Many Denver drivers choose four wheel drive or all wheel drive for good reason. Snowy mornings, steep mountain roads and quick changes in weather make extra traction appealing. But a 4WD or AWD system is only as good as its condition. The parts that send power to all four wheels sit out of sight, work hard in tough conditions and can go for long stretches without attention. Then the first big storm arrives and you find out whether they are ready. Fall is the right time to look them over. This guide explains what 4WD and AWD systems need before snow season, the signs of trouble, the role of tires and what you can expect from service. If you are searching for 4WD service in Denver, here is a practical overview.
4WD vs. AWD: A Quick Difference
The two terms are often used loosely, and the details vary by vehicle, so your owner’s manual is the best guide to how yours works. In general:
- AWD systems usually operate automatically. The vehicle sends power to the wheels that need it, often without any input from you.
- 4WD systems are common on trucks and larger SUVs. Many let the driver choose between two wheel drive and four wheel drive modes, and some offer low range gearing for severe conditions. Some are part time systems that should only be used in four wheel drive on slippery surfaces.
Both systems depend on a similar set of parts that need regular care. Knowing which one you have, and what your manual says about when and how to use it, is the starting point for everything else.
What Is in the Drivetrain
Power travels from the engine through the transmission and then to the wheels through a chain of components. In a 4WD or AWD vehicle, that chain includes extra parts that a two wheel drive car does not have.
- The transfer case on many 4WD vehicles splits power between the front and rear axles. It contains gears or a chain and uses its own fluid.
- A power transfer unit or center coupling on many AWD vehicles does a similar job.
- Front and rear differentials let the wheels turn at different speeds in turns, and they have their own fluid too.
- Driveshafts and axles, including universal joints and constant velocity joints and their protective boots.
- Actuators, sensors and controls that engage the system and manage how power is sent.
Each of these parts works under heavy loads, especially in snow, mud and on steep terrain, and each depends on clean fluid and healthy seals.
What to Service Before the Snow Arrives
Drivetrain fluids
Transfer case fluid, differential fluid and transmission fluid all do important work. They lubricate gears and bearings, carry heat away and protect surfaces. Over time they break down and collect fine metal particles. The right fluid type and the right service interval vary by vehicle, so check your owner’s manual and do not guess. A technician can inspect the fluid for color, smell and debris, which can reveal wear before it becomes a failure. Using the wrong fluid can damage the system, particularly in AWD vehicles that rely on specific fluid properties.
Tires
Tires are the most important part of any winter setup, and they matter even more with 4WD and AWD. Many drivetrains are sensitive to differences in tire size or wear between the four tires. Mismatched tires can strain parts like differentials and couplings. Your owner’s manual may list guidance about tire size, matching and rotation, and following it helps protect the drivetrain. Check:
- Tread depth and even wear across all four tires.
- Tire pressure, using the sticker in the driver’s door jamb or your owner’s manual.
- Whether the tires are suited to winter conditions.
- Signs of damage such as cuts, bulges or cracks.
- Whether rotation and alignment are due.
Axles, joints and boots
Cracked or torn rubber boots on constant velocity joints let grease escape and dirt get in, which can ruin the joint. Look for grease flung around the inside of the wheel or under the car. Clicking when turning, or vibration at speed, can mean a worn joint or driveshaft part.
Seals and leaks
Seals around the transfer case, differentials and axles can leak as they age. Spots under the vehicle or wetness on those parts are worth checking. Low fluid can lead quickly to damage, so do not let a leak go.
Engagement test
If your vehicle has a selectable 4WD system, test it before you need it. Follow your owner’s manual for how and when to shift. Make sure it engages and disengages smoothly, that the indicator lights work and that you do not hear grinding or feel binding. A system that has not been used all summer can stick.
Brakes
Four wheel drive helps you get going, but it does not help you stop. On snow and ice, brakes and tires do the stopping. Have the pads, rotors, brake fluid and lines inspected before winter. Our post on how Denver’s altitude and snow combine to wear down your car covers more of what the region’s conditions do to a vehicle.
Battery and charging system
Cold weather asks more of the battery. Have it tested, especially if it is older, since a weak one can leave you stuck in the worst conditions.
Cooling system and fluids
Make sure the coolant is in good shape and at the right level, and check other fluids such as engine oil and washer fluid using winter appropriate fluid.
Wipers, lights and defroster
Visibility is part of winter readiness. Replace worn wiper blades, check all the lights and make sure the defroster works.
Warning Signs of Drivetrain Trouble
- Whining, humming, grinding or clunking noises that change with speed or when turning.
- Vibration that increases with speed.
- Binding or hopping in tight turns, especially on dry pavement.
- Difficulty shifting into or out of 4WD, or a system that will not engage.
- Warning lights, including a 4WD, AWD, traction or check engine light. Your owner’s manual explains what each light means.
- Leaks or fluid spots under the vehicle.
- Burning smells or unusual heat after driving.
- Uneven tire wear, which can point to alignment or drivetrain issues.
Do not ignore these signs. Drivetrain damage tends to build, and a small problem can become a larger repair if it is left alone.
Using 4WD and AWD Correctly
- Read your owner’s manual. Different systems have different rules, and some part time 4WD systems should not be used on dry pavement because they can bind.
- Do not rely on the system to stop the car. Slow down, leave more following distance and brake gently on slippery roads.
- Match your tires, and replace them as a set or follow your manual’s guidance.
- Avoid spinning the wheels needlessly. It can overheat and wear parts.
- Do not exceed the vehicle’s limits. Towing and loads have limits listed in the manual.
- Carry winter supplies, such as a blanket, a flashlight, a shovel and water, in case you get stuck.
Heading Into the Mountains
If your plans include winter drives in the mountains, you will want your vehicle in top shape before you go. Steep grades and cold conditions put extra demand on the whole drivetrain. Our mountain road trip car checklist lists other items to check before you leave town.
How a Mobile Mechanic Can Help
A mobile mechanic can come to your home or workplace and inspect the drivetrain, check fluid levels and condition, look for leaks and damaged boots, test the battery, look at tires and brakes and tell you what needs attention. Some fluid services may be done on site, depending on the vehicle and how the fill and drain points are reached. Other work, such as replacing axles, seals, transfer case parts or other major drivetrain components, may need a lift and specialized equipment and may be better handled at a shop. A good technician will be upfront about what can be done where you are.
Quick Pre Snow Checklist
- Review your owner’s manual for the 4WD or AWD system.
- Check transfer case, differential and transmission fluids.
- Inspect axles, boots and joints.
- Look for leaks.
- Test 4WD engagement if your vehicle has it.
- Check tire tread, pressure, matching and rotation.
- Inspect the brakes.
- Test the battery.
- Check wipers, lights and the defroster.
- Pack winter supplies.
Getting your vehicle ready before the first storm is far easier than dealing with a problem on the side of a snowy road. If you would like help, visit the Mobile Mechanic Pros of Denver homepage to learn more, or contact us to schedule a visit.
