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What is a differential?

A differential is the driving-axle gear assembly located in the center housing between the driving wheels on rear-wheel drive vehicles, or as part of the transaxle on front-wheel drive vehicles or between front and rear differentials on all-wheel drive vehicles. The differential transmits power to the wheels while allowing each wheel to rotate at different speeds, such as when turning a corner.

Why is it needed to lock the differential in certain conditions? If a wheel loses traction (the wheel is on ice, show, mud, or raised in the air), an open differential will send all available engine power to that wheel. The wheel will spin, but the car will not move. So even if a vehicle has all-wheel drive, but neither of the three differentials can be locked, it is enough for just one wheel to lose traction (to spin) and the car will not be able to move.

So, to get the car moving, it is necessary to lock a differential. Locked (or limited slip) differentials make (or try to make) the wheels to spin at the same speed, syncronously. This transfers torque from the wheels that spin to the wheels that have traction. Ideally, a vehicle should be able to fully lock all three differentials (center, rear, and front) - in this case the vehicle would be able to move as long as just one wheel has traction.

Figure: Free differential

differential

Figure: Limited slip differential

Read more: How a differential works

Last updated: 08-Apr-2010 17:42


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There are 3 comments
Igor
January 06, 2010 - 11:37
Subject: Crackle

When I push a button to block a central deff. (Toyota LC-105), and trying to turn after the defferential clocked, I can hear strange noise like, would say a crackle from the front wheels. What can it be?
Thanks beforehand.

Derek Thomas
March 03, 2009 - 04:10
Subject:

What oil should i use in my all whel drive rav 4 rear differancal
Year 1996
looking foward to hear from u.

Reply to Derek Thomas
awd.ee
March 03, 2009 - 18:35
Subject:

Well, I don't know. I may want to refer to the service manual or ask this question on a RAV4 forum.

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