Need to learn some rear end basics.

J

JimNNN

Well-known member
I was reminded of how little I know about rear ends yesterday (just one of may subjects I know very little about.) I had my '65 T-Bird up on jack stands, and tires removed. ****** in park, so drive shaft doesn't move, but I could rotate rear wheel (drum.) To my surprise, while I rotated the drum, the brake drum on the other side rotated in the opposite direction. I presume that's the way it's supposed to work...or maybe not...I don't know. The drive train seems to function like it's supposed to while driving. As I recall from the data plate it's like a 3.25 gear ratio, and I believe it's a 9 inch rear end. What's going on with the rotation?
 
That is normal, it has to do with the differential gearing. In fact if I'm remembering correctly without this characteristic, with a solid axle the innermost wheel during a turn would skip and hop. Recall the outer wheel on a given axle travels farther/faster than the inner wheel. I think that's called an "open differential", versus a locker or positrac or whatever Ford called it.

I don't claim to understand it, but this is also how or why no traction is obtained on dry pavement when one of the read wheels is spinning on ice. A "2 wheel drive" is really a "1 wheel drive" with an open differential. A "4 wheel drive" can have a similar problem.
 
When the differential spider gears have contact with both axle side gears and the wheels are off the ground, the rotation of one side gear makes the other go the opposite way unless the whole carrier is capable of turning.
 
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