A differential in a 4WD has several tasks.
One, it directs engine power to the 4X4’s four wheels. Two, it splits this torque to give each of the four wheels varying speed. Further, it’s a gear reduction mechanism that slows the rotational speed of your car’s transmission before this power reaches the wheels.
So, can you drive a 4×4 without a front differential?
Not really, as you need varying speed on the wheels to negotiate turns.
To understand why or how this happens, let’s look at:
How a Differential Works
We mentioned the uses of a differential earlier, and we’ll now go into the details.
Wheels rotate on the axle unit, and there’s a front and rear axle. The differential is on this axle unit, and it enables wheels’ rotation at different speeds. If they don’t turn at different speeds, they screech or damage other components like tires.
As a car turns, there’s a set of wheels on the outside and another inside the curve. The outside wheels go a longer distance than the inside ones but in the same duration. The inside wheels have a lower speed as they travel a shorter distance using the same time as the outside ones.
Plus, the front and rear wheels travel different distances. Due to these differences in speed, a car needs a differential. Where you fix them depends on the drive system, whether it’s a 4×4, 2WD, or AWD.
The differential in a front-wheel-drive system is next to the transmission, and this unit makes up the transaxle. The one in a rear-wheel drive sits between rear wheels with a driveshaft connecting it to the transmission. The set-up is different in an all-wheel or 4WD because such cars have a third differential, a center differential responsible for distributing torque to the front and rear.
Does a 4WD need all of these? Yes, it does. It needs both the front and the rear one because a 4X4 uses all four wheels. On top of that, a 4WD has a transfer case to enhance the division of engine power by a differential. It can be a full-time or part-time transfer case.
Types of Differentials
Open Differential
In addition to being the oldest option, many manufacturers use it because it’s reliable and has a simple design. You’re likely to get it in most car models.
In an open differential unit, the wheel with the least resistance gets power during traction loss. Therefore, the stable wheel gets less engine torque. That’s different from a limited-slip differential that distributes power equally when you’re diving on a straight road and pumps more torque to the one with the most traction when there’s traction loss.
The open end’s drawback is that power still goes to a wheel without traction. Therefore, when you’re stuck, you may stay there for a long time. It makes open differentials unsuitable for off-roads used on rocky terrain or in high-speed racing cars.
Limited-Slip
It has so many similarities to an open differential, but it’s also very different. For example, when a wheel lacks traction, engine power shifts to another wheel to decrease spinning. That being so, a front-wheel drive with a limited-slip differential doesn’t spin from side to side. You can get this differential in a Nissan 370Z.
It’s suitable for wet and slippery roads. But, some limited-slip differentials wear out faster than others. Two types of limited-slip differentials are,
Mechanical Clutch
It has an integrated clutch system that locks the two sides of the axel together. Thus, it’s the choice in trucks towing large load capacities or in high-speed racers.
Though all limited-slip differentials do the same work, the process is different. For example, if your car has a mechanical clutch, the pressure rings push the clutch plates beside the gears to produce resistance.
Viscous Coupling
It’s different from the ones we’ve talked about already because it uses fluid movement to increase power on wheels. Thus, it has discs inside a fluid, and as you drive, if a wheel slips, the oil’s motion exerts pressure on the discs to rotate and transfer power to the wheel.
Torque-Vectoring Differential
It’s the modern technology we all desire. Torque-vectoring does the work automatically using computer data collection. It gathers data from the throttle position, the steering, and the driving conditions to create a power distribution plan.
Therefore, the traction generated when turning suits the situation on the road if you’re driving on snowy or slippery terrain. It’s the option in a Lexus RC F.
Locking Differential
It aligns wheel speed such that they all rotate at the same speed. A locking differential is the best choice for off-road cars. When the wheels on the same axle lock, you’re in better control as you turn the car because the set of wheels turns at once irrespective of each wheel’s traction.
Locking differentials aren’t demanding when it comes to maintenance. They are more durable than some limited-slip differentials, but wheel treads wear out fast. Thus, your car may have steering issues later, which will make driving on snow difficult. Jeep Wranglers have this differential.
When choosing a differential, you have to think about your off-roading terrain, the time spent off-road, how you drive and how much you’re willing to spend. You’ll make such decisions when your differential malfunctions.
How to Tell There’s a Differential Problem
Oil Leakage
You may confuse differential fluid with engine oil unless you take a closer look at the source of the leak. If the leak is on the axle, it might be differential fluid. If it continues leaking, it may damage the axle, transmission, or even the wheels. Plus, your car will run out of differential fluid.
An oil change ensures the transaxle unit functions efficiently. In a 4WD, you should change it after driving up to 60,000 miles. When you do so religiously, the differential lasts longer.
Strange Sounds
Nothing tells you there’s a problem in your car, like strange sounds. It might be a rattle or a whirring sound. It might not even be your differential, but whenever there’s an unusual sound, you need to have it checked.
When your differential produces a whining sound, it needs lubrication. You may want to inspect it for fluid leakage. If the pinion bearings wear out, they may create a peculiar sound.
Awful Smell
Expired fluid may thicken or release odor. Driving a car in that state may damage the gear or components. Further, such differential fluid may burn and leave a reddish stain. When that happens, the system needs repair and refill to function.
Vibrations
It doesn’t mean that all vibrations come from a faulty differential. We’re saying that if you experience them, don’t overlook differential failure as one of the causes. The vibrations can come from the driveshaft when a differential’s universal joints wear out. You’ll feel these vibrations when you accelerate or when the differential fluid leaks.
If you take time before servicing your car, you’re likely to have issues with most components. Therefore, schedule regular oil replacement depending on the manufacturer’s instructions.
Sometimes, the problem is not due to poor maintenance but a factory problem. For instance,
Toyota recalled Tacomas from 2016 and 2017 because the rear differentials had faulty nuts tightening that could cause a leak. Mercedes Benz also recalled over 2,000 cars with defective rear axles that could affect the alignment of the differential and cause driveshaft malfunction.
FAQs
Can a car run without a differential?
No, because it will travel in a straight line without turning as the wheels’ will revolve at equal speed and cover the same distance. If such a car has rear-wheel drive, it will skid from the push injected by rear wheels onto the front ones.
Does the front differential turn when not in 4WD?
Yes, it turns even when you switch to two-wheel drive due to the front wheel rotation. However, it doesn’t have a load until you switch to 4×4.
Is it safe to drive a car with a bad front differential?
No, it’s not, as it can get out of hand and put you and other road users at risk. It may also increase friction between metal components and wear out these surfaces. Thus, you’ll have weak gear.
All of these problems will increase your repair cost. Even when there’s partial damage, it may affect other parts and worsen the driving experience. Also, it’ll be hard to negotiate curves with a faulty front differential.
As we conclude, differentials are necessary, more so in a 4WD. They distribute engine torque so that wheels don’t rotate at the same speed because you need such variation when maneuvering curves or when some wheels lose traction.
Final Thoughts
Without differentials, your car would turn like a go-kart. But, differentials aren’t the same. Some cars have open differentials, while others use a locking differential.
The type of car dictates the differential in it. For example, high-speed racers may have a limited-slip mechanical clutch, while off-road trucks have a locking differential. The number of differentials is also different, with AWD and 4WD leading with three when rear-drive and front-drive have one each. Overall, a 4WD must have a differential.
