SELECTING 4x4 ON TAR

Car (South Africa) - - TECH -

I have a Hilux with selectable 4x4 and there has been a lot of de­bate around the use of all-wheel drive on wet tar roads for safety rea­sons. Is there any harm in selecting 4H on a wet, tarred road? I un­der­stand that 4L locks the cen­tral diff? If so, then surely it is not ad­vis­able? IAN SHAW Dur­ban

It all de­pends on the type of 4x4 sys­tem that is fit­ted to your ve­hi­cle (please see our tech­ni­cal fea­ture on page 96 ex­plain­ing the sub­ject and also re­fer to your owner’s man­ual). We asked off-road guru and mul­ti­ple rac­ing cham­pion, Hannes Grob­ler – now at 4x4 Mega World Zambesi – for fur­ther ad­vice:

“A dif­fer­en­tial on an axle (or trans­fer case) takes care of the speed dif­fer­ence be­tween the wheels on an axle (or front and rear axles)

dur­ing cor­ner­ing. When driv­ing in 4x4 mode, there must be a mech­a­nism be­tween the drive to the front and rear axles to take up the speed dif­fer­ences be­tween the axles on high-fric­tion sur­faces such as tar (even when wet). A dif­fer­en­tial is the ob­vi­ous so­lu­tion, but many part-time 4x4 ve­hi­cles also use vis­cous cou­plings or multi-plate clutches to en­gage the non-driven axles (nor­mally rear) when slip is de­tected on the driven wheels (usu­ally front). Many bakkies (nor­mally rear-wheel drive) with a selectable trans­fer case have no cen­tre dif­fer­en­tial, as in the case of the Hilux, but in­stead lock the drive 50:50 be­tween the front and rear axles when en­gaged. In these sys­tems, it is not ad­vis­able to se­lect 4x4 on high-fric­tion sur­faces be­cause it can lead the driv­e­train to wind up and get dam­aged.”

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