A rear locker: the biggest traction gain, and the one that has to be switched off

DrivetrainSafety-criticalCost$$$–$$$$Difficulty 5/5FitsGen 3

Safety notice — Steering.

This affects a safety-critical system. Reference material only: for safety-critical work, consult a qualified mechanic.

Esto afecta un sistema crítico para la seguridad. Material de referencia únicamente: en trabajos críticos para la seguridad, consulte a un mecánico calificado.

Community consensus. This entry is not backed by factory documentation — treat its values and steps as a starting point, not as if they came from the factory manual.

Consenso de la comunidad. Esta entrada no se apoya en documentación de fábrica — tome los valores y los pasos como punto de partida, no como si vinieran del manual de fábrica.

A selectable rear locker is the single largest traction change available to this truck, and unlike a lift or a tire it does nothing at all until you ask it to. The manufacturer cited below describes the mechanism precisely: activated, it stops the differential gears turning and therefore stops the two rear axle shafts turning independently of each other; unlocked, it behaves like an ordinary open differential. The rear application for this generation is listed for the whole 1999-2006 span across the common trims and is stated to suit all factory ratios, so a locker and a ratio change are independent decisions. The kit as sold is a differential and its switching hardware; the air to operate it is a separate purchase, which the manufacturer says in as many words.

What it needs first

Nothing else has to be done first.

What it breaks or affects

Everything below is a consequence of fitting this, not a reason against it. Read it before you buy, not after.

System	Consequence	What happens
Steering	Gets worse	The manufacturer's own description is that activation prevents the axle shafts from turning independently of each other — which is exactly what has to happen for the two wheels to fight a turn. The same page also claims the unit provides traction «without affecting on-road drivability or driveline wear»; it does not say that claim is about the unlocked state, but we read it that way, because the mechanism it describes one paragraph earlier cannot be true of a locked axle on grippy pavement. That reading is ours, not the vendor's. Engage it where there is no grip to give up, and unlock it before you are steering on a surface that has any.
Drivetrain	Has to be reset	The kit is a replacement differential centre with switching hardware, not a bolt-on accessory: the differential has to come out, be set up and go back in. That is where most of the cost and all of the risk lives, and it is why this job sits at the top of the difficulty scale.
Electrical system	Has to be reset	The manufacturer states that an air compressor is required for operation and is sold separately. Budget the compressor, its mounting, its wiring and its current draw as part of this modification rather than as a later accessory — an installed locker with no air is a very expensive open differential.
Drivetrain	Has to be reset	The front application listed in the second citation excludes some 28-spline axles that use a smaller ring gear, and excludes one engine-and-transmission combination outright. Check what your truck actually has before planning a pair; the rear listing's broader coverage does not carry over to the front.

The honest tradeoffs

Everything good about a locker happens when it is engaged, and everything to be careful about happens for the same reason. With both rear wheels tied together the axle resists being steered, so it is a low-speed, off-pavement tool that you switch off before you are back on a road with grip — the manufacturer does say the unit behaves like a conventional open differential when unlocked, which is the state its no-compromise drivability claim has to be about. It is also deep work: the differential comes out and goes back in as a set-up job, which is a specialist's work with a specialist's tooling, and a set-up done badly is a whining, short-lived differential rather than a bad afternoon. Then there is the air: no compressor, no locker, and the compressor is its own install with its own current draw and its own mounting problem. The front is a separate and narrower question — the front application carries two explicit exclusions in the second citation, one about ring gear size on some 28-spline axles and one about a particular engine and transmission combination, so confirm your own axle before assuming a front locker is available to you. Weigh a locker against tires honestly: a locker helps when one wheel has no grip at all, and better tires help everywhere. Drivetrain work of this depth belongs with a qualified mechanic.

Safety notice — Steering.

What it needs first

What it breaks or affects

The honest tradeoffs

Sources