Meaning : center differential lock

[robert]

I've heard people talk about rear/front diff-lock and understand the working and purpose thereoff. I am not sure what is a center differential lock - how it works and purpose, because I still struggle to have equal power in both wheels. I have a 1994 Pajero LWB. Can anyone take me out of my mistery ? Thanks.

Robert.

[Gerrit Loubser]

Robert, have a look at my reply to another similar question in this thread, which might help.

The Paj has the ability to run in 4wd on tar, something that the 4x4 bakkies typically can't do. In order to make this possible, the Paj has a center diff (which is actually also a viscous limited slip dif, thus making 4H just about the most perfect dirt road set-up possible). When the going gets really tough, the Paj's center diff can be locked (4HLc, 4LLc), which locks the front and rear propshafts together and thus places it in the same state as the typical 4x4 bakkie would be in when 4H or 4L is selected.

Although the Paj's rear limited slip diff (LSD) is better than an open diff in cross-axle situations, its performance is very limited when one wheel on the rear axle is in the air. It is possible to enhance its performance in these situations by applying the park brake or even the lightly applying the foot brake, because the Gen 2 Paj's limited slip diff is of the ramp loading type, i.e. the lock-up ratio is dependent on the amount of torque transferred (which is essentially nothing when a wheel is lifted and which can be increased by generating some resistance to rotation using the brakes). Be aware that the little drum-in-disc park brake shoes are tiny and they wear quickly if you use them a lot to enhance the LSD's operation. You also have to tug on the park brake lever quite hard...

Unfortunately Pajeros are not blessed with the best ability to keep all four tyres on the ground in cross-axle type situations (called "flex" by many). The upshot of this is very tidy handling on tar as well as dirt roads for a vehicle that is quite tall and heavy.

At the front the Gen 2's flex is somewhat better than many torsion bar sprung bakkies due to the long torsion bars employed, but overall the front roll stiffness is quite high and contributes only a small percentage of the total flex.

At the rear the Gen 2 has a beam axle, which bodes well for flex, but unfortunately the dual trailing arm plus Panhard rod suspension location system has high inherent roll stiffness, that increases rapidly and non-linearly as roll increases. Five link systems (as in the rear of the Trooper, Prado or coil sprung Cruisers & Patrols) typically allow much more rear axle flex than the Paj's system.

It might be very worthwhile to experiment with the improvements in flex obtainable by disconnecting either one or both of the anti-roll bars. These devices are designed to provide additional roll stiffness without adding to the vertical suspension stiffness, so they fight flex directly. The greatest improvement in flex will probably result from disconnecting the front anti-roll bar, but be aware that it is not advisable to drive on the tar at high speeds with the front anti-roll bar disconnected. Quick-disconnects are worth investigating...

Adding a rear diff lock does improve the off-road mobility of any vehicle massively, especially one with limited flex. It might be possible to retrofit a locking rear diff from a later model Paj (Blister Fender), but this will depend on the final drive ratio in yours.

Another option is adding a front axle diff lock, which achieves much the same thing as adding a rear diff lock, but does interfere with steering more when engaged. You could fit an ARB selectable air operated diff lock (expensive) or an automatic locker to the front dif.

Or you can decide to enjoy your vehicle as it is, learn how to get the most from it and hone your skills...

[robert]

Gerrit.

Absolutely clear. I'll think I will try the cheapest obtion, namely to apply the park/foot brake. I am not a seriuos (exstreme) 4x4-er, so the front/back difflock obtion is not necessary. I agree, will just enjoy my standard vehicle.

Many thanks.
Robert.

[SimonB]

Gerrit.

Absolutely clear. I'll think I will try the cheapest obtion, namely to apply the park/foot brake. I am not a seriuos (exstreme) 4x4-er, so the front/back difflock obtion is not necessary. I agree, will just enjoy my standard vehicle.

Many thanks.
Robert.

Robert, this technique requires considerable practice because timing is crucial. When you get it right though, the smug look is priceless.