thew0rldinside

[thew0rldinside]

4wd To The Rescue

As the owner of a four-wheel drive truck since I was 16, I have seen the great benefits of a four-wheel drive system. I have lived in places such as Idaho where the extra traction saved me from being stuck plenty of times. I also spent a considerable amount of time off-road and have been saved in sand, mud, and water thanks to my four-wheel drive.

In today’s world, car sales are going down every year. More and more people are buying trucks and SUVs. There is even now an national 4WD association https://www.4wdnow.com/! How sweet is that? Many car companies are taking their focus away from sedans, coupes, and compacts and focusing on crossovers, SUVs, and trucks of all sizes. Many of these SUVs and trucks offer a four-wheel drive option or all-wheel drive option. Many people buy these cars with these capabilities and even use them regularly without really understanding how they operate.

The idea of four-wheel drive has been around for a very long time already. The idea hasn’t changed much but modern technology has made it even more convenient than ever. These new four-wheel drive systems are incredibly capable and extremely easy to use. Let’s dive a little further into how these systems work.

Transfer Case

Have you ever wondered what the difference was between four-wheel drive and all-wheel drive? The main difference is that all-wheel drive operates using a center differential and the four-wheel drive uses a transfer case. They both operate using many similar components, but they work very differently. Both of these components are responsible for the sending of power to both the front and rear differentials.

Originally when you wanted to shift your vehicle into four-wheel drive, you had a floor-mounted shift lever that you moved in order to engage four-wheel drive. It was also common for you to have to exit your vehicle and manually lock your hubs. Nowadays, almost all manufacturers use a dash-mounted button to switch to four-wheel drive. When the four-wheel drive button is pressed, it will send a signal to a four-wheel drive control module that will activate an electric motor. This motor moves a shift fork which will engage and disengage the four-wheel drive.

Four-Wheel Drive Technology

One great feature in most four-wheel drive vehicles is called “Auto 4wd”. This essentially allows for the vehicle to operate as four-wheel drive and all-wheel drive. The clutch in your transfer case is what makes this possible. When driving in four-wheel drive mode, more power will be applied to the clutch than in four-wheel drive auto mode. Four-wheel drive auto mode will allow for you to turn sharply without experiencing drive-line bind-up. While you are driving in auto four-wheel drive your vehicle will quickly respond to changing road conditions. This is all possible through wheel speed sensors in each wheel. This system also improves fuel economy as four-wheel drive is only engaged when it is needed.

Below is an excellent video which explains how Jeep’s Selec-Trac 2 system works. You will see a demonstration of how 2wd, 4wd auto, and 4wd low work.

Four-Wheel Drive Ranges

Most modern four-wheel drive vehicles are capable of operating in multiple ranges. The standard range is 2wd drive Hi. This is how you drive your vehicle around normally. Your vehicle will drive as a normal rear-wheel drive. This is helpful to get ideal gas mileage and to prevent excessive driveline strain.

There is also a 4wd Hi range. This will supply power to both the front and rear differentials. In this high range, power will come from the transmission and go straight to the rear output shaft at a 1:1 ratio. The chain in the transfer case will send the same power to the front output shafts since both the top and lower drive sprockets are the same.

You will generally have a 4wd Low option as well. This supplies power to both the front and rear differentials much like the 4wd Hi range does. The main difference is that this uses very low gear ratios in order to send maximum torque and limited speed.

Some vehicles even offer a 2wd drive mode but not many do. This uses the same low gearing as 4wd low but only sends this power to the rear wheels. Many people like this for towing heavy loads. As this mode is very rarely used, it is uncommon to see it in vehicles.

Transfer Case Diagnosis

Now that you’ve learned a little about four-wheel drive systems let’s learn a little about repairing four-wheel drive systems. Your transfer case is the heart of your four-wheel drive. If 4wd isn’t engaging, your transfer case very well could be the culprit. To check to see if your transfer case is engaging or not, lift the vehicle in the air so that all of the tires are off the ground. Then engage four-wheel drive and press the gas. If only one of the drive-shafts rotates then the problem is with the transfer case.

There are really only two things that could be wrong with the transfer case. Either it has a broken electric motor that engages the transfer case or there is a broken/worn component inside of the transfer case.

Listen to your transfer case while someone tries to engage it. If it sounds like it’s trying to engage but isn’t or if you don’t hear anything at all, the problem is likely your electric motor. It very likely could be having electrical issues or have failed. If the system sounds like it is engaging normally but isn’t then it is likely something inside has failed. This could be a worn fork, stripped gears, or worn clutch disks.

Power to All Wheels

Four-wheel drive really is an amazing thing. It allows for amazing things to happen. Four-wheel drive technology continues to improve each and every year. As time goes on four-wheel drive and all-wheel drive systems are starting to blend into one as well. The more you know about your four-wheel drive system, the better you will be able to diagnose and repair it.

If you live in and around the bay area in California, by far the best truck repair mechanics in my experience are the guys at A-1 Auto Tech, Inc.