It depends what kind of engaging system you have. With a manual transmission there will be a shifter for engaging your transaxle. It should have the numbers on the knob that say 2H, 4H and 4L. The H letter stands for high. The L letter stands for low. With a four-wheel drive it is okay to shift between 2H and 4H while moving.

But for you to put the transaxle into 4L (four-wheel drive 4 Low gear ratio) means you are changing the gears from the high speed gear ratio part of the transmission to a lower gear ratio, you must completely stop forward or rearward velocity to do this.

If it is a manual transmission, stop the truck completely and shift it into 4L. When you do this you will be in a completely different gear ratio than the 4H. When you take off you should notice a difference in the motor speed and your actual physical speed.

The truck should max out on the r.p.m. gauge much quicker than the 4H side of the transaxle. That takes care of the transaxle part of changing it to four-wheel drive. Now to the lock-out, lock-in part of the procedure.

The front wheels must be locked-in. On older trucks, that means you need to get out of the truck and go to the front left wheel and physically move the lock-out to the lock-in or four-wheel drive position.

It is located in the center of the wheel, and it usually has an arrow that points to in or out and indicates whether or not the wheel is locked-in for the four-wheel drive to work properly. You must do this on the right front wheel as well. You're ready to go.

Some of the newer trucks have a switch or button inside the truck cab, usually located on the dashboard, that will engage your lock-outs, lock-in automatically. If you have that system, you will not have to get out of the truck, at all, to engage your front wheels. That means not having to wade in the mud to engage your lock-outs.

If you have an automatic transmission, it's much simpler to engage the transaxle and the wheel lock-outs. For an automatic to shift from 2h to 4h just change the engage button usually located on the dashboard.

But, to do the 4L part you must come to a complete standstill. I have a Ford Ranger four-wheel drive. I come to a complete halt then shift the transmission into neutral. With the transmission in neutral, with my foot on the brake to make certain the truck does not move, I move the button that changes the gear ratio from the 4H position to the 4L position.

The 4L part of driving is usually used to pull up stumps or climbing steep grades or pulling vehicles that are stuck. The front wheel lockouts are automatic so I don't have to get out of the truck for that part of the operation. You are now ready to drive the truck.

One piece of important advice I recommend is that if you are mudding or on snow and you know your wheels are going to be spinning very easily you should make certain your transaxle is in the 4H position.

That's because in the 4L position you will max your motor r.p.m.s very quickly. The higher motor r.p.m.s combine with the stronger but lower gear ratio and you will need to shift your transmission much, much quicker than you would if it was in 4H four-wheel drive.

So in snow or mud you should mostly keep the transmission in the High part of the gear ratio. If you do this in the Low gear ratios you will need to shift much sooner or you could do serious damage to your truck's motor by over-revving the engine.

I hope this is simple enough for you to understand. You're now ready to go four-wheeling. Have fun. The nice thing about a four-wheel drive is the sense of security that it gives you.

I am disabled and feel much more secure with my four-wheel drive knowing that in most conditions I will be able to go, and don't much have to worry about getting stranded.

Have fun.

Hank Feral
References :
Growing up in the muddy part of the Bootheel in Missouri. Gumbo mud rules!

If not, you have automatic hubs and the truck will lock them automatically. most trucks can shift on the fly to 4×4 high while truck is in motion. Either you have a button to push on dash or a lever to pull to engage. most manuals say do not do this at speeds over 45 mph though. You may have a reminder lamp that says 4×4 while driving.

DO NOT GO INTO 4×4 LOW without coming to a complete stop first! unless you want to pick up pieces of truck behind you. 4×4 low is pulling boat trailers from water, deep mud, plowing, not normal driving! top speed may be 35 mph.

Remember most trucks are not to be driven in 4×4 unless the surface is dirt, grass, snow, ice etc… because trucks are part time systems that need slippage. Otherwise transfer case and other 4×4 parts may wear out faster. (tires too)
References :