpose to this exposition. A single line of motorcycles riding shoulder to shoulder as they go around a curve illustrates why a differential is necessary and soon after you’ll find out how one works.

Two wheels mounted on one axle need to turn at different speeds as a vehicle goes around a corner or one of the wheels must slip to accommodate the speed difference. The differential is necessary to allow for these different turning rates while still letting both wheels connect to the power train. We were surprised to learn from the video after the break that early automobiles got around this issues by powering only one of the four wheels.

This instructional video is a prefect compliment to the fluid coupling video we saw in the last installment of Retrotechtacular.

[Thanks Matt via Auto Week]

22 thoughts on “Retrotechtacular: The Differential

    1. I thought so, too. I mean, I knew the purpose a differential served but it was always that big sealed lump in the middle of the axle where spinny geary type things happened, but I really didn’t grasp HOW it did it’s magic. This was a great video

  1. Not all differentials use three bevel gears like that. The Austin 7 uses six straight cut gears (acting as three pairs across the diff) inside the diff carrier meshing with straight spur gears on the ends of the axle half shafts. Took me a while to get my head around it! That arrangement allows you to do an interesting thing if you break a half shaft which will cause you to lose drive as all the power then goes into the broken side which will spin uselessly. You basically remove the broken sides hub and shove the broken half shaft into the diff until the spur gear meshes with the three gears on the opposite side of the diff. Then you use a wheel nut as a spacer inside the axle tube and reattach the hub on the broken side. This will lock the diff up and transmit power to the unbroken side allowing you to limp home with one wheel drive!

    Almost impossible to describe unless you see one.

    1. Well obviously they’re only talking about the classic open diff, the simplest and most common one. There are many types of differentials and far more implementations of each type. Incidentally, it uses four bevel gears here.

  2. I love these old videos! And especially all the little models they make to demonstrate it! Today we’d just use 3D CAD to show diagrams but they went all the way and built them! The one similar to this on hardware computers (using warships and maths) is fascinating!

  3. Hear hear, more vintage science or engineering videos please HaD! Fantastic!
    My, and I suspect most people’s exposure to diffs came from RC cars, my old RC buggy had limited slip diffs. Explain that 1930s (I bet it can too)!

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