How to Diagnose Rear Differential Noise

In Transmission by Magnus SellénLeave a Comment

The rear differential is extremely important when it comes to the proper overall functionality of your vehicle.

This component allows torque to be generated through the car’s crankshaft out to the wheels. Issues with the rear differential is quite rare, but if you are unlucky you might have a damaged differential

Here is an article of how to diagnose problems associated with the rear differential and how much it will cost to repair or replace it.

Diagnosing of a rear differential

A lot of people struggle with diagnosing problems associated with the rear differential and struggles to decide if the problem is actually a bad wheel bearing or a bad differential.

Even me, after a lot of years diagnosing these kinds of problems, can struggle with it.

Here is how I usually do when I’m diagnosing problems with the rear differential.

Lift up your car on jack stands

The first thing you should do is lift up your car on jack stands with help of a floor jack (or a car lift). Raise up both of the rear wheels of your car and make sure that your gearbox is put in Neutral.

1. Turn one wheel slowly

Check if the other wheel is spinning backwards of the direction you are turning the wheel – This can be different depending on which kind of differential your car has, but the most cars use an open differential and in this case, it should turn one wheel backwards when you are turning one wheel 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 you cars gearbox is in neutral, you should be able to turn the wheel freely. If both wheels are spinning when you are turning the other wheel – you might have a problem in the differential.

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3. Start the engine and put it in gear

If your car is equipped with an ABS/ESP system, you have to disable this first, normally with a button inside of the car. Let the car idle at a gear. Make sure that the jack stands are placed safely under your car. You do never want to go under your car without jack stands!

Keep your arms away from driveshafts, wheels and other rotating parts. Listen carefully if you can hear any noises from the differential. Usually, the differential should be very quite and if you hear a howling noise from it – it’s most likely damaged.

At the same time, you can listen for any noises out from the wheels. This might be to a bad wheel bearing rather than a bad rear differential.

4. Check the differential fluid

Pour out the differential fluid and check for any signs of metal pieces inside of it. You might find some small amount of metal pieces in older cars, which haven’t got a fluid replacement for many years – this is not abnormal.

If the fluid looks fine, you can fill it up again with the old fluid and if it’s dirty or black – replace it at the same time. Check with your manufacturer to find out which oil you should use in the differential.

Rear differential vs Wheel bearing noise

If you can’t find any noises or any metal pieces in the differential – it might actually be a bad wheel bearing instead of a bad rear differential. The process of diagnosing this can both be simple or advanced – depending on the problem.

Take your car for a ride

Drive your car up to around 80 km/h or 50 mph on an empty road. You might hear a howling noise at this point from the rear of the car.

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Turn the steering wheel slightly to the left and the right. If the howling noise changes frequency – you might have a bad wheel bearing. For example, if you are turning right and the sound gets higher it’s most likely the left wheel bearing thats the problem and vice versa.

This is because when you are turning the car, all weight is put on the opposite side and this may cause a lot more stress on the damaged wheel bearing which makes it louder.

If the noise isn’t changing frequency or level when you are steering the car at higher speeds your problem is most likely in your differential or your gearbox.

Let a passenger sit in the backseats and let them decide if the problem is coming from the front or behind of them to determinate if the issue is in the transmission or in the differential.

Prevent issues with the rear differential

There are actually not a lot of things you can do to prevent issues with the rear differential. It is a very compact piece which you cant do a lot of maintenance with. But there are two things you should know about rear differential maintenance.

  1. Replace the differential fluid at the right time. Check with the manufacturer or in you service documents when you shall replace the differential fluid. A lot of differential fluids should never be replaced if you ask the manufacturer – but it is never a bad thing to do anyway.
  2. Make sure your differential do not have any leaks. By checking around the differential cover and the axles for any leaks, you know that the differential level is good. A differential that is not leaking should never go low on fluid. Sometimes the differential fluid can leak out through the axles though, so you have to make sure that there is no fluid inside of the rear brakes. You can also check the differential level by the level-plug. Check-in your repair manual to find the level plug. Low differential fluid level can cause serious damages to your differential.
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Rear Differential Repair or Replacement Cost

If you checked the guide above and decided that the issue must be in the rear differential – I have some bad news for you.

Repairing a differential is often pretty difficult and it should be done by an expert. This is due to all of the shims and other stuffs inside of it that have to be in a perfect way.

Parts inside of the rear differential are often quite expensive and you can expect a high repair cost when adding the labour cost of the work.

Because issues with the rear differential is pretty rare and the cost of the parts inside of it, a much better choice is to replace the differential. Of course, a brand new differential is very expensive and it is a much more cost-efficiency to purchase a used differential.

Depending on the car model you can expect to get a used rear differential for $100-800 and a labour cost of $100-500.

If you have any more questions, let me know in the comment section down below.

Hello I'm Magnus, the owner and the writer of this website. I have been working with cars since I was 16 and I'm specialized with in-depth Automotive diagnostics. Also been driving drifting for the last 6 years. I'm here to give you answers to all your automotive questions and I hope that you enjoy our content.

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