A differential is the part of a vehicle's drivetrain that allows two wheels to turn at different speeds. Differentials have one input and two outputs, with each output going to an axle or driveshaft that then connects to a wheel.
 |
| rear differential |
What is a differential used for?
When you turn in your vehicle, the left and right wheels take a slightly different path. The tires on the inside of the turn will form a circle with a smaller radius, which means it takes fewer revolutions of the tire to complete the turn.
If the vehicles were not equipped with front and rear differentials, the left and right tires would be forced to spin at the same speed despite these different paths. This would cause one or both tires to spin, resulting in loss of traction, excessive tire wear, and additional stress on other powertrain components.
The difference in speed between the two tires is due in part to the vehicle's track width (i.e., the distance between the left and right wheels). The wider the track and the tighter the turn, the greater the speed difference between the inside and outside wheels.
How many differentials does my vehicle have?
Vehicles have a different number and placement of differentials depending on the number of drive wheels they have. Drive" wheels are the wheels that receive torque from the engine.
Front and rear wheel drive vehicles are two-wheel drive vehicles. They have only one differential.
Front Wheel Drive
Front-wheel drive vehicles often have a transaxle, which is a single integrated unit that serves the transmission, differential and axle. On front wheel drive vehicles, the term "transaxle" can be used interchangeably with "transmission" or "differential" depending on who you talk to.
Rear Wheel Drive
Most rear-wheel drive vehicles will have a stand-alone differential between the rear wheels that is linked to the transmission via a driveshaft. A rear differential is colloquially referred to as a "rear" or rear differential by some people.
All-wheel drive
All-wheel drive vehicles have three differentials: a front, rear and center differential. The center differential splits torque between the front and rear differential inputs, which each split the remaining torque from left to right.
Four wheel drive
Four-wheel drive systems found on trucks and SUVs usually have a transfer case instead of a center differential.
Types of Differentials
Open Differential
An open differential is the simplest and most common differential. Equal torque is applied to both outputs. This means that if one tire loses traction, the other tire will be limited in the amount of force it can apply to the ground to propel the vehicle forward.
Locking Differentials
Locking differentials are typically found on specially designed off-road vehicles, such as trucks and jeeps that come with off-road packages.
A locking differential turns the left and right wheels at exactly the same speed, regardless of wheel slip. This differential is ideal for rough terrain where a tire may be in mud, snow or even air.
You must be careful not to lock the differential in a high-grip situation, such as on dry asphalt. Doing so could put undue stress on the drivetrain and damage expensive components.
Limited Slip Differential
A limited-slip differential is a middle ground between an open differential and a locking differential. They are typically found on sports cars and high-end luxury cars.
There are many different types and implementations of limited slip differentials. The basic idea is that when a tire slips, the maximum wheel speed of a slipping tire is limited. The torque is then transferred or multiplied to the opposite tire that still has traction. Ideally, this allows a vehicle to continue moving forward even if one tire has little or no traction.
Bad front or rear differential symptoms
There are a few visible signs that will present themselves if your front and/or rear differentials begin to wear or become damaged. Here are the most common symptoms you can expect if your differential is going bad.
Read also: What Is a Front Differential and Why Should You Know?
1) Whining noises
Whining noises are one of the most common and visible symptoms of a bad differential. This could be because the components of the differentials are not properly lubricated.
Perhaps the differentials are leaking fluid and this is causing them to wear out prematurely. Whenever their components are not lubricated properly, you will probably hear whining noises coming from the end of your car where the differential is located.
2) Tire Damage
If your left and right tires are running at the same speed when you turn a corner, the inside tires will wear more because they are forced to turn faster than they should. This will cause your tires to wear out prematurely.
If your differential is locked, you may also experience tire rubbing, which is the sound of your tires grabbing and sliding in quick succession. Depending on the rubber compound, this may sound like a rapid scream or a chirp. There will likely be vibrations in the rhythm of the sound.
3) Difficult to handle
Differentials allow your vehicle to turn comfortably when you make a turn. A failing differential is likely to disrupt your vehicle's turning ability and make it unstable.
Whenever you notice handling difficulties while turning or cornering, take your vehicle to a mechanic as soon as possible to have it checked.
4) Vibrations
If the universal joints in your differentials become too worn, the driveshaft will start to vibrate. You'll feel the vibrations even more when you step on the gas pedal to accelerate your vehicle. The vibrations are even worse if there is a differential fluid leak.
While this may not seem like a big deal, it should be a warning sign that you need to have your differentials checked.
5) Grinding the gears
If you have a worn differential, its gears may start to grind more. This can even cause humming noises from the grinding of the gears. You will hear the humming getting louder as you accelerate the vehicle.
If you hear this, it's a good idea to have your differential inspected, and maybe the transmission as well. If you catch it early, the solution could be as simple as a gear oil change.
Cost of repairing the front or rear differential
The average cost of repairing faulty front and rear differentials will depend on the severity of their condition. Generally speaking, it shouldn't cost more than $400 to repair most front or rear differentials. Most people pay around $200 to $300.
This would involve repair work related to adjusting the play and replacing the oil seal on a differential. But if you have to completely rebuild a differential, your repair costs will be between $400 and $800.
That's still cheaper than having to replace an entire differential, which would cost between $1,000 and $2,000.
SYMPTOMS OF BAD DIFFERENTIAL