What is a differential?
When you turn your vehicle, the inside wheels will travel a shorter distance than the outside wheels. The differential will take the power from the driveshaft and transfer it to the wheels. Also, the differential will allow each wheel that gets power to them to turn at different speeds to account for the difference in the distance they need to travel. This is useful because if they had the same power, the wheels would start skipping or skittering.
The number of differentials and also their location depends on the type of vehicle you are looking at. For example, a front-wheel drive vehicle will only have a differential on the front axle. Also, a rear-wheel drive vehicle has a differential on the rear axle. And finally, an all-wheel drive vehicle will have three differentials. The front differential, the rear differential and a differential in the center of the transmission. Some four-wheel-drive systems or part-time full-wheel-drive systems do not have a center differential so that the front and rear wheel spin at the same rate.
If you want to learn more about differentials, check out our Diagnosing Differential by Sound article and our How Differentials Work series where we go over a wide range of topics. For example, what a differential does, locking differentials clutch-type, cone ratchet & Torsen and hydraulic locking.
Why differential maintenance is important
Differential maintenance is essential to the health of the vehicle. The differential oil lubricates the gears and can degrade. This degradation can cause the gears in the differential to grind together as the oil loses thickness over time. Also, the differential oil is important for maintaining the temperature and preventing the differential gears from overheating. The differential oil can also become contaminated over time, which depending on the type of contamination can cause various effects. Changing differential fluid regularly helps maintain the health of the differential.
Contamination of differential fluid
The differential fluid in your differential could become contaminated with different sources. This could be water, or particles getting into the oil. This could be because of worn-down seals in the ring and pinion and the differential or damaged gears causing metal particles to accumulate in the internal components. If the vent hose is damaged, it can also cause water to get into the differential. Damaged seals can also let dust in from the road or other sources, causing build-up and damage.
Water contamination is characterized by the differential oil becoming cloudy, milky color and foamy. This can cause the gears to rust, and in severe cases damaged or broken gears.
How often do you need to perform maintenance?
Generally, you should check your differential oil and do maintenance on your differential every 50,000 miles. This can vary on multiple factors, such as the vehicle you drive, driving on gravel or dirt roads often and more. The differential will be filled with gear oil which, unlike motor oil or engine oil, is thicker and motor oil needs to be changed more often. The thicker gear oil is important because of the metal-on-metal contact of the gears.
Differential maintenance steps
The first step to changing the differential fluid is to check if the filler plug can be unscrewed. This is important because you can get through a lot of the steps and just not be able to put gear oil into the fill hole.
Next, you need to determine the type of differential you have. A limited-slip differential will require an additive when you change differential fluid. Some differentials have an easily accessible differential cover and some just have a drain hole. If you have a differential cover, then you will need to get or make a new gasket for it.
You will need some specialized tools to fill the differential with differential fluid. These include:
- Torque wrench
- Socket wrench with an extension
- 1/2 inch socket
- Flathead screwdriver
- Pump and hose
- Oil drain pan
- Brake cleaner
- Plastic scraper
- Paper towel
- Gear oil
- Limited-slip differential additive, if needed
- Differential gasket or RTV silicone gasket maker (needs to say it works with rear differentials or differential covers – This is not needed if your differential just has a drain hole.
- Crush washers if needed
- Scissors or pliers to cut the silicone gasket maker applicator
Checking the differential fluid levels
Using the extension on your socket wrench, unscrew the filler plug. The filler plug in some cases is magnetic, and you will find metal on it, clean this off. Then using a finger put it in the fill hole and check the fluid level. The fluid should be right up to the edge of the fill hole.
Removing the differential cover
First, place the oil pan under the differential. Then, you will need to remove the differential cover to drain the old differential fluid. To do this, use the socket wrench with the 1/2″ socket and, except for the top bolt, remove all of the other bolts.
Next, unbolt the top middle bolt halfway, this will ensure that the cover does not fall off as you are draining the differential fluid. Then, using a flathead screwdriver, separate the cover a bit and let the old differential old drain into the oil drain pan. Then, remove the top middle bolt and remove the differential cover and let the area drain.
Before putting the differential cover back on
Now that the cover is off, it is now a good time to check the differential gears and make sure they are not damaged. It is also a good idea to clean the differential cover. To do this, wipe up the excess oil. Then, spray the inside of the differential cover with brake cleaner and wipe out the inside with a paper towel. Especially make sure the edge that connects to the main differential is as clean as possible and doesn’t have dents or scratches.
On the main differential, using a plastic scraper, scrape the edge that touches the differential cover. Then, spray brake cleaner on a paper towel and clean that edge as well, it needs to be clean so that the new seal can make proper contact without having any leaks.
Finally, apply the silicone gasket maker around the edge of the differential cover if you are unable to find a gasket for your differential. You are aiming to have one continuous bead of silicone around the entire cover. Also, the silicone should be in the center of the area.
Putting the cover back on
First, put the differential cover back on using the top and bottom middle bolts and hand tighten the bolts. Then, in a star pattern hand tighten the rest of the bolts, you do not want the bolts to be tight yet. Let the silicone set for an hour. After the hour is done, tighten the bolts in a star pattern again to around half of your required torque, usually around 25-35 ft-lbs of torque. Then, in a star pattern tighten the bolts the rest of the way. Using the square end of a socket, remove the fill bolt.
Vehicles without a differential cover
Some vehicles do not have a differential cover but instead, have a drain hole. For these vehicles, remove the bolt on the fill hole first with the square end of the socket or the socket extension. Then put an oil drain pan under the drain hole and remove the drain bolt the same way you removed the ill bolt. If you have jacked up the vehicle to get access to the differential, you may need to lower the vehicle to get it level so it drains properly. This is also a good time to replace any washers that are on the fill or drain bolts.
Before filling the rear differential or front differential, make sure you install the drain bolt back in. This will need to be installed using a torque wrench. How much pressure you need to use to put the bolt back in is different between vehicles, somewhere between 25 and 35 ft-lbs of torque.
Filling the differential
Make sure you are using the right gear oil in your differential. First, make sure the oil drain pan is under the differential. Then, using the pump, put the hose into the fill hole of the differential and pump the oil into the differential just until you see the liquid start to come out of the fill hole. You will need to make the vehicle level before putting the fill bolt back in. Using the extension for the socket on your torque wrench, tighten the fill bolt to your vehicle’s required torque, around 25-35 ft-lbs of torque.
How we can help
At Houston Rebuilt Axles, our team is made up of experts in axle and differential repair. We work on rear differentials, front differentials, axles and more. We can also modify a differential or axle for any purpose. Our team is here to help you with any differential rebuild or repair needs that you may have. We can also take care of any differential oil issues you may have in your rear differential. Contact us today and our experts will be glad to help!