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Go Back   Hummer Forums by Elcova > General Hummer Talk > Off-Roading

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Old 11-14-2007, 04:43 AM
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Default Knowing your H2's 4WD System


So there you are, heading down the trail for the first time and you have all these mysterious buttons in front of you to control your 4WD system, which ones do you need to push?
First and foremost, we should not forget one of the old off road clich?s, "Drive as slow as possible, but as fast as necessary". There are times, sand, mud, etc, when you need to keep up a certain momentum to keep you going, however, it is generally accepted practice to tackle a trail as slow as possible. This not only allows you to see what is coming, pick the right line, and adapt to changing conditions, but it will also minimize the possibility of breaking something. So with that mind, unless absolutely required, a gentle and steady foot on the gas is needed at all times.
So what do the buttons do and which one should you use? As with all things, experience will teach you what settings are appropriate for the terrain you are tackling, but are some basic pointers we can use.
Traction Control System
The H2 utilizes a Traction Control System that controls wheel spin. Generally this is a good thing, but there are times when you want the wheels to spin, for example when in mud you want to spin the wheels to spin the mud out from between the lugs, you may also want to spin a wheel or two on sand, so that the other gripping wheels can maintain momentum. Fortunately, the TCS system comes with another setting, TC2, that will allow a little more wheel spin. TC2 only works in 4HI Lock and 4LO Lock, and will not work in the normal 4HI transfer case setting.
Low Gear Selection
When in deep mud or loose sand a lower gear setting is also advantageous, higher RPM's allow the wheels to keep moving freely and prevent the vehicle wheels "sticking". When descending steep hills, you should also select 1st gear, this will allow the engine to take over some or all of the braking requirement, preventing potential skids when applying the brakes.
Transfer Case Use
Depending on the trail and the severity of the obstacles you will be tackling, 4HI Lock or 4LO Lock is generally recommended. You can shift between 4HI and 4HI Lock at any time you are travelling less than 40 mph, however, it is advisable to select the correct transfer case setting before you need it, and avoid switching between 4HI and 4HI Lock if your wheels are spinning. You need to be in Neutral to shift into 4LO Lock and the vehicle must be doing less than 2 mph, ideally you should be rolling at 1 or 2 mph with the transmission in Neutral when switching in or out of 4LO Lock. When in 4LO Lock you can also lock the rear axle, which again requires the vehicle to be stopped or moving at less than 2 mph, sometimes you may have to roll forward a few feet at 1 or 2 mph for the rear axle lock to engage.
4HI Lock or 4LO Lock
Okay, so now we know how to use the buttons, but which ones do we select on the trail? 4HI Lock will give you extra traction on the trail and is most probably the most common setting. If the trail is muddy, or on sand, then selecting TC2 at the same time will be advantageous. Tackling more serious obstacles, steep hills (up and down), loose sand, deep mud, etc, will be best achieved in 4LO Lock. This will not only deliver maximum power to the wheels, but will also change the throttle control to be less sensitive, thus giving you better control over the vehicle and reducing the risk of accident.
Rear Axle Lock
When you have one of the rear wheels in the air, or are not able to gain traction with one of them, all the power will be transferred to the wheel with no traction. Obviously, this prevents you from effectively applying any power at the rear and you are now solely relying on your front wheels to move the vehicle. By locking the rear axle, (essentially physically locking the two rear wheels together), the power goes to both rear wheels regardless if one cannot gain traction. Therefore, you will still be using the wheel with good traction to move the vehicle forward. Locking the rear will also keep power distribution uniform at the rear of the vehicle, minimizing slipping and sliding.
If the terrain is very uneven where you are may be lifting a rear wheel off the ground, then you may want to lock the rear axle. Likewise, locking the rear axle when tackling steep obstacles, uneven inclines, very loose sand and deep mud, will reduce the potential for getting stuck and keep both rear wheels moving. If you spin the wheels a lot with the rear axle locked, you may notice that the axle unlocks itself, this is to protect the axle and quite normal.
It is worth mentioning again, that when axles and diffs are locked, the potential for damage increases with speed or heavy throtle use. Drive slowly, and let the torque of the H2 work for you. You will see people deliberately spinning wheels on rocks and other terrain, sometimes to dry the tires out, other times to manhandle their way over a particularly difficult obstacle. This should only be attempted, if a/ you know what you are doing, and b/ you understand the potential risks involved.
Brake Throttle Modulation
One other technique that is very useful when tackling obstacles, is Brake Throttle Modulation (BTM), a variation of the old Left Foot Braking used by rally and other racing drivers. BTM primarily does two things, it acts in a similar way to a locker, something that the stock H2 lacks at the front, and it also allows for more controlled progress over obstacles. To use BTM, bring the vehicle to a stop, apply the brake with your left foot, slowly bring up the RPM's (no more than 2000 RPM) and slowly release the brake with your left foot, modulate between the two if necessary, maintaining a slow but steady pace. This will prevent wheels with little traction spinning and transfer maximum torque to the wheels with traction, it will also prevent any sudden movement forward.
Picture this, you are crossing a large log, at an angle so that one wheel at time goes over the log, as each wheel comes down the log gravity will take over and want to pull the vehicle down and forward suddenly. By using BTM you will prevent this from happening and make slow steady progress over the log. The same principles apply when tackling uneven rocky terrain, deep ditches, walls, sheer drops, etc.
Another application of BTM is when on a slippy or loose surface where momentum cannot be maintained, either due to potential hazards or a slow entry point. By applying BTM techniques you are partially recreating the same result as using a locker. The wheels with less traction are less likely to spin, as the brakes are holding them, allowing power to still be applied to the other wheels with traction. Good results can also be achieved using BTM when you have one of your front wheels in the air, BTM will allow some power to still be transmitted to the wheel on the ground. Obviously, special attention should be made not to suddenly release the brake when using BTM.
Another added benefit of BTM is that it deactivates TCS/TC2.
Ride Height Control
If your vehicle is fitted with Ride Height Control this can be used to raise the rear of your vehicle approximately 2". This will increase your break over angle, departure angle and generally give you more underbody clearance, all useful benefits when on the trail. Due to the increase in center of gravity, you may not wish to use this feature on steep side slopes, unless dictated by the nature of the terrain.
The above is not meant to be an in-depth look at the H2 4WD system, but covers the basics. With this knowledge and some trail experience, you will rapidly learn to know which particular settings should be used for the terrain and obstacles you will be tackling. Despite the incredibly efficient H2 4WD system there will be times when you get stuck, you should have a good undertsanding of how to recover the vehicle in such event. Click here for info on basic recovery techniques.
Although it's been said more than once, it is worth repeating one more time, "Drive as slow as possible, but as fast as necessary".
I'm touching myself thinking about yellow people.

Last edited by Walter_Cronkite : 11-14-2007 at 04:53 AM.
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Old 03-12-2008, 05:20 PM
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Default Re: Knowing your H2's 4WD System

This is all very nice. What about a sticky guide to the H3 4WD System!
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