Winter Roads

All About Transfer Cases

Those who are looking to get the most out of their offroad experience should learn about the components of their vehicle, so they can know which parts will benefit them most to upgrade and maintain. It’s a good idea for any offroad enthusiast to know the in and outs of the auto parts that run their vehicle, and one of the most important components to a proper 4×4 is the transfer case. The transfer case is one of the most important pieces to operating the 4 wheel drive system, and this article will give a description as to how it works in a 4×4 vehicle, and why it is an important component to making an offroad vehicle work properly.

A transfer case is a motorized component that directs power to both axels through two drive shafts, allowing power to be delivered to all four wheels, effectively creating a 4×4 vehicle. 2 wheel drive vehicles don’t need a transfer case, because the power is delivered from the transmission directly to one drive shaft, therefore their drive systems are much more simple. The transfer case is attached to the rear of the transmission and receives its power from the transmission. Power gets directed from the engine, to the transmission and then to the transfer case.

Within the transfer case are a series of gears or chains that allow the user to switch between different gear ranges, low range and high range depending on how much power is needed. This also happens to be one of the main differences between 4 wheel drive and all wheel drive. In a 4 wheel drive vehicle, the driver can switch between different torque modes/gear ratios, which is ideal for offroad and rock crawling, and all wheel drive systems have one gear ratio. If the 4-Hi mode is selected, the front driveshaft is engaged inside the transfer case and power is distributed between the front and rear driveshaft, allowing all four wheels to have power. 4-Hi is a good setting to use when you’re experiencing light terrain, or have mild challenges to climb. Off road trails with loose gravel, light sand, light mud and small boulders is good terrain to engage 4-Hi. 4-Lo is appropriate when the trail is very muddy, there are large boulders to crawl, or when you are ascending or descending a very steep hill. The 4-Lo gear ratio uses as different gear allowing power to directed the rear and front axel, allowing more torque for steeper hills or large obstacles. Most transfer-cases in true 4×4 vehicles will have a high range ratio of around 1:1 (meaning the input turns one time for every one time the output turns on the gears), and the low ratio will be around 3.5:1 (3.5 input turns for every one output turns).

It’s also beneficial to know about crawl ratios. The “crawl ratio” is a term used to describe the lowest gear you can achieve, and is calculated using the lowest ratio of the transfer case and transmission. By multiplying all of the gear ratios through the entire drivetrain, you will be able to find out your crawl ratio. The lower the crawl ratio, the slower you’ll go, but the more torque you’ll have and easier it will be to go through obstacles. In addition, your vehicle’s tire size has a factor in what crawl ratio is available. Shorter tires will yield a lower crawl ratio than taller tires, and larger tires will yield a higher crawl ratio.

The transfer mode selector in your vehicle describes how your particular vehicle will switch into its various modes. There are two types of transfer case selectors, mechanical and electrical. In most modern vehicles, you can press a button or select a dial and the vehicle’s parts will electronically select a gear ratio. In some vehicles, a lever is engaged which will manually switch between ratios.

For those of you who are extreme offroad enthusiasts, you may consider a double transfer case. When a very low crawl ratio is desired for extreme rock crawling, extensive modifications may be needed for those looking to build up their rig. A double transfer case can be attached in a series, and the gear ratio is doubled, making it significantly easier to crawl up large obstacles. Some super low crawl ratios have even been known to get near 400:1.

A properly maintained transmission, transfer case, and all 4 wheels parts are very important, as they take a lot of abuse from offroad use. To see how much abuse and wear and tear your transfer case has taken, it’s important to regularly visit your 4×4 mechanic.

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