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Magic Motoring Moments
Differentials, Motoring Moment Gael Boardman [ January 2004 ]  History tells us that the mechanical marvel of a geared differential preceded the automobile by many years. Some really ingenious guy “thunk” up the differential and made working models in the middle of the 19th century. Here was a great “future problem solver” with no great immediate use. When the horse pulled the wagon there was no need to appropriate power to speed and distance. The horse had his own internal differential. It wasn’t long after self-propelled stuff began turning up that the differential really came into its own.
Consider the problem of belting or direct-connecting just one rear wheel to the engine. You may have made a soapbox type rig in your youth like that and will agree that one-side drive isn’t great. The single driven wheel spins easily and the vehicle handles poorly. Enter the differential.
You need charts or a cut-away model to fully grasp this clever item. But what it does is to allow both wheels to receive power. And that power is proportioned to the amount of resistance the wheels are receiving back up from the road.
When a car is under power and is going around a curve, the outside wheel has to travel much further than the inside one. But there is more resistance on the inner wheel. Both wheels need power for smooth performance and good handling – and the differential does this. As the wheel resistance increases, spinning gears in a small cage attached to one axle, allows the axle speed to change in relation to the other axle. “Compensation” is the best word to explain the theory but you’ll need to look at some diagrams.
Or better yet, go down to the junkyard and give the guy $2 bucks to let you pull the cover off an abandoned differential. Oh, take the charts and diagrams with you. It isn’t real complicated but the darn thing is so clever that you will be a few minutes sorting it out.
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