Answers to Important Questions about Car Differential Service

Your car has an assortment of moving parts to enable motion, and most of these require service at scheduled times, depending on vehicle usage. However, many motorists don't know what the differential is and often forget to service it as required. This article outlines the importance of the differential and why it should be serviced regularly.

What does the differential do?

If you have to make a turn, your rear wheels don't travel the same distance – the left wheel goes a longer distance in a right-turn and vice versa. Therefore, the wheels must travel at different speeds to execute the turn smoothly. This is enabled by the differential – there's one at the front and another at the back – which delivers different levels of torque to the axle, allowing tyres to go at different speeds.

Why and when should the oil be changed?

Gears in the differential are immersed in differential fluid, which protects moving parts from excessive friction and the resulting heat and wear. Differential fluid is thicker than engine oil, but lighter than grease. However, high temperatures and contamination from normal driving breaks down the viscosity of the fluid and can prevent proper turning of the gears. This can cause greater damage to other parts, and even an accident during driving.

How often you change your differential fluid depends on your vehicle, anything from 65,000-90,000 miles. The differential has a fill hole, through which you can check oil levels. This can be done at your regular car service appointments, and your mechanic will tell you if the oil needs changing or refilling.

What are the symptoms of differential malfunction?

If left unattended to, you car's differentials may start to malfunction, and this happens in the following stages:

• Humming – precision is important with moving parts such as the differential gears. Low levels of fluid will cause humming from the rear because gears and pinions aren't properly greased. Boosting lubricant levels should remove the humming.
• Growling – this happens if the humming noise is ignored, and signals that the pinion and ring have sustained permanent damage and must be replaced. This is expensive and must be done by an experienced professional.
• Noises when turning – it's important to know which sounds your vehicle makes when turning so that you don't miss abnormal sounds. Differential malfunction is easy to diagnose because these noises become loudest when the car turns. If you leave them unchecked, you may ruin the entire differential, and replacement is very expensive.
• Vibration – this signals that your differential system has failed completely. Your car vibrates, fluid will leak and you'll find acceleration severely diminished. Vibration may be felt only on the floor of the car or throughout the entire car.