Simply and traditionally put, the differential takes rotational input from the transmission and re-directs it out to the two tires. Although there are different configurations of components, the differential is generally the connection point between a drive shaft, connected to the transmission providing the power & a left and right axle shaft. The differential provides the same amount of torque to both the left & right tire when driving in a straight line. However, when the vehicle makes a turn, the differential provides more rotational speed to the outside tire while slowing the inside tire. This needs to happen because the outside tire in a turn has to travel a further distance than the inside tire.
Traditionally cars were real wheel drive where the power was created at the engine, transitioned through the transmission, connected to a drive shaft and then to the differential. the differential split the power out to the left and right tires. In the modern front wheel drive car, the differential is integral to the transmission, so there is no driveshaft in this configuration. In this case we refer to the transmission as a transaxle.
Signs You May Be Having a Differential Problem:
- Binding sensation or noise when turning
- Growling noise that seems to get consistently louder with speed
- Excessive tire chirp when going around corners
- Car does not move in either direction
- Noise that changes with acceleration & deceleration or on & off the gas
One of the most common differential repairs we perform in Phoenix, AZ is differential bearing replacement. Most notable by a growling noise that gets consistently louder with speed. Most people do not notice the noise because it gradually gets worse over time. It’s not till someone else who does not normally drive the car gets in the car and says, “wow, your car seams noisy”.
If bad bearings are addressed sooner rather than later, the price of the repair can be significantly lower. When you drive prolonged with bad differential bearings, the gears are etched and often times the differential housing can be damaged.
Here are some of the common terms or components associated with differentials:
- Ring Gear: Gear inside the differential that rotates parallel with the tires. Is is the “Driven Gear”
- Pinion Gear: Gear inside the differential that drives the ring gear “Driving Gear”. The pinion gear rotates perpendicular to the tires.
- Spider Gears: The smallest gears in the differential. There are typically four inside the differential. They allow the inner and outer tires to rotate at different speeds within a turn.
- Carrier: The ring gear mounts to the carrier and the spider gears are housed inside the carrier.
- Posi-traction: There are many types of posi-traction some more abrupt than others. It is usually used in vehicles that drive in lower traction situations where optimal traction is required. Posi-traction is generally less friendly on creature comfort and can negatively affect handling of a vehicle, however some prefer it when traction is there primary concern.
- Axle Shaft: Connected to the spider gears at the differential and the wheel and tire at the other end.
Quick type lube shops in Phoenix, AZ are fairly consistent in recommending differential service. However, we all change engine oil, but all don’t want to spend the money on differential service. If you tow or off road through wet creeks you differentials should be serviced much more frequently, maybe as much as every 10 – 15k miles. Otherwise, as a rule of thumb, differentials are typically serviced every 30 – 50k miles.
Things to be aware of when servicing your differential:
- Differentials are now requiring special type fluids based on different vehicle manufacturer. Be aware of fits all oils, they may not be what you need – your always safe with “factory fill”.
- Posi-Traction additives: There are several different types of posi-traction configurations. Not all shops take the time to make sure you get the right posi-traction additive for your differential. “This is Imperative”.
- Some differentials give you the ability to remove a cover and clean the inside of the differential housing, which we recommend. some shops simply suck the fluid out through the fill hole then pump fluid back in. It may be cheaper, but you get what you pay for.
- Differential work can be expensive; don’t be diligent spending money for differential service when it might not be performed in the right fashion. Most people don’t realize that “improper maintenance” is “worse than no maintenance” at all.
A differential is a device, usually but not necessarily employing gears, capable of transmitting torque and rotation through three shafts, almost always used in one of two ways: in one way, it receives one input and provides two outputs—this is found in most automobiles—and in the other way, it combines two inputs to create an output that is the sum, difference, or average, of the inputs.
In automobiles and other wheeled vehicles, the differential allows each of the driving roadwheels to rotate at different speeds, while for most vehicles supplying equal torque to each of them.
A vehicle's wheels rotate at different speeds, mainly when turning corners. The differential is designed to drive a pair of wheels with equal torque while allowing them to rotate at different speeds. In vehicles without a differential, such as karts, both driving wheels are forced to rotate at the same speed, usually on a common axle driven by a simple chain-drive mechanism. When cornering, the inner wheel needs to travel a shorter distance than the outer wheel, so with no differential, the result is the inner wheel spinning and/or the outer wheel dragging, and this results in difficult and unpredictable handling, damage to tires and roads, and strain on (or possible failure of) the entire drivetrain.