The differential is built into the gearbox case and utilizes the same lubrication in front-wheel-drive vehicles. The differential, which is situated at the back of a rear-wheel-drive (RWD) car, is commonly overlooked during normal maintenance.
The oil film that covers the rear differential fluid makes it possible for the differential’s gears to move around with ease.
Periodically, this fluid needs to be changed. Rear-wheel drive and some front-wheel drive cars and trucks use gear oil or differential fluid to lubricate the gears and bearings in their differential. This oily fluid has a high viscosity and can maintain lubrication even under extreme stress.
Differential fluid and gear oil are available in synthetic and conventional grades. Without this high-pressure gear oil’s lubricating properties, friction would quickly erode the special layer of hardened steel covering the gear teeth. The gears fail early as a result of this.
The purpose of this essay is to show you how easy and pleasant maintaining your rear differential is. We’ll also go into great detail about when to replenish the rear differential fluid as well as how to do so.
A Differential: What Is Its Definition?
Starting with the basics of the car differential, whether it be a gas, diesel, hybrid, or electric vehicle, let’s talk about them.
A certain amount of power is transferred from the engine to the wheels through a driveshaft, or by a front differential transaxle in the case of a front-wheel-drive vehicle.
To drive the pair of two wheels, the output of this driveshaft must be divided. Here is where differentials come into play.
They allow the wheels to move at different rates while distributing the power. What exactly is a differential, then? A vital component of the front or rear axle assembly is the differential.
You can turn thanks to it without having to wind up the drivetrain. Once the engine transmits its power through the gearbox to a driveshaft attached to it, the rear differential divides the available torque using a set of gears. These gears can change the number of rotations per minute that each wheel makes.
Why so? Well, consider what the front and back wheels would be doing simultaneously when a car made a straightforward left U-turn. Hence, the inner or left wheels must travel a great deal less distance than the outer or right wheels. The gearing of a differential enables this.
A typical rear differential by Dana60Cummins. Each rear wheel’s axle is connected to the driveshaft that leaves the engine at the rear differential. Three sets of gears are spinning, and each gear requires oil. However, it needs to be changed regularly, perhaps every 30,000 to 60,000 miles, but this can vary from vehicle to vehicle.
It will enable the outer tire to spin at a higher speed while the inner tire rotates at a lesser speed. A differential is what propels the wheels whether you’re operating a rear-, front-, or all-wheel-drive vehicle.
The differential’s gears transmit engine power to the axles when you depress the gas pedal. As a result, the wheels can spin on the axles in the right direction and at the right speed.
Then, What Exactly Is a Rear Differential?
Every vehicle has differentials, in some form or another. The differential, sometimes known as a transaxle, is situated in the front of front-wheel-drive automobiles.
The differential is in the back of vehicles with rear-wheel drive. Differentials are found in both the front and the back of four-wheel drive vehicles.
The driveline component known as the differential is located between the wheels, where the driveshaft joins the axle. Different wheel speeds are simply made possible by a differential.
For instance, when turning a bend, the outside tire must move faster to keep up with the inside tire. This is because the outside wheel travels farther than the inside wheel. Without a differential, your tires would skitter and bounce throughout a turn.
Which are the Different Categories of Differentials?
Open, limited-slip, and locked differentials are the three different categories of differentials that have existed for a long time. The list currently includes a few more instances as a result of advancements in drivetrain engineering.
Some electric vehicles come equipped with an integrated electric motor, which does away with the requirement for a typical car differential. The following is a list of the most common production-related differences:
1. The Open Differential
An open diff has two half shafts with gears at either end. The primary ring gear, which is connected to the driving shaft via a pinion gear, drives these gears.
A smaller spider gear that is static when the vehicle is moving straight ahead but engages when the vehicle is turning is located between the two half-shaft gears.
This difference has the benefit of being easy to make and operating perfectly in most circumstances. Power usually follows the path of least resistance, which is a disadvantage. In low-grip situations, the wheel will eventually start to spin aimlessly.
When accelerating hard, some FWD performance vehicles with an open differential may experience torque steer. People often ponder whether they can slide with an FWD automobile because of this.
2. The Locking Differential
In essence, a locking differential is an open differential with the additional capability of locking the wheels in place. This results in an axle that is effectively fixed because both wheels are moving at the same speed.
The typical target market for this kind of differential is off-roaders. As you may imagine, it is pointless to attempt to climb a rocky incline with one wheel spinning freely. When both wheels are rotating at the same speed, a truck or an SUV will have more traction.
Hardcore off-roaders also have front differential lockers for optimum off-road traction. For instance, lockers for the front and back of a Jeep Wrangler Rubicon are readily available.
3. The Limited Slip Differential
A limited-slip differential (LSD), though normally only seen in performance rear-wheel drive (RWD) cars, combines the best of both worlds. With the help of an LSD, the two wheels can spin independently, but only up to a specific speed.
The rear differential assembly by Dana60Cummins. When the differential needs to be emptied for axle maintenance, replacing the rear differential fluid is a fantastic idea. To find out the right intervals, it’s always a good idea to review your owner’s or auto maintenance manuals. Ordinary oil cannot survive the tremendous forces delivered by the differential gears’ continuous lashing.
Since it improves traction, the vast majority of high-performance sports car models as well as serious four-wheel-drive (4WD) cars have this function. Mechanical clutch versions and viscous LSDs are the two different types of LSDs.
Pressure rings on the clutch plates close to the gears are a feature of the mechanical clutch LSD. The differential locks as a result. For instance, here is how Toyota Tacoma’s Auto LSD system operates.
The clutches can also be electrically controlled, which is how most all-wheel-drive cars function. However, all-wheel-drive (AWD) vehicles, which are frequently front-wheel-drive most of the time, can include a center differential that is electronically engaged to engage the rear wheels.
A viscous LSD may be set up much more easily. The aforementioned clutch plates are replaced by a thick, viscous fluid. This liquid stiffens and locks the differential when pressure is applied to it.
If it gradually loses its viscosity, issues might occur. Yet routine upkeep should keep it in good condition (as is knowing how to reset the maintenance light on Toyota Corolla).
4. The Torsen Differential
The setup of a Torsen differential is the same as an open differential, except there are extra “worm gears” around the bevel gears. A Torsen differential is typically in the open position, dividing torque evenly between the front and rear axles.
When a wheel on a specific axle starts rotating more quickly than the opposing wheel, it performs differently. In that case, the worm gears and pinion gears engage one another and impart torque to the slower-rotating wheel.
The Torsen differential supports a variety of worm gear configurations, enabling manufacturer customization.
5. The Active Differential
Unlike a limited-slip differential, which controls its clutches mechanically, this differential regulates its clutches electronically. While pricey, this approach has several benefits.
The vehicle’s ECU can make millions of calculations per second to identify which wheel needs to be powered when it is equipped with several sensors.
6. The Torque Vectoring Differential
This is a step up from the typical limited-slip diff. A torque vectoring system can limit power on one side and increase torque when there is a considerable speed differential.
Instead, clutches are used to lock the differential. This is typically used by high-end performance vehicles because it allows for a sharper turn-in. Torque vectoring and rear-wheel steering enable a larger vehicle to operate more nimbly.
The Rear Differential Fluid: What Is It?
The driveshaft that leaves the engine at the rear differential is attached to an axle for each rear wheel. There are three spinning sets of gears, and each gear needs oil.
Regrettably, it must be replaced at regular periods, such as every 30,000 to 60,000 miles, although this can vary from vehicle to vehicle. Rear differential fluid replacement is a wonderful idea when the differential needs to be emptied for axle servicing.
But it’s always a good idea to consult your owner’s or auto maintenance manuals to determine the proper intervals. Regular oil is unable to withstand the immense forces the differential gears’ continual lashing delivers.
The oil must be able to absorb the shocks and loads created when engine torque and horsepower are delivered to the wheels.
Up until the 1970s, when commercial whaling was outlawed, sperm whales were used to make a sizable amount of this high-pressure lubricant. Modern synthetic substitutes have now supplanted these chemicals.
What are the Symptoms of Low Levels of Rear Differential Fluid In a Car?
Here are the warning signals to watch out for, whether you have low differential fluid or an outdated fluid that has to be changed:
The ARB air-locking rear differential by Richard Harvey / CC BY-SA 3.0. You likely have a rear differential leak that has to be corrected if the fluid level is low or it is blending with water. The rear cover of the housing’s housing is frequently the source of a differential leak, and replacing the cover or the gasket should fix the problem.
1. Grinding or Whining Sounds
Whining and/or grinding noises are the most typical indications that you have differential problems. Insufficient or outdated fluid will result in improper lubrication of the gears. As a result, there is extra friction between the gears, which frequently produces whining, grinding, or both noises.
Of course, differentials aren’t the only component in a car that may make odd noises. For example, faulty wheel bearings might cause a whining noise akin to differential noise. To distinguish between them, you’ll need to pay attention to how the noise changes.
Depending on the vehicle’s speed, wheel bearing noise varies. In the meantime, engine load and vehicle speed affect differential noise. Going up a hill can help you distinguish between them because you have to use more power and your engine is working harder, but you won’t be moving very quickly.
A differential issue is most certainly present if the noise worsens as you attempt to climb. But, if the noise only gets louder as the vehicle speeds up, a wheel-bearing issue is more likely to be the cause.
Note that similar noises can also be made by worn tires, however, they usually vary depending on the condition of the road. Differential and bearing noise, however, do not.
2. Presence of Burning Odor In the Car
Low or poor differential fluid, as noted, will cause the differential to become more frictional. More friction generates additional heat, and when it gets hot enough, it may emit a burning odor.
It should be simple to spot if your vehicle has rear-wheel drive because the stench will be coming from the back of the vehicle.
With vehicles that have the differential at the front and the transmission there, it becomes a little bit trickier. Hence, the differential, transmission, or even engine may be to blame for the odor.
Any burning odor should be taken seriously. It’s a smart idea to pull over and investigate the source of the stench if it doesn’t go away in a minute or two. To reduce the damage in the event of a fire, it is also always a good idea to keep a fire extinguisher in your car.
3. Unusual Vibrations
Problems with the differential may result in vibrations throughout the entire vehicle because it transfers power.
Of course, the car’s vibrations can also be caused by other parts. You most likely just require a tire balance if the vibration on the steering wheel only happens at speeds more than 40 mph.
That can indicate a problem with your differential or low fluid if it happens even at low speeds and changes with engine load. Also, when cornering, it is more likely to emerge.
Be aware that a poor transmission can also create vibrations, but that this condition is more likely to be accompanied by surging and/or trouble shifting.
How Do You Examine Your Rear Differential Fluid Levels?
Keep in mind that the aforementioned symptoms can also appear if the differential has failed. Often, this occurs when the gears are worn out. To determine whether there is a fluid problem or a defective differential, you must check your differential fluid.
It’s simple to check the rear differential fluid in a car with rear-wheel drive:
- Find the filler plug for the differential. Check your repair handbook to make sure; this should be on the front side of most differentials.
- Remove the plug, then place your finger inside the port.
- If you have large fingers, use your pinky to prevent being stuck. Your finger should have oil or fluid on it.
- Your problems are caused by low differential fluid if there is no fluid on your finger.
- Inspect the fluid as well. It should resemble motor oil and be a clear brown color. Change it now if it’s black and/or gunky. You will also need to change it if it turns a light brown color, similar to chocolate milk, which indicates that the fluid is mixing with water.
A RAM 3500 rear differential by Dana60Cummins / CC BY-SA 3.0. Rear differential repairs can end up being expensive if the wrong gear oil is used and recommendations made by professionals are questioned. It is crucial to take the needs of the limited-slip or traction-sensing differential into account when choosing a differential fluid.
It should be noted that neither cars nor water should be mixed in the differential fluid. So, if the fluid level is low or it is blending with water, you probably have a rear differential leak somewhere, which needs to be fixed.
A differential leak frequently originates from the space between the housing’s rear cover and its housing, and either changing the cover or the gasket should resolve the issue. If everything appears to be in order, look for damage to the housing because road debris can cause cracks.
It is best to have your differential examined by a specialist if you think you may have a poor differential. Our article on differential repairs has more information.
How Can You Choose the Correct Rear Differential Fluid for Your Car?
The right viscosity or weight should be considered while picking a differential fluid. The GL rating is the following. Use only what is advised for your differential, if possible. There is just one course of action if the manual calls for a 90W gear oil with a GL-5 rating: use it.
Using the wrong gear oil and questioning the experts’ decisions can ultimately lead to costly rear differential repairs. While selecting a differential fluid, it is important to consider the needs of the limited-slip or traction-sensing differential.
In a typical or “open” differential, the torque or twist generated by the driveline is always applied to both wheels. This occurs whether or not one of those wheels is helplessly spinning on an icy surface.
When this energy is wasted in the case of a limited-slip differential (LSD), it is detected and torque is switched to the wheel with the most traction.
Numerous mechanisms contribute to the wonder of redirected traction. However, the bulk of them requires friction modifiers unique to their particular design to work effectively.
Without these specific lubricants, an LSD will work poorly at best and fail at worst. The rear differential will need to be rebuilt and repaired, which will cost a lot of money. Use gear oil that is prepared with the proper friction modifiers for that LSD if your car has one.
The Rear Differential Fluid Change: Why Is It So Essential?
Depending on how the differential is constructed, this job could be either highly messy or quite neat. While some differentials have a drain plug, others need you to remove the housing cover.
In any circumstance, a sizable catch pan is required. It could be a good idea to place a plastic drop cloth underneath it as well.
You’re going to probably get dirty during the procedure, so change into your dirty clothing. Drive your automobile for a while to warm the oil before you start the procedure.
It only involves replacing the oil, right? Nothing is difficult, but prepare yourself. The worst smell that exists is from spent differential oil in vehicles.
There are two primary car differential designs and both call for the replacement of the differential fluid. The first one is easier to change and has a top-fill plug and a bottom-drain plug. You must remove the lid for the second type.
You probably don’t need to raise the vehicle if you’re changing the differential fluid in a tall SUV or truck. If you can’t, make sure to raise your car’s front and back to the same level. If not, you won’t be able to completely drain the fluid and add the right amount of fresh fluid.
The Rear Differential Fluid Change for a Differential with a Drain Plug
The initial step in this process is to clean the area around the fill (top) and drain (bottom) plugs. You don’t want the new fluid and any dirt to mix inside the housing. The next step involves opening the fill plug.
The Torsen differential by NocturnalA6 2.7 / CC BY-SA 4.0. An LSD will function badly or not at all without these particular lubricants. The rear differential will require rebuilding and repairs, which will be very expensive. If your vehicle has an LSD, use gear oil that has been specially formulated with the appropriate friction modifiers.
If your fill plug gets stuck, it’s preferable to figure it out now while your car is still safe to drive than to wait until the differential is empty. Remove the drain plug after you remove the fill plug. After that, use a pan to catch the used liquid.
Because the smell of used gear oil is so bad, you might want to do this outside. After emptying the differential, correctly reinstall the drain cap. If there is a washer, make sure to replace it because doing so will help to prevent leaks.
Fresh fluid should then be poured into the differential. While some vehicles require a differential fluid pump, others have enough space for you to pour from the bottle. To find out where the fill line is on your car, consult the owner’s manual.
Full, however, frequently denotes that the liquid is dripping out the orifice. But, take care not to overfill. If not, your differential risk turns into a fluid mixer. Replace the washer if necessary and then insert the fill plug.
The Rear Differential Fluid Change for a Closed-Case Differential
For this kind of differential, the entire rear housing must be removed. It is untidy and involves more labor because you have to re-seal the lid. As before, remove the fill plug before releasing each differential bolt. Lower bolts should be removed, and some slack should be left in the top bolts.
The differential may begin to leak as soon as the bottom nuts are released. It could, however, also get stuck. Use a flat screwdriver from your Blue Point toolkit to attempt to loosen the case, being careful not to bend the flange. Let the water drain, then take off the cap.
Wipe the inside of the housing and the lid to remove any remaining gear oil and the metal shavings in them. Then, using a razor scraper or a mildly abrasive pad, clean the mating surface of the housing and the cover. Use brake cleaner or anything similar to clean and wipe.
While some automobiles utilize a gasket, others use gasket material, which is a particular form of silicone adhesive designed to seal in the oil. Apply a single bead (thicker isn’t always preferable) around the cover and in each hole, then bolt the cover into place.
After giving the gasket maker the recommended amount of time to dry, tighten the cover to your vehicle’s requirements. Don’t make it too tight, please.
How Much Does the Rear Differential Fluid Change Cost?
The cost of replacing your differential fluid will be a little more expensive than the cost of adding engine oil. The cost to replace the fluid in the front differential is different than the cost to replace the fluid in the rear differential.
It will cost somewhat more overall to replace the rear differential fluid. It averages from $80-$150. The labor to change the rear differential fluid costs between $50 and $70, and the fluid itself is priced between $30 and $80.
By being informed of the typical rear differential servicing cost for your car, you may keep costs down and prevent any unnecessary repairs or replacements. The expense of differential fluid replacement can be kept as low as feasible by being aware of the symptoms and warning indications.
A Nissan rear differential by RB30DE~commonswiki / CC BY-SA 3.0. A bit more money will be spent on replacing your differential fluid than on adding engine oil. Changing the fluid in the front differential will cost more money than doing the same for the rear differential.
What Factors Influence the Rear Differential Fluid Change Costs?
1. The Labor Rates In Your Area and Location
Depending on where you live, there are different labor rates for mechanics. Certain areas of the country have lower labor expenses than others.
In addition, the labor rate in the country is often much lower than in the city. Going to the local lubricant business will be less expensive than taking your car to the dealership.
But, you get what you pay for and the car will be maintained by less experienced technicians if you don’t go to a shop with skilled professionals.
The most affordable solution would be for you to complete the task on your own. If you have the right equipment and skills, changing the differential fluid yourself could save you money.
2. The Required Quantity of Differential Fluid
Differential oil is priced differently, just like engine oil. If you decide to use synthetic oil, your expenditures will increase. You pay extra for various qualities as well as consistency. Remember that the type of oil needed for each differential can vary.
It’s also important to consider the required amount of differential oil. Each axle has a different amount of gear grease stored there. Most systems will only require one gallon or less during a change. Further details about this are available in your service manual.
The DIY Rear Differential Fluid Change Process
Undoubtedly, you’re considering whether you can complete the task yourself to save money. Although it is doable, the procedure can be a little challenging because it entails taking off the differential housing cover. It is more complicated than, say, changing the engine oil.
We would rather save ourselves the effort and let the experts handle the situation. Nonetheless, if changing your differential fluid is something you’d like to learn how to do, here’s what you should get ready for:
- Standard hand tools, such as a torque wrench
- A catch pan for oil
- A fresh differential gasket, or RTV sealant if the vehicle doesn’t have one
- Cleaner for brakes
- A paper towel or rag for cleaning
- A screwdriver with a flathead
- A plastic scraper
- A pump for transferring fluid
- If you have a limited-slip differential, use limited-slip differential additives. You don’t need this, though, if the gear oil you’re using already has the additives
- The differential’s gear oil. The most popular oil is the 75WG90 GL-5, but to be sure, check your service handbook
The pinion shaft of a rear differential by Aconcagua / CC BY-SA 3.0. The overall cost of replacing the rear differential fluid will be slightly higher. The range is often $80-$150. The fluid for the rear differential is priced between $30 and $80, and the labor to change it is between $50 and $70.
If your car has a limited-slip differential, especially the viscous-type (VLSD), which operates with silicone-based fluid, you should double-check. Damage and additional issues will result from using the incorrect oil or fluid. It’s best to use the oil that your car manufacturer recommends.
This is a general instruction on how to replace the fluid in your rear differential, albeit the procedure may vary based on the make and model of your car:
The Rear Differential Fluid Change: A DIY Step-By-Step Guide
- If you require additional space, jack up the automobile and place it on jack stands.
- Starting at the rear of the differential, remove all the bolts holding the housing cover in place. But, DON’T take out the top bolt.
- Using a flathead screwdriver, pry the lower portion of the differential. Make sure the oil collection pan is underneath because the liquid will start to pour out right away.
- Remove the top bolt and the housing cover as soon as the fluid stops dripping.
- Brake fluid should be used to clean and wipe the housing cover. Clean the differential and the cover’s contact surfaces. For tough residue, use a plastic scraper.
- Use RTV sealant or a gasket on the differential housing cover.
- Hand-tighten the top and bottom bolts after reattaching the cover to the housing. Next, tighten the remaining bolts in a star pattern, but be careful not to overdo it. If RTV sealant was used, tighten it until the sealant escapes through the holes. Give it at least an hour to sit.
- Use a torque wrench to tighten the bolts, and consult your service manual for the recommended torque levels. Once more, start at the top and bottom and work your way down in a star-shaped manner.
- Use a fluid pump to refill the liquid. Don’t forget to mix it with LSD additions if necessary, and fill it to the brim. Follow the directions on the additive and in your service manual because the requirements are frequently different.
- Install the plug again.
Again, the procedure may vary slightly based on the brand and model of your car. And our tutorial just offers general guidance on how to carry it out.
A lengthy time of optimal differential performance is guaranteed by differential fluid. The gear oil, also referred to as differential fluid, is kept inside the axle housing.
Gear oil is designed to function under high pressure, as opposed to engine oil, which is designed to function at high temperatures.
Metal-on-metal contact would cause the differential to overheat if there wasn’t any differential fluid.
That suggests that it would ultimately burn out, maybe represent a safety danger, and require expensive repairs. The expense of replacing the front or rear differential has been previously examined.
Generally speaking, the differential fluid should be replaced every 30,000 to 60,000 miles; however, for exact maintenance advice, always consult your owner’s handbook.
This repair technique is on the intermediate level. Changing the fluid is easier than, say, correcting a front differential leak.
In vehicles with reduced ground clearance or suspension components that block the differential cover, it could become difficult.
Have a professional analyze the differential if you are unclear about what to do. But, keep in mind that you shouldn’t cut corners when replenishing the differential fluid.
Jim Wicks is the founder of MotorVehicleHQ. With over two decades of experience in the automotive industry and a degree in Automotive Technology, Jim is a certified car expert who has worked in various roles ranging from a mechanic, car dealership manager, to a racing car driver. He has owned more than 20 cars over the past 15 years. Ask him about any vehicle you see on the road and he can tell you the make, model and year. He loves the aesthetics of all things cars, and keeps his vehicles in pristine condition.
In his free time, Jim enjoys getting his hands dirty under the hood of a classic car or taking long drives along the country roads. His favorite car? A 1967 Shelby GT500, a true classic that, according to Jim, “represents the pure essence of American muscle.”