You’ve probably seen 4×4 vehicles roaming the streets and heard of them conquering the great outdoors.
Aside from having that extra power and improved traction, 4×4 vehicles are also designed with all-terrain flexibility and impressive towing power, making them the ideal off-roading companion.
Some vehicles have all-wheel drive, which means all four wheels are always driving the vehicle. This provides tremendous stability not available to 2-wheel-drive vehicles, regardless of the type of road surface or weather.
4×4 vehicles have these advantages because they come with a four-wheel drive (4WD) system.
What’s a 4-Wheel Drive Vehicle?
A vehicle with a four-wheel drive system has two differentials that let the front and rear wheels travel at certain distances and speeds while cornering or driving over bumps.
On a four-wheel-drive vehicle, all four wheels must be exactly the same size (making regular tire rotation that much more important, coupled with the fact that all four tires should always be replaced every time tires are purchased). The ring gear and pinion assemblies must also have exactly the same gear ratio.
Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.
Pro Tip: Different size tires on the front and rear or trying to operate in four-wheel-drive on hard pavement will cause driveline windup. This will destroy the transfer case, which is the part of the drivetrain that splits the power between the front and rear axle assemblies when in four-wheel-drive mode.
When Should You Use 4WD?
Heavy-duty jobs like hauling or towing are best suited for four-wheel driving. But again, four wheel drive should never be used on hard pavement unless the vehicle has a mode designated as “full-time 4WD.”
Rugged terrain, off-road trails, snow-filled streets, and muddy roads are conditions where using part time 4WD is appropriate. However, vehicles equipped with part time-only 4WD shouldn’t be driven in four wheel drive on regular roads.
How to Use 4WD
4WD systems usually have three positions in their transfer case that let the driver select a gear ratio. Here’s how each one works.
4WD High
There’s no gear reduction in 4WD high. It’s used on slippery surfaces or when driving in snow, mud, or ice.
4WD Low
Using 4WD low restricts the vehicle to low speeds on slippery surfaces. On automatic transmissions, the transmission shift strategy will be different, in that shifts will happen a lot earlier and top gear will be achieved at a very low speed due to the engine’s power curve in four-wheel-drive low range. It’s ideal for towing under low speeds and when negotiating steep grades.
On automatic transmissions, the transmission shift strategy will be different, in that shifts will happen a lot earlier and top gear will be achieved at a very low speed due to the engine’s power curve in four-wheel-drive low range.
–Richard McCuistian, ASE Certified Master Automobile Technician
2H
This mode puts the vehicle in two-wheel drive mode, which usually powers the rear drive wheels. There’s no gear reduction in the transfer case under this mode.
Keep in mind that not all 4×4 vehicles are capable of shifting to 4WD when in motion. Exceptions would be automatic four-wheel-drive systems that engage whenever one of the rear wheels are spinning, as well as “shift on the fly” systems that have a button on the dash and a magnetic clutch built into the transfer case specifically for selecting four-wheel–drive without stopping the vehicle.
4WD systems where four-wheel-drive is selected with a lever rather than a button require the driver to stop the vehicle completely and put the transmission in park or neutral.
Sophisticated 4WD systems automatically shift in and out of four-wheel driving, depending on the amount of traction the vehicle needs.
4WD Maintenance
Owning a 4×4 requires more maintenance tasks than your average vehicle. You’ll need to keep an eye out for potential issues that could develop in the transfer case and differential.
Like most engine components, the transfer case needs fluid to keep everything running smoothly. The problem with transfer case oil leaks is that there’s no low oil indicator on most transfer cases. A transfer case that has lost its oil (even through a slow leak), will destroy itself in short order, so you need to have the transfer case checked for leaks (or check it yourself) whenever the oil is changed.
Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.
Pro Tip: If the transfer case is leaking from between the case halves rather than a seal, the transfer case will need to be disassembled and resealed.
Depending on how often you use 4WD, you might need to replace the transfer case fluid once every 50,000 miles and the differential fluid between 30,000 and 60,000 miles. That being said, OEMs don’t typically call for changing either of these fluids if there are no issues with the respective units.
You should also use the 4WD system regularly. Leaving it unused for months can cause the hub and linkages to seize and the seals to dry out. Note, however, that this isn’t always the case.
Common Problems with 4WD Systems
4×4 vehicles are built to handle the toughest road conditions out there, but they’re not exactly bulletproof. Here are some of the most common problems you might encounter while driving a vehicle with a 4WD system.
Worn-Out Shocks
This isn’t a four-wheel-drive problem per se, but four-wheel-drive vehicles that are often driven on rough terrain will typically wear the shock absorbers out sooner.
Shock absorbers dampen and control the movement of the springs, preventing the vehicle from bouncing up and down after hitting bumps. Shocks essentially control handling, while the springs support the weight of the vehicle.
Your vehicle’s suspension system absorbs most of the impact when driving on rough terrain, which also causes the shocks to wear out faster than normal.
After some time, you might notice that your rides are getting bumpier than the last one because the shocks can’t absorb impact anymore.
Damaged or Worn Transfer Case
The transfer case uses the driveshaft to transfer power from the transmission to the axles. In the case of a 4×4, the transfer case lets the driver select an appropriate gear ratio, depending on the road condition.
Regular wear and tear, low fluid levels due to leaks, and poor maintenance are some of the reasons why a transfer case can fail.
Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.
Pro Tip: Most transfer cases use a large chain that tends to stretch, and it can wear the transfer case housing to the point that the housing is breached. There are kits you can buy that include a new chain, new seals, and a replacement case half, but you’ll need to know which transfer case you have to get the right parts.
Malfunctioning 4WD Feature
You might notice a warning light on your dashboard indicating that the 4WD system isn’t working as it should. In most cases, an overheated transfer case, sensor failure, and incomplete gearshift are the culprit.
Once this happens, you will typically still be able to drive in 2WD mode. However, it’s best to have your vehicle inspected by a trusted professional, especially if you’re planning on doing any off-roading.
Cracked Chassis
Driving on rough terrain will most likely cause your chassis to crack. While small cracks might not seem like a major issue, they can let moisture in and accelerate the rusting process. Note that this can also happen if you’re driving a two-wheel-drive vehicle.
Speed Variation Techniques in 4WD Systems
Three methods make front-to-rear driveline speed variation possible: locking hubs, auto locking hubs, and full-time four-wheel drive. All-wheel-drive vehicles have a viscous coupling built into the four-wheel-drive system that will, by design, still transmit torque while allowing different speeds for the front and rear propeller shafts.
Locking Hubs
As the transfer case powers the differential, torque is also applied to the drive axles and locking hubs. If the vehicle is using 4WD high, the front hubs must be unlocked. Front hubs are locked only when the vehicle is driven on loose road surfaces.
Some four-wheel-drive vehicles have outer and inner shafts, with the outer shaft always locked to the wheel and the inner shaft always driven by the transfer case when four wheel drive is engaged. The outer and inner shafts have splined ends and a moveable sleeve that connects the two shafts automatically when four wheel drive is selected.
Auto Locking Hubs
The hubs connecting the front drive wheels to the front differential will automatically lock as soon as a great difference in speed is detected from the front and rear wheels. The system described in the previous paragraph, is automatic but locks the outer drive axle to the inner drive axle rather than simply locking the hub.
Full-Time Four-Wheel Drive
This method uses a center differential with a viscous coupling so that the front and rear wheels can travel at different speeds under all operating conditions.
Where to Get Replacement Parts for Your 4×4 Vehicle
Your 4/x4 vehicle is designed to handle rough terrains. But like any other vehicle, its parts can wear out over time. If you’re on the lookout for new replacement parts for your 4×4, look no further than CarParts.com.
We have a wide selection of vital components like shocks and transfer cases sold at unbeatable prices. Simply input your ride’s make, model, and year into our easy-to-use vehicle selector. You can also filter your options according to the price range or brand you prefer.
Explore our comprehensive selection of 4×4 parts. Each product has been screened to ensure it delivers excellent reliability and performance. Contact us on our toll-free hotlines if you need help checking for fitment or if you have any other questions about your order.
Worried about extended shipping times? We have multiple warehouses across the country to ensure your orders will reach you in a matter of days.
Keep your 4×4 running at its best. Get faulty components replaced right away, so you can plan your next off-road adventure soon!
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