Differentials Explained - Standard or Open Differential

A standard differential, or what is referred to as an open carrier, is what comes OEM on many vehicles.  This is what holds the ring and pinion in place and gives the vehicle it's final drive ratio.  It is responsible for transmitting power from the driveshafts to the vehicles wheels to ultimatly make it move.  The open differential is composed of six parts: 

·        Differential Case

o       Holds the differential Gears

o       Also carries the ring gear so surname is ‘carrier’

·        Differential Side Gears

o       Transfers power from the case to the axel shafts

·        Differential Pinion Gear

o       Allows each side gear to move independently of the carrier

o       Crawls over the side gears; often-called a ‘spider gear’

·        Differential Pin

o       Holds the differential pinion gears in place

o       Locks the side gears in place

o       Retains C-clips in side gears for some applications

·        Ring Gear

o       Attached to the case via bolts to make the case spin

·        Pinion Gear

o       Attached to the housing via bearings

          o       Transfers power to the ring gear via the driveshaft

When the vehicle is being driven in a straight line, there is equal force on the side gears.  This does not allow the pinion gears to turn and thus, the ring gear spins both wheels.  Once there is enough resistance on one tire to slow down, or speed up that tire then the pinion gears fall into play and allow the two side gears (attached to the axle shafts) to rotate at different speeds.  This is very good for turning the vehicle whether it be a front, rear, or four wheel drive vehicle.

Whenever a vehicle negotiates a turn, the outside wheel must travel farther (turn faster) than the inside wheel. This is accomplished by a series of gears that allow the outside wheel to turn faster than the ring gear, while the inside wheel turns slower than the ring gear. This differentiating action is very simple in a standard open differential and works great for most of the vehicles on the road today.  However, they do suffer greatly when encountering a low traction or slippery surface.

When a vehicle with an open differnetial encounters a low traction surface, it directs power to the wheel with the least amount of traction.  This results in the wheel on the low traction side spining while the opposite wheel with high traction receives little to no power.  This is due to the low traction wheel not providing proper resistance to the side gear to spin the carrier and transfer power to the oppposing wheel.  The carrier pinion gears and the carrier simply rotate around the side gear with the most traction and nothing gets passed on. 

 

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