The rear differential is extremely important when it comes to the proper overall function of your vehicle.
This component enables torque to be generated through the vehicle’s crankshaft and on to the wheels. Problems with the rear differential are quite rare, but if you are unlucky, you may have a damaged differential.
Here is an article on how to diagnose problems related to the rear differential and how much it will cost to repair or replace it.
Diagnosing a rear differential issue
Many people struggle with diagnosing problems related to the rear differential and have difficulty deciding whether the problem is actually a bad wheel bearing or a bad differential.
Even I still struggle with it after many years of diagnosing such problems.
This is how I usually proceed when diagnosing rear differential problems.
Lift up your car on jack stands
The first thing you should do is to lift your car on jack stands using a floor jack (or car lift). Lift both rear wheels of your car and make sure that your transmission is in neutral.
1. Turn one wheel slowly
Check if the other wheel turns in a backward direction to the wheel you are turning. This may vary depending on the type of differential your car has, but most cars use an open differential, and in this case, one wheel should turn backward when the other turns forward.
2. Let a friend hold one wheel or put one wheel down on the ground
If your car has a normal open differential and your car’s transmission is in neutral, you should be able to turn the wheel freely. If both wheels spin while you turn the other wheel, you may have a problem in the differential.
3. Start the engine and put it in gear
If your car is equipped with an ABS/ESP system, you must first deactivate it, usually by pressing a button in the car. Let the car idle, then put it in gear. Make sure that the jack stands are placed securely under your car. Without jack stands you never want to go under your car!
Keep your arms away from drive shafts, wheels and other rotating parts. Listen carefully if you can hear noise from the differential. Normally the differential should be very quiet, and if you hear a howling sound, it is most likely damaged.
At the same time, you can listen for noises coming from the wheels. This could be due to a bad wheel bearing rather than a bad rear axle differential.
4. Check the differential fluid
Pour out the differential fluid and check for signs of metal parts inside. In older cars that have not had a fluid replacement for many years, you may find a small number of metal parts; this is not unusual.
If the fluid looks good, you can top it up with the old fluid, and if it is dirty or black, replace it. Check with your manufacturer which oil you should use for the differential.
Rear differential vs Wheel bearing noise
If you can’t find any noises or metal parts in the differential, it could actually be a bad wheel bearing instead of a bad rear axle differential. The process of diagnosis can be either simple or advanced, depending on the problem.
Take your car for a ride
Drive your car on an empty road at up to 80 km/h or 50 mph. You may hear a howling noise from the rear of the car at this point.
Turn the steering wheel slightly to the left and right. If the howling noise changes in frequency, you may have a bad wheel bearing. For example, if you turn right and the noise gets higher, the left wheel bearing is most likely the problem and vice versa.
This is because when you turn the car, all the weight is shifted to the opposite side, which puts much more stress on the damaged wheel bearing and makes it louder.
If the noise does not change frequency or level when you steer the car at higher speeds, the problem is most likely with your differential or gearbox.
Have a passenger sit in the rear seats and let him or her decide whether the problem is coming from the front or the rear to determine whether the problem is in the transmission or the differential.
Prevent issues with the rear differential
There are actually not many things you can do to prevent problems with the rear differential. It’s a very compact part, so you can’t do much maintenance with it. But there are two things you should know about rear differential maintenance.
- Replace the differential fluid at the right time. Check with the manufacturer or in your maintenance documentation when you need to replace the differential fluid. Many differential fluids should never be replaced, according to the manufacturer, but there’s no harm in asking.
- Make sure your differential has no leaks. By checking the differential cover and axles for leaks, you can be sure that the level of the differential is good. A differential that has no leaks should never have too little fluid. However, sometimes the differential fluid can leak through the axles, so you must make sure that there is no fluid in the rear brakes. You can also check the differential level with the level plug. Refer to your repair manual to find the level plug. A low fluid level in the differential can cause serious damage to your differential.
Rear Differential Repair or Replacement Cost
If you have checked the above guide and decided that the problem must be in the rear differential, I have bad news for you.
The repair of a differential is often quite difficult and should be done by an expert. This is because of all the washers and other things inside the differential that have to be perfectly aligned.
Parts inside the rear differential are often quite expensive, and you can expect high repair costs if you add the labor costs to the work.
Since problems with the rear differential are quite rare and the cost of the parts inside the differential is very high, it is a much better choice to replace the differential. Of course, a brand new differential is very expensive and it is much cheaper to buy a used differential.
Depending on the car model, you can expect to get a used rear differential for $100-800 and labor costs of $100-500.
If you have any further questions, please let me know in the comments section below.