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1 / 8 A rear axle with the cover off The propeller shaft brings the engine's turning from the front of the car. The gears in the middle split it between the left and right wheels. Drag to look around.
Drag to turn. Scroll or pinch to zoom.
Guide Parts Controls
01 A rear axle with the cover off The propeller shaft brings the engine's turning from the front of the car. The gears in the middle split it between the left and right wheels. Drag to look around.
02 Pinion and ring gear The 11-tooth pinion drives the 41-tooth ring gear, so the shaft turns 3.73 times for each turn of the wheels. The pair also turns the drive through 90°.
03 The case turns with the ring gear The ring gear is bolted to the case. Whatever the ring gear does, the case and the cross pin inside it do too.
04 Going straight Both wheels turn at 420 rpm. Watch the orange dot on a spider gear: it goes round with the case, but the gear does not turn on its pin.
05 Turning left On a 10 m turn the left wheel slows to 387 rpm and the right speeds up to 453 rpm. Now the spider gears spin on the pin at 53 rpm.
06 Inner wheel slower, outer wheel faster The case still turns at 420 rpm, the average of the two wheels. Move the turn radius slider and watch the bars.
07 One wheel on ice The car is stuck. The left wheel spins at twice the case speed and the right wheel stands still, because an open differential gives both wheels the same small torque.
08 Taken apart Ten parts in all. Drag the Take apart slider in Controls to put them back together.
Propeller shaft Brings the turning from the gearbox at the front. At 50 km/h in a straight line it turns 1,565 times a minute. Drive pinion 11 teeth. It turns the drive through a right angle onto the ring gear. Real rear axles use a hypoid pinion set below the ring gear's centre; this one is a plain bevel. Ring gear 41 teeth, bolted to the case. The pinion turns 41 ÷ 11 = 3.73 times for each turn of the ring gear. Differential case Turns with the ring gear and carries the cross pin. Its speed is always the average of the two wheel speeds. Cross pin A steel pin through the case. The two spider gears turn freely on it. Spider gears Two 10-tooth bevel gears. They ride around with the case and only spin on the pin when the wheels turn at different speeds. Side gears 16 teeth each, splined to a half shaft. Each one drives one wheel. Half shafts Carry the drive from each side gear out to a wheel. They are shortened in the model. Wheels 205/55 R16 tyres, 632 mm across. The orange tag on each tyre shows how fast it turns. Axle housing Cast iron, and full of gear oil in a real car. The rear cover has been taken off here.
