Lockers

Differential

There are many options available to lock the differentials of an MQ Patrol. This document aims to identify the common options and give info about them. It is not a how to and does not cover installation.

Some companies providing aftermarket lockers include;

FYI, all front diffs are C200 model. The standard Australian rear differential is the H233, and possibly some late-model MK had the H233B. Some other countries feature C200 rear. All countries use H260 as the heavy duty model. To identify your rear differential, refer to the Diff Info wiki-page for specs and pictures.

About Lockers

The standard ‘open’ differential centre in many vehicles allows the wheels to have different speeds, which is ideal for cornering (when the inside wheel would travel a shorter distance than the outside wheel). This is not ideal offroad though, because when 1 wheel looses traction, all of the power is transferred to that wheel. This effectively means that axle and wheels are providing no movement. If this where occurring to the front and rear at the same time, you would be stuck.

Lockers aim to overcome this flaw by keeping both wheels powered, allowing obstacles to be overcome. They do this in different ways.

Types

LSD

LSD stands for Limited Slip Differential, which also explains its functions. They intend to keep the speed between 2 wheels as close as possible, allowing the vehicle to keep moving. Within an LSD, there are often clutch packs within the centre that ‘grip’ the 2 wheels together. This still allows the wheels to differentiate, which makes them suitable for road driving and corners.

Whilst their design does provide traction in more circumstances than an open centre, they often wear out and require the clutch plates to be replaced. If the LSD does wear out, they effectively become an open diff.

These were a factory option to the rear differentials of MQ Patrols. They are available second hand and often quite cheap.

Auto-Lockers

These lockers provide a mechanical lock between the wheels. This keeps the power to both wheels at most times. The ‘auto’ part refers to the lockers ability to disengage, often when it sense side loads on the axles. This means the locker can unlock and function normally around corners etc.

Examples of these include the Lokka and Lockright. They are often priced around $500 AUS, far cheaper than the part-time lockers, but more expensive than the LSD.

Part-Time Lockers

These are also a mechanical locker, but instead of automatically (un)locking as per above, this is controlled by the driver. In the case of the ARB Air Locker, this is achieved by supplying compressed air to the diff centre, which locks the centre. This means during most situations, the diff acts as a normal open centre, providing excellent cornering etc. When a hard obstacle is encountered, the diff can be locked to overcome it.

One downside to this arrangement compared to an auto-locker is when underestimating an obstacle. The driver may attempt an obstacle without locking the differential, and become stuck. They may then have to retry the obstacle with the lockers engaged. This increases the chances of the vehicle becoming damaged. Auto-lockers, on the other hand, would be engaged prior to attempting the obstacle, meaning it could be conquered first attempt.

The ARB Air Locker is a part-time locker. For a complete system, they are priced well in excess of $1,000 AUS. This is the most expensive locker option.

Full-Time Lockers

These lock the wheels together all of the time, providing no ability for the wheels to have different speeds, which can effect cornering (refer vehicle control section below for more info). These are also the harshest locker to the driveline and can cause axles to snap. They are (probably) illegal for road use in all states of Australia.

There are a number of ways to achieve a fully locked diff.

Welded: This involves welding the spider gears within an open differential together, which means they can no longer turn and hence allow the wheels to turn at different speeds. This is a very cheap way to lock the wheels, only requiring a bit of welding.
Mini-Spool: This is a solid 1 piece unit that replaces the spider gears within an open centre, keeping the wheels locked. They are fairly cheap and would be a bit stronger than a welded diff. They can also be swapped from one diff centre to another, or even be replaced by different locker.
Full-Spool: This replaces the whole centre, with a 1 piece unit. These are more expensive, but also stronger than a mini-spool.

Effect(s) on Vehicle Control

Open centres and part time lockers allow proper vehicle control on road. Auto and full lockers do effect the vehicle in negative ways. The below paragraphs are a basic description of the problems faced by auto and full lockers. It should be noted that while LSD’s provide very similar control to an open center, they technically suffer the same problems as auto and full.

Front

It is a common misconception that the steering will be dangerous at all times with a front locker. In the case of an MQ, this is not true.

When the wheels are engaged to the axles (ie hubs locked), the steering will be worse. This is because the wheels need to travel at different speeds around corners. An auto locker should unlock to provide acceptable steering, however a full locker will not. This will reduce the turning circle of the vehicle. Sometimes it may be necessary to exit the vehicle and unlock a hub, allowing the vehicle to negotiate a tight turn. Some people consider this a nuisance, others accept it because they know they have achieved wheel lock on the cheap (ie welded).

The locked wheels will also provide a ‘tracking’ effect, wanting to pull the vehicle into a straight line.

It should be noted that part time lockers when engaged will have the exact same characteristics. So for example, when attempting to turn on a hard hill with the diffs locked, both cars will steer the same.

When driving on road, the wheels would not be engaged to the axles (ie hubs unlocked). This means the wheels can turn at different speeds, not effecting the turning ability at all. Hence, they are perfectly safe.

Rear

Unlike the front, the rear wheels cannot be disengaged from the axles. This means the locker is always effecting the vehicle. Locked rear differentials reduce the vehicles turning circle, as the wheels cannot travel at different speeds. This often results in one wheel ‘skipping’ around a corner on road. An auto-locker should overcome this problem and unlock itself.

In wet weather, the locker can also induce over-steer, especially if the vehicle is accelerated around a corner. This is not a significant problem, but does require the driver to know what will happen and change their driving style to suit (or learn to drive sideways).

Options for C200 (Standard Front)

Factory rear LSD was available for the MQ Patrol. The same LSD centre can be used in a front differential.

Nissan used the C200 in many vehicles. It also produced an independent version, the R200, which have the same centres. According to the ARB catalogue, the following vehicles use the C200, so any factory diff locks/LSD available for those vehicles will be compatible.

Rear diff of 86-97, 4cyl engine Pathfinders, Xtera, Frontier and Navara.
Front diff of 86-97, 6cyl engine Pathfinders, Xtera, Frontier and Navara.

It is worth noting at this point that the clutch discs within C200 are the same as those in H233 diffs.

The ARB Air Locker model number is RD107. Lokka are available, model number is unknown. Lockright do not show a listing in their product catalogue, probably not available. It is unknown if mini/full spools can be purchased.

Options for H233 (Standard Aus. Rear)

Factory LSD was available for the MQ Patrol.

The H233 was used only in the MQ Patrol. This means their are no lockers available from other vehicles.

The ARB Air Locker model number is RD04. Lokka are available, model number is unknown. Lockright do not show a listing in their product catalogue, probably not available. It is unknown if mini/full spools can be purchased.

Some people suggest that H233B were used in the rear of some MK Patrols (not all!). This is the same type as the front diff of a GQ/GU. The ARB Air Locker model number to suit is RD136. Lokka are available, model number is unknown. Lockright model number to suit is unconfirmed, either ‘3210 LR’ (likely) or 3220. Refer to this Patrol4x4 discussion. It is unknown if mini/full spools can be purchased.

Options for H260 (Heavy Duty Rear)