The differential is a set of gears that allow the drive wheels to rotate at different speeds. As with any other set of gears in your car, it needs lubrication to minimize friction. This ensures they don’t wear out quickly and keep the temperature in check. So, is a differential fluid change necessary?
The short answer is yes. Differential fluid or oil will eventually lose its lubricity. Whether it’s due to age or due to a leak, oil and other lubricants need changing at some point. Here’s everything you need to know about differential fluid change:
How Does A Differential Work
Before we discuss differential fluid change itself, let’s understand the basics of differentials first and why they’re important. This will give you an idea of why it needs maintenance, and why you should care for it. The differential is a set of gears inside a round housing usually made from carbon steel.
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Every car has a differential for its drive wheels, including front-wheel drive cars. As mentioned, their purpose is to allow the driven wheels to rotate at different speeds during cornering. This is necessary since the outside wheel will have to rotate faster than the inside wheel since it has to travel a further distance.
For example, if you’re turning right, then the left wheels are the outside wheels and the right wheels are the inside wheels. The outside wheel will have to cover a longer distance. If they can’t rotate faster, the outside wheel will have to slip to keep up with the inside wheel which is not pleasant and can wear out the tires and other components quickly.
There are several types of differential, but most “normal” cars usually have an open differential. This sort of differential works by using spider gear. When it detects the car is going through a corner, the spider gear will allow the outside wheels to spin faster. The video above should give you a better idea of how the system works.
Regardless of the type you have, they all work by using a set of gears and they all need lubrication. Most carmakers specify that you should change your differential fluid every 50,000 miles or so. Speaking of differential types:
Other Types Of Differential
Let’s briefly discuss the different types of differential:
- Locking differentials are largely similar to an open differential, but it has the ability to lock the wheels together and force them to spin at the same rate regardless of the condition. This is great for offroading and getting a stuck car out.
- Limited-slip differentials (LSD) have several variations. But the main idea behind all of them is to lock the wheels to limit slip and allow for better traction. They’re similar to locking differentials, but they’re more dynamic. Whereas locking differential usually requires driver input to lock.
- Torque vectoring is similar to electronic LSDs, but takes it further by utilizing more sensors and computing power. This type of differential can divert up to 100% of the engine’s power to an individual wheel, allowing for better traction in almost any condition.
- Welded differentials are the exact opposite of all other differentials. As the name suggests, this differential is welded so that the wheels rotate at the same rate no matter what. This induces spin on the inside wheel and helps the car to initiate and maintain a drift. Great for drifting on a budget.
Again, regardless of the type of differential you have in your car, they all need lubricant to work properly and prevent premature damage. Needless to say, complex systems such as LSDs and torque vectoring will be very expensive to repair, so you’ll want to take extra care.
Differentials are complex and fascinating, and we can spend an unhealthy amount of time talking about them. And we already did, you can learn more about how they work in our guide to types of differential.
Front Differential Fluid Change
As mentioned, all cars have a differential of some sort. Whether you have front, rear, or all-wheel drive, the driven wheels must have a differential to allow the driven wheels to rotate at different speeds during cornering. The non-driven wheels don’t need it as they don’t connect to the wheel on the opposing side, so they can spin freely.
However, note that many front-wheel drive cars often integrate the differential in the transmission housing. And they share the same fluid (i.e. the transmission fluid). So, you probably don’t need a differential fluid change. Instead, changing the transmission fluid is enough.
While this is the case for most front-drive cars, it’s good to double-check. You should check your car’s service manual or with a trusted mechanic on whether or not your front-drive car uses a separate fluid for its differential.
Signs Of Low Differential Fluid
Whether you have a low differential fluid or an old fluid that needs changing, here are the signs to look out for:
1. Whining Or Grinding Noises
The most common sign when you have differential issues is whining noise and/or grinding noises. If the fluid is old or low, then the gears aren’t properly lubricated. This creates excess friction between the gears, which can often result in a whining or grinding noise or both.
Of course, differentials aren’t the only thing that can create weird noises in your car. For example, bad wheel bearings can create a whining noise similar to differential noise. You’ll need to pay attention to how the noise changes to tell them apart.
Wheel bearing noise changes depending on vehicle speed. Meanwhile, differential noise changes depending on the vehicle speed and engine load. An easy way to tell them apart is by going up a hill; when driving up a hill, you’ll have to increase power and engine load, but your car won’t be going fast.
If the noise gets worse as you try to climb, then it’s likely a differential problem. But if the noise only gets worse with speed, then it’s more likely to be a wheel-bearing problem. Note that bad tires can also produce similar noises, but they typically change depending on the road surface. Whereas differential and bearing noise does not.
2. Burning Smell
As mentioned, low or bad differential fluid will increase friction in the differential. More friction results in more heat, and if it gets hot enough, it can produce a burning smell. If you have a rear-wheel drive car, it should be quite easy to identify as the smell will be coming from the back of the car.
However, it’s a bit more tricky with cars that have the differential at the front since the transmission is also at the front. So, the smell could come from the differential or the transmission, or maybe even the engine.
In any case, a burning smell is a cause for concern. If the smell doesn’t go away in a minute or two, it’s a good idea to stop driving and check where the smell is coming from. Also, always a good idea to have a fire extinguisher in your car to limit the damage in case of a fire.
Since the differential is responsible for transferring power, issues with it can cause vibrations throughout the car. Of course, other components can cause vibrations in the car. If the vibration only occurs on the steering wheel at speeds above 40mph, then you probably just need a tire balancing.
However, if it occurs even at low speeds and changes with engine load, this could mean your differential is bad or the fluid is low and it’s causing issues. It’s also more likely to appear when cornering. Note that a bad transmission can also cause vibrations, but it’s likely accompanied by surging and/or difficulty changing gears.
Checking Your Differential Fluid
Note the symptoms above can also come up when the differential has gone bad. This usually happens when the gears have worn out. So, you’ll need to check your differential fluid to differentiate whether it’s a fluid issue or you have a bad differential.
If you have a rear-wheel drive car, checking the rear differential fluid is quite easy:
- Locate the differential’s filler plug. Most differentials should have this on the front side of the differential, check your service manual to be sure.
- Take out the plug, and insert your finger into the port.
- Use your pinky if you have large fingers so it won’t get stuck. There should be oil/fluid on your finger.
- If there’s no fluid on your finger, then your differential fluid is low and that’s the source of your troubles.
- Additionally, inspect the fluid. It should be a clear brown color similar to engine oil. If it’s black and/or gunky, it’s time to change it. If it’s light brown like chocolate milk, this means the fluid is mixing with water and you’ll need to replace it as well.
Note that cars don’t consume differential fluid, nor should it be mixing with water. So, if the fluid is low or it’s mixing with water, you likely have a leak somewhere and you’ll need to repair that.
A differential leak often comes from the gap between the housing and its rear cover, and replacing either the cover or the gasket should fix it. If it seems fine, check the housing for signs of damage as road debris can cause cracks.
Rear Differential Fluid Change Cost
As mentioned, front-wheel drive cars usually have their differential integrated into the transmission housing. And they typically use transmission fluid as a lubricant, so you don’t need to change the fluid separately.
If this is the case for you, changing your transmission fluid will cost between $100 to $250 on average. Most cars will require you to change the transmission fluid every 60,000 miles or so, but check your service manual to be sure.
So, we’ll focus on rear differential fluid change in this section. We’ve learned how important it is and how to check it, but how much will it cost to change your rear differential fluid? On average, it costs between $80 to $150 in most cars.
The cost includes labor which is usually around $60 to $80, and the rest is for the differential fluid itself. This cost also applies to the front differential if your car just so happens to use separate fluids from the transmission.
Note that the cost might be higher if you have a car with a limited-slip differential or torque vectoring. These differentials usually need additives and in some cases specialized gear oil for their operation. And for luxury cars, it’s likely to be higher if you do it at the dealer since they often charge a premium.
Rear Differential Fluid Change
Of course, you’re probably wondering if you can do it yourself to save some money. While it’s possible, the process can be a bit tricky as it involves removing the differential housing cover. It’s not as straightforward as, for example, changing the engine oil.
We prefer to leave the job to professionals and save ourselves the trouble. But if you’re interested in learning how to change your differential fluid, here’s what you need to prepare:
- Common hand tools, including a torque wrench.
- An oil catch pan.
- A new gasket for the differential or RTV sealant if your car doesn’t use one.
- Brake cleaner.
- Cleaning rag or paper towels.
- Flathead screwdriver.
- Plastic scraper.
- Fluid transfer pump.
- Limited-slip differential additives if you have a limited-slip differential. However, if the gear oil you’re using already has the additives then you don’t need this.
- Gear oil for the differential. The most common oil is the 75WG90 GL-5 but you should double-check with your service manual to be sure.
You’ll want to double-check if you have a limited-slip differential in your car, especially the viscous-type (VLSD) since it uses silicone-based fluid for its operation. Using the wrong oil or fluid will cause damage and further problems. Best to use the oil specified by your carmaker.
Additionally, the process might be different depending on your car’s make and model, but here’s a general guideline on how to change the fluid in your rear differential:
How To Change Differential Fluid
- Jack up the car and put it on jack stands if you need more space.
- Start by removing all the bolts holding the housing cover, which is at the rear part of the differential. But DO NOT remove the top bolt.
- Pry the lower part of the differential with a flathead screwdriver. Make sure you have the oil catch pan underneath as fluid will immediately start to pour out.
- Once no more fluid is pouring out, remove the top bolt and the housing cover.
- Clean the housing cover with brake fluid and wipe it clean. Clean the contact surface of the cover and the differential. Use a plastic scraper for stubborn residue.
- Apply gasket or RTV sealant to the differential housing cover.
- Attach the cover back onto the housing, then hand-tighten the top and bottom bolt. Then screw in the rest of the bolts in a star pattern, but don’t overtighten it. If you used RTV sealant, tighten it until the sealant comes out between the gap. Let it sit for at least an hour.
- Tighten the bolts with a torque wrench, check your service manual for the specifications. Again, start with the top and bottom, and then do it in a star pattern.
- Refill the fluid with a fluid pump. Fill it until it overflows, and don’t forget to mix it with LSD additives if necessary. The requirement is often different, so follow the instructions on the additive and your service manual.
- Reinstall the plug.
The video above from ChrisFix will give you a visual guide on how to do it. Again, the process might be slightly different depending on your car’s make and model. And our guide only serves as general instruction on how to do it.
Car Differential Fluid Facts: What You Need to Know
- Differential fluid, also known as differential oil or gear oil, is an essential car fluid that is often ignored.
- Signs of low differential fluid include unusual noises, vibrations, tire spinning, and burning smells.
- To check car differential fluid, you need to find the fill plug, release it, and let the fluid drain out into an oil drain pan.
- It is recommended to change the differential fluid every 30-60 thousand km driven by a professional because it needs to be cleaned properly before new fluid is poured in.
- Changing the differential fluid is important because it prevents damage caused by heat and friction to the components of the differential, which could lead to expensive repairs.
- You can change the differential fluid yourself if you have the necessary tools, or you can have a professional service provider take care of it for you.
- When adding new differential fluid, make sure you use the appropriate type of fluid for your vehicle and fill it properly.
- Unusual noises, vibrations, and tire spinning are enough reasons to take your car for a professional inspection.
- Low differential fluid can cause serious damage to your vehicle and even lead to fatal accidents.
- You can buy differential fluid and other auto parts online, but it is always recommended to consult professional help if you are not sure how to change the fluid yourself.
FAQs About Car Differential
We get a lot of questions about car differentials, and here are the answers you might find helpful:
What Is A Differential
A differential is a set of gears that allows the car’s drive wheel to rotate at different speeds. This is necessary since the outer wheel needs to rotate faster during cornering as it has to travel a further distance than the inner wheel. Without the differential, the inner wheel will slip to follow the rotational speed of the outer wheel. This is uncomfortable and will wear out tires and other components.
How Does A Differential Work
There are several types of differentials, but the gist of it is they work by using either a gear or a clutch pack that allows the wheel to rotate at different rates. The most simple type is the open differential, where a spider gear will allow the outer wheel to rotate faster when going through a corner.
How Often To Change Differential Fluid
Most carmakers recommend changing the differential fluid around 50,000 to 60,000 miles. Check with your service manual to be sure.
How To Change Differential Fluid
If you have a front-wheel drive car, the differential is often integrated with the transmission and uses transmission fluid as a lubricant. So, you don’t need to change it, just make sure to keep up with your transmission fluid change. If you have a rear-wheel drive car, then changing the fluid entails removing the differential housing cover and allowing for the fluid to pour out. Then you’ll need to install it back with a new gasket or sealant, and then refill the fluid through the filling plug.
How Much To Change Differential Fluid
A differential fluid change typically costs $150 at most, this is the case if you have an open or locking differential. It’s likely to cost more if you have a limited-slip differential (LSD) or a torque-vectoring differential as they’re more complex and sometimes require specialized gear oil for their operation.
Never Change Differential Fluid
This is a common misconception that for some reason is going around the internet. But you should change your differential fluid, there’s no reason not to. Every type of lubricating fluid in your car will eventually wear out, and sometimes they can become contaminated. So, it’s a good idea to change your differential fluid when the time comes. Perhaps the fear comes from the fact that changing the fluid requires you to remove the housing cover, which can compromise the integrity of the housing. But as long as you do it properly and install the gasket/seal correctly, there’s nothing to worry about.
Does Changing Differential Fluid Make A Difference
If your differential is in good condition and the old fluid was in good condition, then you probably won’t feel any difference after changing the fluid. But that’s not the point; the point of changing the fluid at the specified interval is to ensure the gears are always properly lubricated so the differential works properly and lasts as long as possible. It’s always better (and cheaper) to prevent than to repair, no?
Can A Bad Differential Cause Transmission Problems
It depends, but most of the time a bad differential only negatively affects the axle shafts and tires. Nevertheless, driving with a bad differential is unpleasant, causes unnecessary damage, and is potentially dangerous, so you’ll want to address it as soon as possible.
Differential Fluid Change: Final Thoughts
So, that’s pretty much everything you need to know about differential fluid changes. The last thing we want to note is how to maintain your car’s differential, which isn’t too difficult as the only maintenance you need to do is change the fluid at the specified interval.
As mentioned, this is around 50,000 miles for most cars, but check your service manual to be sure. Aside from that, just drive your car with some mechanical sympathy. Taking it easy will help maintain parts in your car. And if your car doesn’t have an underbody panel, be wary of road debris and tall speed bumps so you don’t damage the differential.
If you drive your car hard—such as taking it drifting—then pay attention to any signs of differential wear and damage. Detecting them early can help prevent expensive repair bills. And it probably won’t hurt to change the fluid more regularly.
Anyway, most car differentials can last up to 150,000 miles if maintained properly. Hopefully, this has been helpful for you. And if you’re going to change the fluid yourself, good luck!