Front Differential Description & Operation (page 4 of 4)

pinion gear changes the ratio.  
 
The differential comprises a pinion shaft and hypoid bevel gear, a crown wheel drive gear with an integral cage, which 
houses two planet gears. Two sun wheels are also located in the cage and pass the rotational drive to the drive shaft 
shafts.  
 
The pinion shaft is mounted on two opposed taper roller bearings with a collapsable spacer located between them. The 
spacer is used to hold the bearings in alignment and also collapses under the pressure applied to the pinion nut. This 
allows the nut to be tightened to a predetermined torque, which collapses the spacer, setting the correct bearing preload.  
 
The pinion shaft has an externally splined outer end which accepts and locates the input flange, which is retained by the 
pinion nut. The opposite end of the output flange has an internal spline which provides positive location for the front 
propeller shaft. The flange has an external O-ring seal which seals against the front propeller shaft shroud preventing the 
ingress of dirt and moisture into the splines. An oil seal is pressed into the LH casing and seals the input flange to the 
differential unit. The pinion shaft has a hypoid bevel gear at its inner end which mates with the crown wheel drive gear.  
 
The crown wheel drive gear is located on the carrier and secured with ten screws. The carrier is mounted on taper roller 
bearings located in each casing half. The bearings are press fitted into the casing and a spacer is located on the outside 
face to set backlash and apply preload to the bearing.  
 
The carrier is fitted with a shaft onto which the two planet gears are mounted. The shaft is secured in the carrier with a roll 
pin. The sun wheels are located in pockets within the carrier and mesh with the planet gears. Thrust washers are located 
between the carrier and the sun wheels and hold the sun wheels in mesh with the planet gears. Each sun wheel has a 
machined, splined, bore to accept the drive shaft. A groove is machined in the bore to locate the snap ring fitted to the 
drive shaft, providing positive drive shaft location.  
 

Differential Operation  

The operating principles of the front and rear differentials are the same. Rotational input from the propeller shaft is passed 
via the input flange to the pinion shaft and pinion gear. The angles of the pinion gear to the crown wheel drive gear moves 
the rotational direction through 90°.  
 
The transferred rotational motion is now passed to the crown wheel drive gear, which in turn rotates the carrier. The shaft, 
which is secured to the carrier, also rotates at the same speed as the carrier. The planet gears, which are mounted on the 
shaft, also rotate with the carrier. In turn, the planet gears transfer their rotational motion to the left and right hand sun 
wheels, rotating the drive shafts.  
 
When the vehicle is moving in a forward direction, the torque applied through the differential to each sun wheel is equal. 
In this condition both drive shafts rotate at the same speed. The planet gears do not rotate and effectively lock the sun 
wheels to the carrier.  
 
If the vehicle is turning, the outer wheel will be forced to rotate faster than the inner wheel by having a greater distance to 
travel. The differential senses the torque difference between the sun wheels. The planet gears rotate on their axes to 
allow the outer wheel to rotate faster than the inner one.  
 

SERVICE  

The oil used in the front differential is Castrol SAF-XO. The oil contains unique additives, which enhance the differentials 
operation. No other oil must be used in the front differential.  
 

Front Differential Serviceable Components  

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Halfshaft seals  

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Needle roller bearing assemblies  

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Chassis bush/fixings  

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Lubricant.