Introduction to Differentials


We are differential specialists. We sell them, we build them, we eat, sleep and dream about them – we love differentials. Why – because differentials are what makes a vehicle a 4 wheel drive – they have more than one! They are critically important to the performance and durability of any 4 wheel drive and in our case – Land Rover differentials. We are the premier Land Rover differential supplier in North America

Adding performance upgrades to differentials can be the single most effective off road performance upgrade that is possible to add to a 4 wheel drive. In many cases dramatically improving the performance! This is especially so with Land Rovers since the vast majority of them came equipped with standard open differentials and some of them even have three of them.
We feel that a basic understanding of a differential is important to understanding why they are so important. There are many choices for upgrading the durability and performance and they can be – not inexpensive. Understanding them helps you make informed choices when it comes to deciding what performance and durability upgrades to select and helps you spend you money wisely.
NOTE – Differentials are a fairly technical subject. Hence there is a substantial amount of inaccurate information about them (we estimate 80%!), particularly on the internet and public forums. We encourage you to independently research this subject but feel free to call us to help you sort out the good information from the not so good.
So here is a brief overview of them. Differentials have several functions. The most important is to differentiate between the different distances traveled between two tires on the same axle assembly. Hence, the origin of the name – differential. This difference occurs when you are turning a corner i.e. the outside tire has to travel a greater distance than the inside tire. The same thing happens when a single tire drives over a bump or thru a depression. In the 4WD sport there is a lot of talk about locking differentials. Ironically, in the very early years of automotive history, the development of the open differential was a huge technological improvement as this allowed motorcars to function smoothly and more efficiently.
Additional functions differentials provide:
1) They change the direction of the power being transmitted 90 degrees, from a front to rear rotation, to a side to side rotation.
2) They split the torque generated by the engine, 50/50 to the right side/left side axle shafts.
3) They also multiply the torque via different gear ratios
All of these things are happening simultaneously.

MAJOR DIFFERENTIAL COMPONENTS
A differential has three major components:
1) the DIFFERENTIAL HOUSING
2) the RING AND PINION GEARS
3) the DIFFERENTIAL CARRIER

Let’s briefly look at these in more detail. More detailed explanations are found under the specific categories.

1) DIFFERENTIAL HOUSING – this is the large component that holds everything else. They are usually cast iron of varying degrees of quality with nodular cast iron being the highest. They can also be made of other materials such as aluminum, although rarely for 4 wheel drive applications because unsprung weight is not a big issue with 4 wheel drive vehicles. A housing may be a separate piece that is bolted into an axle case or it may be integral with the axle case itself. The separate style are informally referred to as, drop outs, pumpkins or third members and technically as Hotchkiss styles. The integral version is referred to as a Salisbury style, named after the American company that originally designed it – the Salisbury Axle Company. This company eventually evolved into the Dana Corporation. If you are into Land Rovers and we assume you are if you are reading this, and someone mentions a Salisbury axle, you immediately imagine a rear axle assembly from a long wheel base model between the years of 1967ish until 2001. In reality, there are many makes of vehicles that have Salisbury style axle assemblies. Some of them even refer to them this way. As an example, early Jaguar cars have Salisbury axle assemblies. In the USA, a Dana 44, Dana 60 or Corporate 14 Bolts are Salisbury style axle assemblies, although Americans have gotten away from using this term. Jaguar Salisbury axles are based on Dana 44’s. Land Rover Salisbury axles are based on Dana 60’s.

Normally when modifying and upgrading a differential, many people do not realize that there are some additional durability enhancements available. For Rover differentials we can Thrust Bolt them, which is a ring gear support system which prevents ring gear deflection. For Salisburys, heavy duty inspection covers can be used to provide additional rigidity to the axle case helping to insure proper alignment of all of the internal components.

2) RING AND PINION GEAR, also known as the crown wheel and pinion gears. These are a very specialized gear design and different from other common types of gears such as helical gears found in things like transmissions and transfer cases. The function of these gears is twofold. First they are the component that changes the rotational direction of the torque. Second they multiply the torque by varying the gear ratio thru different combinations of gear teeth. There is one pinion gear and one ring gear or crown wheel per differential. They are manufactured as a set and the individual gears should never be interchanged.

Whether you start modifying your Land Rover for improved off road performance with options such as larger tires, or using it for more specialized functions such as towing or expedition usage, changing the differential gear ratio is one of the most effective methods for maintaining or improving the performance of your Rover.
For a more detailed discussion about this topic follow this link to see our technical discussion about Differential Gearing

3) DIFFERENTIAL CARRIER. This is the component that makes a differential differentiate i.e. this is the part that actually provides the differential action. When people refer to “getting lockers” or a locking differential, what they are really talking about is getting a locking differential carrier.

Understanding differential carriers is very important for two major reasons – durability and performance.
Durability is an important factor with most Land Rover differentials because if you aggressively off road a stock late model coil sprung Land Rover until something major breaks, usually this component is the cross shaft in the stock 2 pinion differential carrier. So upgrading your carrier can eliminate the most common major mechanical failure you are likely to experience. This is in addition to the major off road performance improvement.
Traction enhancing differentials are frequently the most effective off road performance upgrade possible resulting in dramatic increases in performance!
Follow this link to learn more about them (——).

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