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Now You Know: What is a Rear Differential on a Car and Why Do We Need One?

It’s from 1937 but in 9 minutes, you’ll understand it as plain as day … This is exactly how everyone should explain everything …

Note, there is about a 2-minute motorcycle stunt show that seems to make no sense but slowly reveals why they started that way …

I think I could fix a car if they explained every other function of a car this clearly.

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13 April 2011 Design 12 Comments


  • por356 says:

    Wonderful! Very easy to understand and beautifully shot. I have been a car nut all of my life and I still learned something. Of course, I am prejudiced because my first car was a 1937 Chevrolet like the sedan shown at the end (and yes, it was a very old car when I got it, I am not THAT old!)

  • danrio says:

    A dated, but easy to understand demonstration of the mechanics of the differential. Thanks for digging this one up!

    It brings to mind an incident I experienced at a local (brand name)car repair facility several years ago. I accompanied my wife who was picking up her ’98 Toyota Sienna. At the counter, I looked over the repair bill and stopped at this one item: #39 for “pumpkin” service. When I asked the mechanic what that involved, he explained that they had removed the drain plug from the differential(aka “pumpkin”, because of its shape), and checked and corrected the oil level as well as inspected the unit for wear. Boy, was he surprised when I told him that he couldn’t have done that on my wife’s front wheel drive van! He consulted his manager and took the charge off the bill.

  • Dunroamin says:

    This movie is awesome…it reminds me of the Zinc Oxide and You from Kentucky Fried Movie 🙂
    Up Next: the Buick Skylark with posi-traction…or was it without posi-traction

    • buckland-blowouts says:

      Kentucky fried movie!!! Haven’t heard of that in a long time!!!

      Wasn’t Chevy Chase in that one?!?!? OR was it Outakes?

      What a blast!!!

  • NascarFan says:

    Pretty slick, whats next? torque converters?

    • Stig McQueen says:

      Torque converters mystified me for about the first four decades of my life. I could not understand how the transmission could be “in gear” with the engine running and the car stopped. Then I finally realized that a torque converter is like a bowl of cake mix; when you turn on the mixer (engine), the bowl (converter)wants to turn because of the motion of the cake mix (transmission fluid)inside! If you hold the bowl with your hand (brakes), you can keep it from turning without stalling the mixer!

      Next up: Non-linear temporal physics

  • Hostile Takeover Banker says:

    I know all about this from an unfortunate incident involving a whole bunch of plastic. Heat, oil, plastic and something spinning around very fast doesn’t make for a very good mix.

  • Tom says:

    Those old corporate-produced spots are great. How about a limited-slip differential or Audi-type setup where there is a second diff in front for the front wheels?

  • hypercarrots says:

    differential is very important in a drift car

  • pwschuh says:

    Seriously: who doesn’t know what a rear differential is? I’m pretty sure my 14 y.o daughter would be able to answer that question.

  • John in Missouri says:


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