Proper Car Differential Maintenance: Car Owner's Guide

Educational

Oct 06th, 2021

Proper Car Differential Maintenance: Car Owner's Guide

A smooth-running vehicle causes minimal strain on the engine and other components, whilst a neglected vehicle will hamper your ability to drive. But you already know that.

What you may be forgetting is check on your car differential. It’s critical for optimum performance, longevity, and the safety of your car, so there shouldn’t be a reason to forget about it or forego proper maintenance.

If you do, you’re increasing the risk of severely damaging not only the engine but also other car parts.

How Often Should a Differential Be Serviced?

Most car manufacturers recommend changing your rear diff fluid every 48,000-96,000 km (30,000-60,000 miles). In case your differential shares housing with a manual transaxle, then you will need servicing after every 40,000-48,000 km (25,000-30,000 miles).

However, these are general guides. In practice, the frequency of changing differential fluid depends on the model of the car, driving conditions, and the quality of the differential fluid. 

For instance, you will not need to change the differential oil if you regularly drive your truck on a highway and do so under temperate conditions with minimal hauling or towing.

Conversely, if you frequently tow a trailer or haul goods under fluctuating temperature, then you will need to change the fluid more often.

The dealer can help you establish the frequency of differential servicing. Alternatively, you can skim through your car's manual for details.

Why the varying differential oil change interval?

Note that extreme operating conditions break up your car differential fluid more quickly. More so, it places tremendous stress on the bearing and gear, bringing about wear to these components.

Interestingly, manufacturers are continuously increasing the towing capacity of trucks, but they seem to be not as keen on increasing the differential fluid capacity. As a result, the stress on the differentials is higher in current models compared to their predecessors.

An ideal example is the 1996 Ford F-250 Crew Cab versus the 2017 version. The 1996 model came with a towing capacity of 4,700 kg (10,500 lb) with its rear differentials holding 3.5L (3.75 qt) of lube. On the other hand, the latter model allowed for 6,800 kg (15,000 lb) towing capacity with 3.5L of gear oil in the rear differentials.

As you can see, the same amount of fluid protects the vehicle against more heat and stress caused by increased towing capacity.

High temperatures result in a cycle known as thermal runaway. In this case, low-quality gear lube loses shear stability and viscosity. Next, the weakened lubricant results in metal-to-metal contact, causing gear and bearing failure.

What happens if you don’t change the differential fluid?

Changing the differential fluid is as necessary as changing gear oil. Proper differential maintenance prevents friction between metallic components which safeguards your car’s gear. A healthy gear means a healthy vehicle and minimal expenditure on repairs.

How to Change Differential Fluid

Drive your car for some minutes to warm the fluid. Dress appropriately because the job can be messy. 

You will need a wide-catch pan, whether the vehicle has a drain plug or not. A plastic drop cloth beneath the pan would be perfect. 

How do you change differential fluid? Step by step 

  1. Remove the fill-hole plug at the top of the differential casing.
  2. Unscrew the drain plug. Alternatively, unscrew the housing bolts if there is no drain plug. Remember to leave a few loose bolts to hold the cover in place.
  3. Open the cover using a screwdriver. Be gentle. You do not want the foul-smelling old diff oil on your face, right?
  4. Allow the oil to drain. Remove the cover.
  5. Wipe any oil that remains on the gear, lid, and the wet part of the housing cover.
  6. Clean the fill-hole plug (most types come with a magnet which grabs tiny metallic particles). 
  7. Clean the housing cover with a light abrasive pad or razor scraper, then wipe using a lint-free towel and brake cleaner.
  8. If your car lacks a pre-made gasket, use one designed for oil exposure and harsh conditions.
  9. Lay one bead on the matting side of the cover. Draw a circle around the mounting holes. Then, bolt the cover in place. Make sure you apply a considerable clamping force to flatten the bead. Allow it to harden. Next, tighten the bolts using a torque wrench.
  10. Fill the differential with high-quality oil. You can fill right from the bottle, but a pump or extension hose will be more convenient.

Note that most differentials hold up to 3 quarts of diff fluid, but you can confirm the capacity and the weight from the manufacturer’s manual. Also, some vehicles have limited-slip differentials that need a secondary friction-modifying additive.

The maximum fill-line is the bottom of the plughole. When the oil starts dripping, then you are good to go.

Lastly, put in the plug. Job completed!

What are the signs of bad differential fluid or low differential oil level?

One of the most common symptoms of bad differential oil or low differential oil level is a noisy transmission or differential. Continuous use of the car results in dirty or low levels of lubricant, which manifests as howls and whines from the gear area—the sound results from increased friction between the metallic components. Also, the volume may increase as you accelerate.

Besides the howling and whining of the gear, you should also check your maintenance schedule. Once due, you need to have a qualified technician check on your car differential.

Find Useful Tips & Tools from Carpart.com.au

If you’re handy around your workshop, you may also use the previously mentioned DIY procedure to change the differential lubricant. Take note that the process is easier for a small truck than it is for a car. 

For more tips, check out our car maintenance guides and informational blogs. And while at it, you can make use of our Car Part Finder to help you locate auto parts for your DIY needs.