Rear Differential Leak – Causes and How to Fix the Leak

Don’t be like many religious car owners in changing their engine oil and transmission fluid but don’t pay any attention to their rear differential fluid until it leaks. Today, I’ll discuss rear differential leak – causes and how to fix the leaking.

Differential leaks usually come from the rear differential cover, the pinion seal attached to the drive shaft, or the axle seals. If there is grayish or light brown fluid on the garage floor beneath the back of your truck, then that would indicate your differential fluid is leaking.

There are several reasons why your vehicle’s rear differential is leaking, including a damaged differential gasket, a bad differential side seal, or a leaking pinion seal. You need to have this leak fixed as soon as possible because it can lead to differential gear damages, which are more expensive to repair.

Read on to learn more about rear differential leaks, their causes, and possible fixes.

Rear Differential Leak

rear differential leak

Can Come from the Pinion Seal

The rear differential leaks of your vehicle could occur in some of its parts. Rear differential leaking can come from the pinion seal, where it is connected to the driveshaft. But it could also come from the rear differential cover or at the axle seals.

Tiny Pool of Grayish or Light Brown Liquid

You have to suspect that it is a rear differential leak if you notice a tiny pool of grayish or light brown fluid on the pavement beneath the back of your truck. You need to have this leak fixed right away before it leads to more severe damage to the differential.

Causes of Differential Leaks

There are several causes of differential leaks:

  • Damaged differential gasket,
  • Bad differential side seal, and
  • Leaking pinion seal.

If any of these differential components break down, the differential fluid will run low, putting the differential components at risk.

Strange Noises from the Car’s Back

If you hear strange noises coming from the back of your car, the problem has gone bad. You are facing an expensive rear differential repair. Don’t let the problem go this far. Be aware of fluid leaks, especially fluid oil leaks, at the back of your car.

How Important Is the Rear Differential?

Transfers Engine’s Power to the Rear Wheels

The rear differential performs an important role in the efficient operation of your car. It has a set of mechanisms that are connected to the driveshaft. Also, the rear differential transfers the engine’s power to the rear wheels of your car.

Changes the Direction of Power

Its role is really very simple. The rear differential changes the direction of the power delivered by the engine from longitudinal to rotational power. This longitudinal power running along the car is changed into rotational power directed to the rear wheels. In that way, the rear wheels rotate.

For Rear-wheel-drive Cars

The transmission delivers power through the driveshaft in rear-wheel-drive cars. This driveshaft then delivers the power input into the differential. Inside the differential, the power input is split into two shafts. These two shafts are called axles that supply the power to the two rear wheels.

For 4-wheel Drives

For 4-wheel drives, the transfer case after the transmission divides the power delivered by the engine into the front and the rear driveshaft. Each of these shafts provides power to their respective differentials.

Enable the Car to Maintain Its Balance

The primary function of the rear differential is to enable your car to maintain its balance when it is making a turn. It makes the outside wheels rotate faster than the inner wheels. So, the faster speed of one wheel is balanced by the slower speed of the other wheel.

More on Rear Differential

rear differential leak fix

Differential Location

For vehicles with rear-wheel drives, the differential is located at the rear. You can find inside the differential housing a thick dark fluid that acts as the lubricant of the differential gears. For front-wheel drive vehicles, the differential is usually a part of the transmission housing. It uses the same fluid used by the transmission.

Rings and Pinion Gears

Also found inside the differential housings are ring and pinion gears. They transfer power from the driveshaft to the rear wheel axle. The differential fluid lubricates these parts of the differential. Any leak of this differential fluid will damage these parts severely.

Causes of Differential Leaks

So, if you notice traces of oil underneath your car directly under the differential, you have to know why it is there. If you don’t have enough fluid in the differential, your car will not run smoothly. But why will this fluid leak from the differential?

There are many possible reasons for a leaking rear differential:

1. Bad Differential Gasket

This gasket is usually made of rubber or silicon. Over time, this gasket will wear out. You can expect differential fluid leaks from the differential casing when it does.

2. Bad Differential Side Seals

These seals prevent the fluid from the differential from leaking into the brakes. They are also made of rubber or silicon and can deteriorate or damage over time. When they do, you will experience differential fluid leaks.

3. Differential Pinion Seal

The pinion seal is located around the yoke. This yoke is at the front of the differential and is attached to the driveshaft. It is also made of rubber or silicone. Over time, it can be damaged and develop a leak.

Again, what is a rear differential leak? The possible causes of rear differential leaks include issues at the axle seals, the pinion seal, or the cover. The presence of light brown or grayish leaks on the ground signifies a differential leak.

How to Fix Differential Leaks

If you discover fluid leaks in your differential, it is not the end of your rear differential. However, fixing this kind of problem is not usually a DIY project. Professional mechanics usually perform them. Here are the steps:

1. Reseal the Sides

When a differential fluid dripped onto the rear brakes, the sides of the differential could be leaking. Fixing this problem is time-consuming. You will have to remove the axle shafts. And then you need to remove the damaged seals and replace them with new ones. After doing all this, you need to reinstall everything you have removed before.

2. Replace the Pinion Seal

When the transmission fluid leaks, you should replace the rear differential with a bad pinion seal. The differential has a yoke at its front side. A seal surrounds this yoke that wears out over time.

To replace the seal, you need to remove this yoke, after which you can then pry out the seal. Replace the broken seal with a new one and reinstall the yoke to its former place.

3. Replace the Rear Differential Housing or Cover

The rear differential could also give way due to wear and tear. If that happens, there will be fluids leaking from it. The only way to stop the leak is to replace the damaged cover. This cover is either made of silicone or rubber. So it will be easy to replace it with a new one. You should clean first the sealing surface before installing a new seal cover.

4. Use a Differential Leak Sealer

If you want the easiest way to seal a rear differential leak, using a differential leak sealer is your way to go. You don’t even have to search where the leak is coming from. If it does its job well, this leak sealer could put this leaking problem behind your back.

The only thing you need to do is add this leak sealer to the differential fluid. Open the oil fill plug and pour it in. You can choose from several leak sealers available online or any brick and mortar store. Just choose a high-quality one.

What If the Problem Is Bigger Than Expected?

rear differential leaking from breather
Pinion Bearing

Pray that a bigger problem does not cause the leak issue because if it is, you have to call a professional mechanic to fix the leak. In that case, prepare to pay for labor, parts, and materials required. What are these other bigger problems?

1. Damaged Rear Differential Gears

When the teeth of the rear differential gears are worn out or chipped due to lack of lubrication or old age, you need to replace them. These are very costly rear differential components. But you still have to replace them if the damage is serious.

2. Bad Pinion Bearing and Side Bearings

These rear differential parts can also develop pits over time. They can also wear out after long use. Lack of lubrication is also a culprit. Whatever the case, if these bearings are already out of their wits, you have to get a new one.

3. Entire Rear Differential Has Gone Bad

If your car’s gears fail and you can’t repair them, it’s time to replace the entire rear differential. That includes the seals, bearings, gears, and housing.

Cost of Fixing Rear Differential Leaks

On average, it is not expensive to fix rear differential leaks. The typical cost of this kind of repair can run between $200 and $400. This will already include labor and materials. Most repairs will only take a couple of hours to perform.

If the differential gears require repairing, the cost will jump significantly. For instance, if you need new gear, the cost can jump to $1,500 or even higher. Differential gears are the most expensive parts of rear differential assemblies.

At the higher end of the scale, if your car requires a new rear differential assembly, the project could set you back from $3,000 to $4,000. A used rear differential unit is also expensive. They go from $1,500 to $2,000, already installed.

Rear Differential Service Is Important

Schedule a Regular Rear Differential Service

If you want your rear differential to stay viable for a long time, you should schedule a regular rear differential service. Even if the whole assembly has a differential fluid, this lubricant will break down over time. It won’t provide the needed lubrication that the gears need.

Replace the Fluid Regularly

So, you have to replace the fluid regularly. If not, the pinion gear and the ring gear inside the differential casing will be damaged. They will wear out fast, develop pits or even cracks because of heat, contaminants, and lack of effective lubrication.

What Takes Place in a Rear Differential Service?

First, the mechanic will remove the rear differential cover. Then they will remove the old differential fluid from inside the housing and clean the casing of contaminants and other debris.

After that, the mechanic will reseal the cover and pour fresh transmission fluid into the housing. You can now safely drive your car from 20,000 to 40,000 miles. But you need to take your car back to the mechanic for another rear differential service.

Conclusion: Rear Differential Leak

The usual rear differential leaks come from are the axle seals, the rear differential cover, and the pinion seal attached to the drive shaft. If you see grayish or light brown fluid on the garage floor beneath the back of your truck or car, this indicates that your differential fluid is leaking.

You should have this differential leak fixed right away. If you don’t, you risk more damage to the rear differential gears, which are usually more expensive to repair.