Four Wheel Drive Service: What’s involved?

Learn What Happens During a Four Wheel Drive Service

As someone who’s been around four-wheel-drive (4WD) systems for years, I can tell you this: neglecting your four-wheel-drive service is a surefire way to invite trouble. A 4WD vehicle is built for rugged terrain and adverse conditions, but like any complex system, it needs routine maintenance to keep it performing at its best. If you think you can skip the recommended four wheel drive service milestones, you’re setting yourself up for costly repairs down the road. Let me break down exactly what happens during a four-wheel drive service and why each step matters.

Step 1: Inspecting and Servicing the Transfer Case

The transfer case is the heart of your 4WD system. The transfer case receives power from the engine and distributes it to the front and rear differentials and the axles. During a four-wheel drive service, I always start with the transfer case. The fluid inside it acts as both a lubricant and a coolant, reducing friction and heat. Over time, this fluid breaks down, losing its ability to protect the internal components.

The shift motor moves the shift fork to change from 4-Lo to 4-High gear ratios.

I start by checking for signs of input/output seal leakage. If I see signs of seal leakage, I replace them to avoid the potential damage that can occur if the fluid levels inside the transfer case drop to dangerous levels.

Nest, I drain the old fluid, inspect it for signs of metal shavings or contamination, and refill it with the manufacturer-recommended type of fluid. This isn’t the time to cut corners—using the wrong fluid or a “universal” fluid can lead to poor lubrication, overheating, and even catastrophic failure of the transfer case.

Step 2: Servicing the Differentials

Your vehicle’s front and rear differentials are responsible for distributing power to the wheels. These components are filled with gear oil, which keeps the gears lubricated and prevents metal-on-metal contact. But gear oil doesn’t last forever—it degrades over time, especially if you’ve been towing, driving off-road, or exposing your vehicle to water crossings.

Most differentials have a drain plug and a fill plug. However, this particular differential didn’t have either. So, we had to remove the differential cover to drain the fluid.

During a four-wheel drive service, I’ll drain and replace the gear oil in both differentials. I also check for leaks, inspect the seals, and look for metal particles in the old oil—these can indicate internal wear that might require further attention.

Step 3: Examining the Driveshaft and U-Joints

The driveshaft and universal joints (U-joints) transfer power from the transmission to the axles. These components are often overlooked, but let me tell you, neglecting them is a big mistake. A failing U-joint can lead to vibrations, clunking noises, or even a complete loss of power to the wheels.

The U-joint consists of a cross and four bearing cups. Each bearing cup is lined with needle bearings and is filled with grease. Notice the rubber seal on the bearing cup. The seal keeps water out. When it fails, water gets into a bearing cup, washes out the grease, and leaves the bearings without any lubrication. At that point, the bearings start to wear out the cross. Notice the wear on each section of the cross. This created severe vibration in the drive shaft.

During a four-wheel drive service, I inspect the driveshaft for dents or damage and check the U-joints for excessive play or wear. If your U-joints are greasable, this is when I’ll lubricate them. If they’re sealed and worn out, I’ll recommend replacing them to avoid potential breakdowns.

Step 4: Testing the 4WD Engagement System

Modern 4WD vehicles often have electronic or vacuum-operated systems to engage the front axle or transfer case. These systems can fail due to electrical issues, vacuum leaks, or actuator problems.

Part of a thorough four-wheel drive service includes testing the engagement system to ensure it’s functioning correctly. I’ll manually engage and disengage the 4WD mode, listening for unusual noises and feeling for smooth operation. If there’s an issue, it’s far better to catch it in the shop than to discover it when you’re stuck in the mud or snow.

Step 5: Inspecting the Suspension and Tires

Your 4WD system works hand-in-hand with your suspension and tires. During the service, I always check the suspension components, including bushings, control arms, and shocks, for wear or damage. Your tires also need attention—uneven wear patterns could indicate alignment issues or problems with the 4WD system itself.

Rotating the tires and balancing them is often part of the service, as it ensures even wear and maintains stability. Remember, your 4WD system is only as good as the traction provided by your tires.

Step 6: Lubricating Key Components

Finally, I take the time to lubricate all greaseable components, including the steering linkage, ball joints, and any other moving parts in the drivetrain. Proper lubrication minimizes friction, reduces wear, and extends the life of your vehicle’s critical components.
When to Schedule Your Four-Wheel Drive Service

How often you need a four-wheel drive service depends on how and where you drive. For most people, servicing every 30,000 miles is a good rule of thumb. However, if you frequently tow heavy loads, drive off-road, or encounter water crossings, you should consider more frequent maintenance. Check your owner’s manual for specific recommendations, and don’t ignore warning signs like strange noises, difficulty engaging 4WD, or leaks.
Final Thoughts

As someone who’s serviced countless 4WD systems, I can’t stress enough how important regular maintenance is. A well-maintained four-wheel-drive system will provide reliable performance, whether you’re tackling tough trails, navigating icy roads, or just cruising around town. But skip a four-wheel drive service, and you’re gambling with expensive repairs that could have been avoided.

So, don’t wait until you’re stuck in a bad situation. Schedule your four-wheel drive service today, and keep your vehicle ready for whatever the road—or the trail—throws your way.

©, 2024 Rick Muscoplat