UAEOffroaders

Hey, guys -

Not long ago, a very experienced (and very mechanically-minded) offroading mate was having trouble with the gearbox (4-high) in his manual sherookee. He has gotten the problem fixed by now, but it took him a while to get the work done. In the interim, one day when he was out in the desert, he tried driving the car in 4-low, using gears 4 and 5. He was impressed with the results (great torque, low revs) and suggested I try it.

I have tried it, and it's a bit weird, but it I'm intrigued. My question is this: What's the downside of driving like this? (There must be one... no??) Extra wear/tear on the engine?? Even if the revs are lower than when I drive in 4-high??

What problems might be caused?

Well. with respect to my jeep, i use mainly gears 3,4, and 5 when i low gear as the wrangler revs too high and gears too short in lower gears (1 , and 2). The only downside is that you should learn which gears to stick to when you need certain power coz being in higher gears, you could lose power fast when climbing,...... in a higher gear. from my knowledge, driving at lower rpms you are actually relieving the engine. The only difference is amount of power. The wear and tear should be the same if used properly in both high and 4-low.

Saleh - just to be sure I get you: do you use 4-low (gears 3-4-5) all the time when you're offroading, or only when you're in a sticky situation?

I would first use 4 high (first choice) if terrain is very easy and smooth. If i feel that there will be quite a lot of climbing, sliding and soft areas, i tend to use 4low for the duration of the trip because with 4high on my jeep i will mostly be using and having to down shift/upshift between 1 and 2. and in some tight cases, gear 1 in 4high isnt enough. but based on the terrain during the trip i will use 4low for a whole trip. I do though shift back up to 4 high when i know we are going to travel quite some distance on smooth terrain to relive the car a bit .

The only difference between HI and LO is the size of the gear, so mechanically there is no more or less wear, nor any downside.

The issue can be that since the gears run shorter in LO (the revs fly up faster) some drivers tend to redline too much.

See the middle gear in the diagram below, the one labelled "Idler Gear"? That's the difference between HI and LO...
In this diagram the "Idler Gear" is in HI, and with the transfer case lever you move it to the left to engage LO.

I think that has made it very clear.. I did have this argument a few times.. but the diagram has explained it very well.. Thank you PR.

With the inline6 4L jeep engine, the trick for maximum torque is to keep the revs at about 3000 or so - certainly no lower than 2500 because the torque really drops off at those lower revs. In my automatic GC that means "2" most of the time, dropping down to "1" when the speed tails off. However, the torque also tails off above 4500 revs so really 2500-4500 is the sweet spot.

One of the problems with using LOW range on mine is that it's very low geared and that easily send the revs up way too high and limits my speed. That can make it difficult to maintain momentum, especially when climbing slopes. Whilst it does give you plenty of torque at low speeds, it's also hard on the engine, transmission and transfer box if you're trying to move along at a higher speed. It also sounds strained and when it comes to cars if it sounds like you're straining something, you ARE straining something.

Because the torque is all being passed through the reduction gears in the transfer box (AKA transfer case) then for a given vehicle speed you have a higher input shaft speed. That higher input shaft speed creates additional heat in the box and that could lead to over heating and potential damage to internal components such as the viscous coupling on the models with Full Time 4WD, a part which will cost AED 5000 to replace. The transfer box does not have a cooler and only contains about 1L of ATF (automatic transmission fluid) and it would be very easy to overheat it.

Check the owners handbook - jeep themselves suggest a maximum speed for using LOW range for this very reason.

Thanks jane for the question and thanks everyy one for the great info

Naw jane witch gear aree you going to use

Just to say, I was driving my Lexus on low gear every time I go offroading,, and I did that for almost two years and didn't face any issue with the gear.

But when I got the land cruiser I didn't need to use the low gear because its manual, except sometimes when its hard terrain.

Like it has been pointed out there is no real harm in driving in 4 Lo provided you maintain the revs at lower levels. The down side that I experienced is that you will burn more fuel.

Keep the 4L for sticky situations or for steep climbs that require more torque and coming down a steeep dune.

4H is the ideal option for desert driving.

I usually drive in 2H and shift to 4H on the fly as required.