Understanding Differential Gears

How Differential Gears Work

I got into a discussion some time ago about welding a rear-end on a street vehicle. It became clear that the guy I was discussing this with did not fully understand how a differential works. The video below was made in the 1930’s or so and is the best explanation I have seen to date.

The guy I was talking with was a young hot rodder. He had heard that welding the rear-end really helps a ride “hook-up”, but that’s all he knew. No one had explained why this would be a bad idea on the street. Once he understood what purpose the differential serves, he saw the light. My guess is that he’ll someday be able to share this same knowledge with a fellow young hot rodder, and also do more research on his own and teach himself something, and that I can get behind.


Basic points from our discussion:

  • When the rear end is welded, all differential action is eliminated, so both tires turn at the same rate. Steering, especially on dry pavement becomes difficult, unpredictable and dangerous because the vehicle will want to go in a straight line. 
  • In a turn, one wheel will end up slipping, which puts all the axle components under considerable stress, which can lead to broken axles or other components, not to mention tire wear.

Now if you are building an drag race car, off-road vehicle or mud-bogger, welding the rear end may make sense, but not on a vehicle that will be driven on the streets.

NOTE: Forward to 1:50 into the video for the good stuff…

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