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We’re Coverin’ Your Rear!

Taking a look at where the torque makes a right turn.

Story Andy Bolig - June 19, 2011 09:00 AM

ImageDave VernaDave Verna

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There are MANY areas on our beloved autos that get taken for granted. Not that we intend to neglect them, it’s just that they continually operate without any objections for so long before they throw us a curve ball.

Take the rearend in YOUR car. How old is your car and when was the last time you changed out the fluids in it? Even if you still hold to the old idea of changing your engine’s lifeblood every 3,000 miles or three months, try and think back to the last time you considered the fluid in that differential?

When you think about all that goes on “back there,” it’s easy to see why we SHOULD change the fluid more often. Here we are, using various means to imbibe our cars with more power, torque and traction, many times, without even a second thought to how our rearends will handle it, let alone, divide it evenly among both rear tires. When you think about the constant contact area by which that power tries to get to the tires, it becomes really interesting. While we throw around various sizes of ring gears and the number of teeth that they contain, the truth is, all that torque is using only a small number of those teeth at any given time. Look at the contact areas in Dave Verna’s story on an 8.75-inch rear differential rebuild and you’ll see how small that area really is. Keep in mind also that the pinion gear only rides on a couple of ring gear teeth at any moment.

Not only do we want our rears to be tough, but we want quiet also. While the whine from a straight-cut transmission gear might send the testosterone meter pegging, hearing a similar noise from the differential can make all your friends point and stare. Terms like preload and backlash flow around in this lost art of setting up a differential like the ingredients of some secret potion. In reality, they are quantifiable figures. Once understood, the seasoned rear setup chef can use them and make slight variations to the recipe to suit his own tastes.

This month, we’re looking at several different ways that we can not only upgrade our respective rears, but also make them last a little longer too – even under the additional power that we might try to squeeze through them.

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