Switching from 4hi to 4lo while driving at higher speeds is not recommended at all. But some manufacturers indicated that switching from 4hi to 4lo is safe at crawling speeds (like 1 – 3 mph) or after stopping.  

In this article I’ll talk about why it’s not safe to shift from 4hi to 4low while driving and precautions to take when switching from 2wd to 4wd while driving at high speeds.

For the better understanding I’ll first discuss briefly how the four wheel drive system works and then talk about the main questions.  

Finally I’ll show you a few better modifications done to 4wd drive systems by vehicle manufacturers for the sake of feasibility of drivers.

Simple explanation on 4wd systems

Mainly there are part time and full time four wheel systems.

The part time 4wd system generally consists of the engine, transmission unit, transfer case and front and rear propeller shafts. 

Full time 4wd systems don’t have a transfer case. There’s a center differential and a diff lock.

I had explained those things in depth in previous article. You can check it by clicking here.

As you know part time 4wd systems have 4 hi and 4 low ranges. 4hi range gives less torque and hi speed crawling.

It’s best for normal off-roading activities.   

4low range gives hi torque in low speeds (less than 10 mph).

Low range is only used for extremely challenging rock crawlings, towing and mud crawlings like high power, low speed and more control needed instances. 

Here I gave you a brief explanation about general things about the 4wd drive system because I had explained them in previous posts. Check them for more depth details. 

Is switching to 4wd while driving safe? 

Actually this depends on the vehicle. Most of the new part time 4wd drive vehicles can shift to 4wd mode from 2wd mode safely while driving. (Normally called this as “shift on the fly”)  

The maximum safe speed and the safe procedures for shifting to 4H could be found in vehicles users manual. So refer to it.

Normally below 60mph is safe on those kinds of vehicles. 

But in old vehicles normally you can’t shift to 4wd mode without stopping the vehicle.

In those vehicles you have to stop the vehicle and manually lock the hubs getting down the vehicle.  

After that you have to shift to the 4wd mode and start to ride. I have talked about hub locks in another article. Read that also for better understanding.  

It’s not safe to shift to 4wd mode while driving on those old vehicles. You will end up causing damages to your transmission system and other mechanical parts.   

It’s best to check your vehicle’s manual before attempting to do this if you have a much older vehicle.

Because this differs from vehicle to vehicle.

Is switching from 4hi to 4low while driving is safe ? 

Normally this is not safe. 4lo means it has low gear ratios. It’s best to maneuver less than 10mph speeds.

So if you try to shift from 4hi to 4lo while driving at higher speeds, exactly it will cause damages to your vehicle.

So that most of the modern manufacturers avoid this by various mechanisms.   

To shift  4lo you have to completely stop your vehicle and then you have to put in that gear or you have to slow the vehicle to a crawling speed (like 1 – 3 mph) and shift to the 4lo after putting the vehicles transmission in to neutral.  

Most of the vehicles don’t allow to change from 4H to 4L without putting the transmission in to neutral position.

New modifications done by various manufacturers to the 4wd drive systems 

Jeep wrangler 4A mode

Jeep Wrangler has 2H – 4H – 4A – 4L in it’s transmission. This 4A is auto mode of 4wd.

It means when 4A selected jeep 4wd system automatically adapt to the road conditions and do its job reducing drivers active involvement.  

It can automatically shift between 4hi, 4lo and 2h according to road condition.  

It will exactly reduce binding of 4wd systems like harmful instances. So it can leave active in high traction surfaces without any problem.

It will act like a AWD system on those surfaces.  

So far I think you got the understanding of why is it harmful for switching from 4hi to 4low while driving.   

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Have fun and safe off-roading !!