How To Fix a Differential Leak

mechanic fixing car's differential leak

 If you've been hearing a whirring or clicking noise coming from the back end of your car, there's a good chance that there will be a rear differential repair in your near future.

In some cases, you won't hear any noises at all, but there may be a noticeable leak. A differential leak is nothing to ignore. Without the necessary oil keeping the metal gears lubricated, they'll grind up against each other, causing extensive damage.

In this article, we're going to teach you about your differentials, how they work, and what to do if they start leaking. Keep reading to learn more.

A Crash Course in Differentials

Don't worry, you don't have to be a mechanic to understand the moving parts of your vehicle. But knowing the basics will save you a lot of time and money as your car ages. Those basics always start with your owner's manual. Each vehicle comes with one, and it usually includes a servicing schedule so you know when to take your car in for things like a tune-up, oil changes, etc. 

Keeping up with these scheduled services is crucial because it will help you avoid costly repairs. To give you some perspective, a rear differential replacement can cost upwards of $1200, which can easily be avoided by simple, scheduled maintenance. 

Now, on to your differentials. Your differentials are the last thing that stands between your engine's power output and the physics of how your wheels turn. This makes the purpose of your differentials to shift the direction of this power.

Why is this important? Because it allows your wheels to gain independent movement from each other and rotate at different speeds. For example, when you make a right turn, your front driver's side wheel must turn faster than the front passenger's side wheel.

Without differentials, your wheels can't travel at their own independent speeds. This will cause your wheels to slip and slide as you try to make turns. It's very inefficient and very dangerous. 

Causes of a Differential Leak

Now that you have some basic differential knowledge under your belt, it's important to understand the causes of a differential leak. If you recall, we mentioned that your differential housing contains gears and gaskets—which need to be lubricated. 

Considering all the components that make up your differentials, the causes of the leak could be from any (or all) of the following:

  • The Differential Gasket which is a rubber or silicone seal that wears down over time
  • The Differential Pinion Seal which is located around the yolk that attaches to the driveshaft at the front of the differential. This seal is made up rubber, which also wears down over time
  • The Differential Side Seals which are also made of rubber and keep the differential fluid from leaking onto your brakes. These also wear down over time, causing a differential leak

If you notice that you have a differential leak, you'll want to take action as soon as possible, especially if that leak is a noticeable puddle underneath your differential. 

Fixing a Differential Leak

While fixing a differential leak isn't all that complicated, it will be difficult if you're not mechanically inclined. If you have no idea what you're doing, take your car to a trusted mechanic. For everyone else who knows their way around a toolbox and an auto parts shop, here are the steps to fixing your differential leak:

Note: these steps are for fixing a rear differential leak, as the process for front differential leak repairs is different since they're attached to your vehicle's transmission.

Step #1

Assemble your tools and parts, and make sure you have about three to five hours to complete the job. The tools you'll need include:

  • A jack and stands
  • A can of brake cleaner
  • Flathead and Philips head screwdrivers
  • A ratchet and socket set
  • A gasket scraper
  • A torque wrench
  • A drip pan
  • Limited-slip additive (if you have a limited-slip differential)
  • The replacement gaskets and gasket silicone
  • Differential fluid
  • rags
  • RTV silicone*

*RTV silicone isn't 100 percent necessary, but it's recommended to add as a gasket adhesive.

Step #2

Jack up your vehicle's rear end just enough to give yourself the clearance to work. Set your drip pan down underneath the differential housing, and locate the fill hole plug. 

Step #3

Remove and inspect the fill hole plug. These plugs are magnetized, so it'll probably come out with metal shavings attached. The amount of metal shavings you see will indicate how worn down the gears are, giving you an idea of how worn down your differential is. 

Step #4

Now remove the housing bolts, starting from the top left and working your way over to the top right. Leave the top center bolt for last. When you get to the top center bolt, only loosen it halfway.

Step #5

Carefully pry off the housing cover with a flathead screwdriver. Allow the fluid to drain completely before removing the top center bolt and housing completely. Once you do this, you can begin cleaning the housing covers. 

To clean the housing covers, use the can of brake cleaner to spray the cover and wipe thoroughly with your shop rags. Be sure to remove any hint of residue. Then take your gasket scraper and scrape off the old gasket.

This process should result in a clean and flat housing cover. If there's any damage, you'll need to replace it. 

You'll also have to clean the housing itself. You can use the brake cleaner for this as well, just don't spray it directly onto the gears! (Spray it onto the rag first).

Step #6

Prep and install your new gaskets. If you are using the RTV silicone to help seal your gaskets or create a new gasket, be sure to follow the directions and let it sit for about 15 minutes before putting the housing cover back on.

Step #7

To put the housing cover back on, insert the top and bottom bolts to the cover before putting the cover back on the housing. Tighten those bolts by hand, and then add the rest of the bolts—tightening them all by hand.

Then refer to your service manual for the amount of torque needed and torque the bolts accordingly.

*if you've used the RTV silicone to create a seal, you'll want to apply and tighten the bolts in a start-pattern until it begins to push through.

Step #8

Fill your differential with new fluid. You'll find the amount needed in your owner's manual. Once it's filled, you can re-install the (clean) fill hole plug and torque it to specs. Be sure to wipe up any excess gear oil on the outside.

Once all if said and done, you can remove the jack stands and lower your vehicle back to the ground. 

Keep Up the Good Work

Now you have a basic understanding of how differentials work and how to spot and fix a differential leak. Remember, if you don't feel confident enough to do the job yourself, just head over to your mechanic.

For more how-to advice on cars or life in general, check back with us daily. 


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