A differential, or gearbox, basically transfer the power from the transmission to the rear wheels and lets the wheels turn at different speeds when cornering. It is one of the most important parts of a vehicle’s powertrain. And because of that, it’s also one of the most expensive and troublesome parts to replace on a car (after the engine and the tranny). For that reason, keeping your differential in top shape is essential.
But, What Exactly Does a Differential Do?
Many individual gears work as one in the differential and they work to maintain the right tire speed when the car is driving directly down a straight roadway, but they also help adjust the speed of the wheels as the car goes around curves. For instance, when a car is going around a sharp curve in the road, the inside wheels need to go a little slower than the outside wheels. The differential, and the gears and fluid surrounding them is what ensures the wheels will turn at the speeds they need to turn to offer the car maximum stability during a drive.
The gears inside the differential are surrounded by fluids that help keep them protected while the vehicle is in operation. As a car is driven, the differential fluid heats up and over time, breaks down to a point where a car will have metal to metal contact that stops the gears from being able to turn the wheels.
The Difference in Differentials
Owners of rear-wheel-drive cars will find that their differential fluid is located at the rear of the car, which is why a mechanic will recommend having the rear end checked or having the rear end fluid changed.
Front-wheel-drive cars will have the differential in the front of the car. The difference with a FWD vehicle is that the differential lives inside the transmission and takes transmission fluid rather than separate differential fluid. It works the same, however, and still ensures the wheels turn at different speeds when needed. When a vehicle owner must get a repair shop to check their transmission fluid or change it out, they are essentially having their differential fluid checked or changed.
What about 4WD? These have differentials as well, but unlike 2WD vehicles, a 4WD has three separate differentials that include one in the front as well as another in the center and one in the back as well. The one located in the center is commonly known as the transfer case and it has a job all its own. The center differential is what fine-tunes precisely how fast or slow the speed is on the rear wheels and front wheels.
Reasons for a Change
While mileage alone can be a legitimate reason to have the differential checked or have the fluid changed, there are also other reasons that may cause a change to be necessary long before mileage even comes into play.
First, based on manufacturer’s recommendations, cars may need a regular differential service anywhere from 20,000 to 50,000 miles. This will, of course, depend on the type of car and your style of driving (highway, city, off-road, etc.). It is important to take some time to read the handbook of your car because it will tell you when different services including oil changes, transmission fluid changes or rear-end servicing need to be taken care of.
If you own a truck and do a lot of heavy hauling, it can cause those fluid temperatures to rise to levels that cause them to burn faster than they would under normal wear and tear, thus making it possible for the vehicle’s fluids need to be serviced sooner than the mileage recommendations.
How Differential Fluid is Changed
Differential fluid can be changed in various ways depending on the vehicle as well as the tools the repair shop has on hand to drain and refill the fluid. Some of the more modern shops will possibly own an extractor that will not only remove the old fluid but will also refill with new fluid. Older shops and those who don’t own an extractor machine will often pull the drain plug and let the fluid drain out slowly and then will manually refill the fluid using a pump or an oil syringe.
The mechanic will watch for metal shavings in the old fluid and will be able to either refill immediately with new fluid if no shavings are seen or remove the cover and get everything nice and clean before refilling with new fluid. Metal shavings can cause the gears to mess up even when new fluid is put in, so taking some time to remove the cover and thoroughly clean the inside of the differential is always a must.
Most vehicle owners strive to ensure regular maintenance is taken care of. This not only includes regular oil changes or tire rotations or even brake jobs but also includes having the differential oil checked and changed when needed. Think of it this way, having your rear end checked when needed might cost you some dollars, but not showing some love to your differential and watching it die could be a lot more expensive. Save your money and keep your car running smoothly by having the differential fluid checked and changed when needed.