Hi maccaron and welome.
Which is better between a rear diff lock and traction control is a raging debate with more questions than answers, which might indicate that they offer similar off-highway abilities over all, with each having their fortes and their issues.
The following summary is my opinion (for the Gen 3) and might be of some help:
Rear Diff Lock
Advantages
- Because it is a simple mechanical lock between the lefthand and righthand rear sideshafts, it is possible for the torque split to vary seamlessly and instantaneously between the two rear wheels, depending on the grip underfoot. This means that it works equally well when slowly crawling over boulders and when storming a huge dune.
- All power dissipated by the rear axle is used to propel the vehicle
- It is under control of the driver to a great extent
Disadvantages
- As the name implies, the rear diff lock only acts on the rear wheels. It is quite easy to find yourself in a situation (e.g. climbing an undulating, steep, loose surfaced hill) where you are immobilized with one front wheel lifted and spinning, the other front wheel stationary and the two rears spinning despite having good grip, without being able to generate enough tractive effort to climb the grade. Being able to lock the front diff would make all the difference.
- Some understeer is induced when the rear diff is locked (not a lot, though).
Electronic Traction Control
Advantages
- The system acts on all four wheels and can assist in preventing spin-out on any of them.
- The system is part of a setup that also includes vehicle stability control (VSC), which helps to keep the vehicle under control at high speeds by selectively applying the individual wheel brakes and reducing engine power based on inputs received from the throttle position sensor, the steering angle sensor and an accelerometer.
- Minimal interference with vehicle steering
Disadvantages
- Electronic traction control is a reactive system that has a response time (i.e. there is a lag in its operation). This might be enough to bog you down in a situation where a little momentum is required and things happen a little faster.
- The system is under full electronic control, with very little input required (or indeed possible) from the driver
- If the VSC system is not disabled, the vehicle can bog down very easily in loose sand, due to the systems overenthusiastic use of the wheel brakes and power reduction to kurb what it perceives to be alarming spinning and sliding, but which is normal in sand driving.
- If the VSC system is not disabled, it is possible to bog down when trying to pull rapidly onto a tar road from a dirt side road as the system cuts power to prevent spinning and leaves the vehicle in the lurch in the path of oncoming traffic.
- The VSC system automatically turns itself back on whenever the vehicle ignition is turned off and on again or when the speed exeeds 80km/h (I think). This can catch one out.
- The system depends upon the ABS braking system. The hydraulic brake booster can only cope with so much continuous use and it will eventually (after 10 to 15 minutes of continuous use) shut itself down to prevent overheating. It announces that this is imminent via a loud buzzer. When this happens, you are left with no traction aids and open diffs until things have cooled down.
- Accelerated brake wear
- A small wiring fault or ABS sensor fault could lead to the system shutting itself down and then you are back to open diffs...
- Nominally 50% of the power dissipated by each axle will be in the form of heat generated by the brakes whenever the traction control is operating
Some general musings:
A rear diff lock will have the upper hand in the following type of scenarios where vehicle speed is relatively high:
- Thick sand
- Thick mud
- Steep undulating climbs
Traction control will have the upper hand in the following type of scenario:
- Slow crawling over very uneven terrain.
All the Gen 3 SWBs officially imported via Mitsubishi Motors SA (or the few that were brought in by SAMCOR) are of GLS spec. Up to somewhere during 2003 they all came with the rear diff lock. Any 3.5 SWB will have a rear diff lock. When the 3.8 V6 was launched somewhere in 2003, the diff lock was dropped and electronic traction control (and VSC) was introduced (and side airbags).
In terms of use at speed on gravel roads I think you are correct in saying that the Paj's Super Select system is more sophisticated than the Landy'a full time 4x4 system with lockable open center diff. The Paj has a viscous limited slip diff in the center that prevents spin-out (front to rear), but does not generate wind-up. Pajero Gen 3s with the rear diff lock actually have a lockable Torsen limited slip diff in the rear, so even when it is unlocked, it prevents complete rear axle spin-out as long as both rear wheels have some grip.
Oh and Dave, real men don't use traction control. Always keep it real
