You may recall a mechanic’s warning about “rear differential problems.” You may even just suspect an issue. If this is it, is it safe to keep driving with a bad rear differential?
Technically you can drive with a bad rear differential. However, this is highly discouraged as it could aggravate its damage and compromise your safety. Regardless, driving a vehicle with a bad differential is challenging, given the intense vibrations and unpredictable steering behavior. Keeping the car pointed in a straight line is a constant battle.
Before you decide for yourself whether you should drive with a broken rear diff. First you should understand what it does and why it fails. I cover all this in more detail in this article.
What is the Rear Differential? How Does it Function?
The rear differential is part of a car’s transmission on a four or rear-wheel drive vehicle. In simple terms, it is a gear arrangement/box located between the rear wheels of your vehicle. Its job is to take the power from the engine and distribute it to the wheels, so your car can move forward or backward.
When you drive in a straight line, both wheels are required to spin at the same speed. The rear differential gets its power from the engine; power is sent through the transmission into the diff, split into two equal parts, and sent to both rear wheels.
However, when you turn your car or drive over bumps, the wheels need to spin at different speeds even at the rear. This is because the wheel on the outside or the one going over the bump has to travel further. To keep the car in control and get around the corner the wheel on the inside will need a different amount of power to the one on the outside. A rear differential is smart enough to control this, so it will send slightly more power to the outside wheel and less to the inside wheel.
If a car didn’t have a differential both wheels would received equal power and if were to drive fast around a corner wheels would break traction because of the unnecessary extra power.
3 Majors Symptoms of a Bad Rear Differential
Consider what would happen if the electrical panel in your house, which distributes power to your appliances, started to malfunction. The lights on one side of the house might work but not the other. Similarly, when a car’s rear differential begins to falter, noticeable symptoms begin to emerge.
At first, these signs might be subtle and easy to overlook, but as it gets worse, which it will! The vehicle’s performance significantly declines. Three key indicators of a faulty rear differential include:
One of the most noticeable signs of a bad rear differential is abnormal noise from the rear. This can vary based on the level of damage, the type of car, and the surface you are driving on. Some noises to look out for include a humming sound that increases with speed, a rumbling noise when turning, or even a loud metal-on-metal knocking sound.
These noises are actually from the gearing system within the differential. For instance, a damaged bearing or backlash within the ring and pinion produces clunking sounds, especially when you put your car in drive.
The noises may be barely noticeable at first and progressively worsen as you drive.
The noises are accompanied mainly by vibrations. Again, that’s because of the gear ring in the differential. When the gear is worn or damaged, it may not mesh together correctly. Improper gear meshing can result in a vibration or jerking felt throughout the vehicle.
Initially, these vibrations might be slight and occur only at certain speeds or when making specific turns. However, these vibrations may become more consistent and intense as the differential deteriorates.
Note that vibrations can also be caused when there’s a problem with the tires or suspension. So, check the issue before you conclude the diff needs fixing.
If the differential is not working correctly, it can cause handling problems. This type of problem is more commonly associated with a failed front differential. But, it can also cause the car to snatch at the back when the rear diff has failed. This is because the differential helps balance the speed of the wheels.
A damaged differential fails to provide the right amount of torque to the wheels, leading to the vehicle pulling to one side or the other or an unusual feeling in the steering wheel, especially during turns. This shaking or wobbling sensation is abnormal and should be addressed immediately; it can cause the car to pull violently to one side when accelerating or turning randomly.
4 Reasons a Rear Differential Goes Bad
Like other mechanical parts, differential also fails due to specific reasons. Knowing those reasons will help you prevent this malfunction from happening. Here are the key reasons:
Lack of Differential Oil/Wrong Oil
The differential oil, or gear oil, critically lubricates the gears and bearings, reducing friction and helping disperse heat.
If there’s not enough oil or the wrong type of oil is used, the components inside the differential can wear out faster due to increased friction. Over time, this can cause the differential to fail.
Lots of off-road driving can be tough on differentials. The uneven terrain can lead to more intense variations in wheel speed, putting extra stress on the differential.
If the off road driving involves lots of dry dusty roads, this can cause the driveshaft seals to wear, which could lead to a fluid leak.
Regular maintenance is vital to keeping a differential in good working order. This includes periodic inspections for leaks and damage and frequent oil changes. These tasks are necessary to avoid problems going unnoticed and causing the oil to degrade, resulting in differential failure over time.
Physical damage to the differential from accidents or impacts can cause immediate failure or weaken the components, leading to failure. Even minor incidents, such as debris hitting the diff casing, are enough. Any damage, no matter how serious, can cause a misalignment issue, damage seals or the casing, leading to oil leaks or other problems.
Why is it Unsafe to Drive with a Bad Rear Differential?
Technically, driving is possible if your car shows signs of a bad differential. But it’s not advisable since it would further deteriorate the differential internals and may cause the vehicle to come to a stop without warning. There are also other factors to consider when driving with a faulty rear diff:
It Causes Excessive Tire Wear
Tires with diminished tread are less effective at maintaining traction on the road. Which results in increased stopping distances and poor maneuverability, especially in conditions where the road is wet or slippery
Car May Face Difficulty in Acceleration
A failing differential can limit the adequate distribution of power to the wheels. This could mean your vehicle has difficulty accelerating as one rear wheel gets all the power the other gets nothing. This can be hazardous in situations that require quick acceleration, like overtaking another vehicle.
Poor Traction is a Safety Concern
The differential’s job is to allow the wheels to spin at different speeds to maintain traction. If it malfunctions, it can cause the wheels to spin when they shouldn’t, reducing the vehicle’s overall traction. Consequently, the car becomes more difficult to handle, particularly in adverse weather or off-road conditions. Drift cars typically weld their rear differential to break traction with minimal effort. If the diff locks up, you will have the same scenario.
The Car Pulls to One Side
The differential has a role in balancing the vehicle, particularly when cornering. When its differential gear fails to mesh correctly, the imbalance causes your car to pull one side, shake, or feel ‘loose’ while driving. This causes instability, increasing the risk of accidents when moving at speeds or during sharp turns.
This article clearly shows that you can drive with a bad differential. But the real question is it safe? No, it’s not. Driving with a faulty differential can pose significant risks, from excessive tire wear and decreased vehicle power to poor traction and instability, all of which could lead to dangerous situations on the road.
While ignoring the signs and pushing on might seem tempting, the potential cost to your safety and wallet should put you off.