6 Causes of a Differential Leak & How to Fix Them

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differential stop leak

If your car is leaking fluid from the rear differential, you’re not alone. The rear differential leak is also one of the most common problems of the 2005-2014 S197 Ford Mustang face after 100,000 miles. 

This is a common issue that many car owners experience at some point. Several things can cause a rear differential leak, and it’s important to determine the root of the problem so you can fix it.

This article will discuss what causes rear differential leaks and how to fix them. We will also review some of the best products on the market to stop these leaks. Finally, we will cover the cost of fixing a rear differential seal leak and answer some frequently asked questions about this topic.

What is a Rear Differential?

A rear differential is an important component in most types of vehicles. This part helps keep the drive wheels spinning at different speeds when you drive straight and turn corners, preventing the vehicle from becoming stuck to one wheel while it rotates more quickly than another.

The differential is also very helpful during slippery weather conditions, helping your car gain more traction and grip. It can be difficult to drive without a working differential, so it’s important to keep yours in good condition and get any necessary repairs done as soon as possible.

Where is Rear Differential Located?

The rear differential is typically located within the back of the vehicle, next to the driveshaft, and between the rear axle housing. There are several different types of differentials, but most work in a similar way.

The differential contains a set of gears that are connected to the driveshaft. These gears rotate when you turn the steering wheel and allow the drive wheels to spin at different speeds. This action helps keep your vehicle moving forward smoothly, even when you’re making turns.

What are the Main Causes of a Rear Differential Leak?

Following parts of a differential can develop a leak. If you suspect that differential fluid is leaking from under your car, then look out for these:

  1. Bad Differential Gaskets
  2. Rear Differential Pinion Seals
  3. Damaged Differential Cover
  4. Bad Differential Side Seals
  5. Leaks in Differential Tubes
  6. Worn Axle Seal

Let us take a closer look at each of these problems and how to fix them as well:

1. Bad Differential Gasket:

The main function of the differential gasket is to provide a seal between the differential case and the differential cover. If this gasket becomes damaged or worn over time, it may cause leaks in your differential. Unfortunately, if this happens, you will have no choice but to replace the gasket entirely to fix the leak.

2. Rear Differential Pinion Seal:

The pinion seal is located at the rear of the differential and is responsible for sealing the area where the driveshaft enters the differential. Over time, this seal can become damaged or worn, which will cause a leak in your differential. If you suspect that this seal is leaking, you should replace it as soon as possible to prevent further damage.

3. Damaged Differential Cover:

The differential cover is there to protect the internal components of your differential from damage and water entry. If this cover is damaged or cracked, it can result in leaks or other problems with your differential. The main reasons why a differential cover may get damaged are due to impact (such as a rock hitting it while driving) or due to corrosion. You may need to replace the entire cover if it cannot be repaired to fix this issue.

4. Bad Differential Side Seals:

The side seals are located on each side of the differential, and their main purpose is to seal the bearings in place. These seals can become damaged or worn over time which will cause a leak in your differential. If you suspect that your side seals are leaking, you should replace them as soon as possible to prevent further damage.

5. Leaks in Differential Tubes:

Differential tubes are responsible for carrying the differential fluid from the differential to the axle. It is important to carry differential fluid from the differential to the axle because if the differential fluid level gets too low around moving parts of the axle, it can cause damage. Differential tubes can develop leaks over time which will cause a loss in the differential fluid. If you notice that your differential fluid level is low or if you see a leak coming from your differential tubes, you should replace them as soon as possible.

6. Worn Axle Seal:

The axle seal is located at the end of the axle, where it meets the differential. This seal helps to keep the differential fluid from leaking out of the axle. Over time, this seal can become worn or damaged, which will cause a leak in your differential. If you notice that your axle seal is leaking, you should replace it as soon as possible to prevent further damage.

As you can see, several different parts of your differential can develop leaks over time. By knowing the causes and symptoms of differential fluid leaks, you will be able to identify and fix them quickly and easily.

How To Fix Differential Seal Leaks?

Differential seal leaks are one of the most common problems that car owners face. Although it is not a serious problem, it can be quite annoying and inconvenient, especially if it happens frequently. If you are facing this problem, you can do a few things to fix it depending upon which parts are posing the problem.

If the Problem Lies With Differential Cover or Differential Gasket:

If the problem is with a differential cover or gasket, you will have to replace them to fix the leak. This is not a difficult task and can be done quite easily if you have some basic knowledge about car maintenance.

1. Raise the vehicle and support it on jack stands.

2. Remove the axle shafts from both sides of the differential assembly if equipped with axles. If your car does not have an open differential, you will have to remove these shafts first to gain access to the rear cover bolts.

3. Drain the differential lubricant from the differential assembly.

4. Remove the rear cover bolts and remove the cover by pulling it upward or prying with a suitable pry tool, if necessary.

5. Inspect the gasket surface of the differential case for dirt, rust, or other foreign matter that might prevent sealing pressure between the case and gasket. Clean these areas with a scraper or wire brush.

6. Inspect the differential case for any damage such as worn threads, cracks, dents, and corrosion. If there is wear on the bearing journal surfaces and these areas cannot be repaired by machining, replace the differential assembly with a new one.

7. Install a new gasket to the differential case. Make sure that the gasket is positioned correctly and that all of the bolt holes align.

8. Install the rear cover to the differential case, being careful not to disturb the gasket. Torque the bolts to specification.

9. Install the axle shafts, if removed, and torque the axle nut to specification.

10. Lower the vehicle.

11. Fill the differential assembly with the proper fluid and quantity. Refer to your owner’s manual or a service manual for this information.

If the Problem Lies With Differential Pinion Seal, Differential Side Seals, and Axle Seals:

Differential pinion seals, differential side seals, and axle seals are all important components of your vehicle’s drivetrain. Each one plays a critical role in keeping the Differential fluid where it belongs and prevents leaks.

Over time, these seals can wear out or become damaged, causing leaks. If you notice any fluid leaks coming from your vehicle’s Differential, it is important to replace these seals and keep your vehicle safe. You may do so by following the procedure below:

1. First, locate the Differential’s fill plug on the side of the differential housing. With the engine off, remove the fill plug with a socket or wrench.

2. Next, using a drain pan, drain the Differential fluid into it. You may need to use a funnel to ensure that all fluid is drained.

3. Once the Differential is drained, remove the old pinion seal by prying it out with a screwdriver or another appropriate tool. Be careful not to damage the differential housing when removing the old seal.

4. To install the new pinion seal, lubricate the seal lip with Differential fluid and press the seal into the differential housing.

5. Next, install the new Differential side or axle seals by pressing them into the differential housing with a seal installer tool. To do so, you may need to tap the tool with a hammer until it is fully seated in the differential housing.

6. After installing all-new Differential pinion seals, differential side seals, and axle seals, fill the Differential with fresh oil.

7. Finally, replace the fill plug and run your vehicle to check for any leaks from the new Differential seals. If you notice any leaks, repeat the procedure until all of them are fixed.

How To Prevent Differential Seal Leaks?

One of the most common problems that you may encounter with your differential is a leak. Leaks can be caused by various factors, including wear and tear, damage from debris, or rust. If not properly addressed, these leaks can lead to serious problems for your differential, such as reduced performance and damaged components.

Fortunately, there are simple steps that you can take to help prevent a rear diff leak. Below are some tips for preventing these leaks and keeping your differential in good working order:

1. Check the fluid level regularly:

One of the most common causes of differential seal leaks is low or dirty fluid. Checking the fluids on a regular basis will help to ensure that they are at an optimal level and can help to catch any engine leak or differential leaks before they become serious.

2. Keep the area around the differential clean:

Debris and dirt can cause wear and tear on the seals, leading to leaks. Keeping the area around your differential clean will help reduce the chances of this happening.

3. Inspect the seals regularly:

Over time, seals can become worn and damaged. Inspecting the seals regularly will help to identify any potential problems before they become serious.

4. Regularly schedule maintenance appointments:

Having your differential regularly serviced by a professional mechanic can help prevent leaks and other problems from occurring. This may involve flushing or replacing the fluid or replacing worn or damaged parts.

5. Use quality fluids and parts:

Using high-quality transmission fluid and replacement parts can help to extend the life of your differential and reduce the chances of leaks occurring. This will also enhance overall performance, making your vehicle more efficient on the road.

Rear Differential Leak Fixing Cost

If you have a rear differential leak, it is important to get it fixed as soon as possible. Depending on the severity of the leak, it can cause damage to your vehicle and even make it undrivable. The average cost for a rear differential leak repair is between $150 and $2,000. This is a huge bracket, but fixing the cost would depend upon the fact which part or parts have gone bad. Let us see that in detail:

If You’ve Bad Differential Gasket:

The average cost for a differential gasket replacement is between $350 and $450. Labor costs are estimated between $167 and $211, while parts are priced between $183 and $239. This range does not include taxes and fees and assumes that both the front and rear differential gaskets will need to be replaced simultaneously.

If You’ve Bad Rear Differential Pinion Seals, Side Seals, or Axle Seals:

The average cost for a Differential Pinion Seal Replacement is between $184 and $217. Labor costs are estimated between $109 and $189, while parts are priced between $20 and 40. However, the exact cost may differ depending on the make and model of your car. Fixing axle seal leak or rear main seals replacement cost will be added if they are damaged. Therefore, it is necessary to get the replacements done immediately.

If You’ve Damaged Differential Cover:

Differential covers aren’t the most expensive part of your car, but they’re not cheap either. Depending on the make and model of your vehicle, you can expect to pay anywhere from $100 to $300 for a new differential cover. That said, the cost of replacement will vary depending on the severity of the damage and whether or not you need to replace any other parts while you’re at it.

If the Entire Differential is Gone Bad:

The cost of replacing a car differential will vary depending on the make and model of your vehicle. Most diffs will need to be professionally installed so that the labor costs can add up quickly. The parts themselves are not cheap either, so expect to pay somewhere between $1,000 to $2,000 for most rear-wheel drive vehicles.


A rear differential leak can be a serious problem that can lead to expensive repairs. However, there are some things that you can do to prevent leaks from happening in the first place. These include: checking the fluids regularly, keeping the area around the differential clean, inspecting the seals regularly, and scheduling regular maintenance appointments. If a leak does occur, it is important to get it fixed as soon as possible to avoid further damage.

Differential problems can be difficult to diagnose and repair, so it’s always best to leave this type of work to a professional. A mechanic will be able to thoroughly inspect your vehicle and make any necessary repairs so you can get back on the road safely. Whether it’s a leak or just worn-out seals, they will know exactly what needs to be done to restore your car’s drive system to good working condition.

Frequently Asked Questions

What are the major symptoms of a rear differential leaking seal?

There are a few major symptoms of a rear differential leaking seal.

1. Whining Noise:

Your car will make a whining noise when you accelerate. This is because the gears are not properly lubricated and are grinding against each other. Another symptom is that your car will vibrate when you drive at high speeds. This is because the differential cannot spin at the same speed as the wheels.

2. Leaking Fluid:

If you see fluid leaking from the back of your car, it is most likely differential fluid. Differential fluid is a thick, dark green or red fluid that smells like burnt gear oil. If you see this leaking from your car, it is important to get it fixed as soon as possible, as it can damage your car’s differential.

3. Burning Smell:

If you smell something burning while driving, it could be the differential fluid overheating. This is caused by the gears not being properly lubricated and can damage your car’s differential.

If you notice any of these symptoms, it is important to take your car to a mechanic and have the rear differential seal replaced.

What is a differential stop leak?

Differential stop leak is a great way to prevent costly repairs and extend the life of your vehicle’s differential. Differential stop leak is a type of additive that is used to help seal small leaks that occur in the differential component of your vehicle.

Differential stop leaks can be purchased at most automotive stores and online. It works by chemically reacting with the fluid in your differential, helping to seal minor cracks and prevent further leaking.

There are many brands of differential stop leak available, and they vary in price. Most are safe to use and, if used properly can prolong the life of your vehicle’s differential or even prevent any damage from occurring.

What are some of the best differential oil stop leaks on the market?

Following are some of the best differential oil stop leak products available:

• BlueDevil Rear Differential Sealer

• Lucas Oil Heavy Duty Gear Oil

• Royal Purple Max-Gear Synthetic Gear Oil

• Red Line 75W90NS gear oil

Each of these products is designed to help seal minor leaks and prevent further damage.

Can differential stop leaks fix oil leaks from axle seal?

Differential stop leaks can help fix oil leaks from axle seals, but they will not completely eliminate the leak. To get the best results, it is important to follow the directions on the product label and apply the sealant evenly around the seal.

Is it okay to drive if engine oil or gear oil is leaking?

It is not advisable to drive if engine oil or gear oil is leaking. This could potentially cause serious damage to your vehicle. If you must drive, be sure to keep an eye on your oil levels and top off as needed. You may also want to get the leak fixed as soon as possible to avoid further damage. If you experience any difficulties while driving, pull over and call a tow truck to help you out.

Can you slow down an oil leak?

The differential is responsible for distributing power to the wheels, and an oil leak can cause it to work less efficiently. You can slow down an oil leak in your car’s differential by adding a sealant to the area around the leak. This will help to temporarily stop the flow of oil until you can get the car to a mechanic.

Is it safe to drive if differential fluid is leaking from the rear pinion seal?

There is no definitive answer to this question since it depends on the severity of the leak and other factors. In general, however, it is usually safe to drive if there is only a small amount of fluid leaking from the pinion seal. If the leak is significant or your vehicle has not been regularly maintained, you may need to have the differential fluid replaced more frequently.

After how long does the rear differential develop a leak?

Several different factors can contribute to the development of a leak in the rear differential. Some of these factors include age, mileage, and driving conditions. If your vehicle is more than ten years old or has over 150,000 miles on it, you may start to experience leaks from around the rear differential seal.

Additionally, suppose the differential is exposed to extreme heat, such as in an off-road or racing car with poor ventilation. In that case, the differential seal may become damaged and leak. Driving conditions can also influence the development of a rear differential leak.

If you frequently tow heavy loads behind your vehicle, this can put extra strain on the ring gear bearings and lead to leaks.

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