Does your auto make a grinding or howling noise when driving? Does it whine when you speed up or slow down? If your car clunks, knocks, grinds, howls, or whines, you need to know how to fix a noisy differential.
How to fix a noisy differential: Replacing the differential fluid may stop the sound, or replacing a pinion or side seal may solve the problem. However, once the noise gets bad, rebuilding or replacing the differential may be the best way to fix the noise.
In this article, we’ll focus on unusual noises from the front or rear diffs, what could cause the sound, and what you can do to repair it. We explain what a differential is and provide a simple description – we don’t explain all differential types. We also look at what it can cost to repair or replace a differential. By the end of the article, you should have a better understanding of what different differential noises are warning you about, and how to stop the sound.
For information on quieting other automotive noise, please see our articles:
How to Soundproof a Noisy Water Pump
How to Quiet Noisy Strut Mounts
How to Fix Noisy Lifters
What is a Differential on a Car and How It Works
The most common differentials are front-wheel drive and rear-wheel drive differentials. They use gears to change the direction of torque or power from the engine equally between the drive wheels. It is located on the rear axle of rear-wheel-drive vehicles, where the driveshaft meets the axle. The bulge in the axle houses the differential.
On front-wheel drive vehicles, the differential is located at the end of the transverse-mounted engine. On a part-time 4-wheel drive, the front and rear differentials lock together when engaged.
This delivers the same torque to both sets of axles, which is why steering at slow speeds is more difficult. All-wheel drive vehicles have a third differential located between the front and rear axles to allow the steering axle to turn at different speeds for easier cornering.
Most modern automobiles have a split or co-axial differential that allows the left and right wheels to rotate at different speeds when cornering or on uneven surfaces. If the axles weren’t split, both wheels would spin at the same rate, which is problematic when cornering – damaging the shaft, stripping gears, or causing the vehicle to spin out of control.
On straight, smooth roads, they operate at the same speed. ‘Positraction’ or limited-slip differentials (LSD) are co-axial axles that allow some torque to be transferred from one axle to the other if one tire is spinning on ice, snow, wet pavement, or mud.
The differential is made up of different gears that split the rotation of the engine power to the left and right wheel assemblies. They are commonly known as planet gears and sun gears. The planet gears spin around or are driven by the sun gear.
An input pinion gear (flat-end cone-shaped) is turned by the pinion shaft at the end of the drive shaft. It meshes with a bevel or ring gear. It is an open-bottomed pie-plate looking gear with the left or right axle going through the open bottom. The differential end of each split axle is a bevel or side gear, also known as a sun gear.
They are driven by two bevel or pinion gears – also known as spider gears. The spider gears are connected to the ring gear and are off-set 180° from each other. They mesh with the side gears at 90° to drive each axle, transferring drive rotation but preventing flexing of the co-axial axle.
Simplified, the engine turns the shaft, which turns the input pinion gear. The pinion gear turns the ring gear. The two pinion or spider gears are attached to the ring gear and rotate with it between the beveled side gears at the end of each co-axial axle, rotating them and delivering drive power to the wheels.
What Are the Causes of Differential Noise
All vehicles make noises when they drive, and almost all have at least one differential. Differentials are finely tuned mechanisms that seldom need repair; they can last for hundreds of thousands of miles without fail. However, if you experience clunking, grinding, whining, or another bad differential sound when accelerating, decelerating, or cornering, it could indicate that something isn’t right in the differential.
Differentials fail if they are overloaded when towing, or don’t have enough differential fluid to lubricate and dissipate heat due to a leak. Immersing a hot differential as you drive through a deep puddle, creek, or unload a boat, can cause the housing to crack or a seal to leak. Water in the differential can play havoc with the lubricant and damage gears and bearings.
Here are some noises you may hear when your differential needs service, and what could cause the sounds. Remember, these are sounds new to your automobile, not the regular everyday racket:
A worn pinion bearing noise indicates excessive clearance with the ring gear, generating a humming or whine.
A clicking noise when slowing down from 20 mph to a stop may indicate an issue with the side-gears, or the carrier case bores may be worn. Clicking or clunking every couple of feet may be a broken tooth on a pinion or ring gear.
If you hear a squeaking or grinding noise when driving, it’s likely a universal joint that’s damaged or worn.
Hearing a whirring noise around 10 mph when accelerating or slowing down is likely due to worn or loose pinion bearings.
Worn axle shaft splines or chipped gear teeth can lead to a knocking or clicking rear differential noise from the differential.
A low-pitched rumble at speeds greater than 20 mph may be a carrier bearing noise warning it’s wearing out. A rumbling or clicking from a worn wheel bearing will sound worse when performing hard turns, making it easier to tell apart.
A clunking or banging when cornering, reversing, or quickly slowing down from highway speeds may be from worn spider gears or clutches, or lack of or incorrect lubrication. Hearing the noise when accelerating may be due to worn or loose axle or yoke splines, spider or U-joint wear, or differential backlash noise. The clunk, when starting from a stop, could be caused by worn out slip yoke splines.
When cornering you hear a banging, popping, or crunching sound, it could be from worn or damaged spider gears. Pinion gears with damaged or broken teeth can cause a banging or clicking noise every 2 or 3 feet when increasing or decreasing speeds. If the rear end noise is every 8 feet or so, then the ring gear has damaged or broken teeth.
Whining Noise on Acceleration/Deceleration
A whining or howling differential noise on accelerating or decelerating may be caused by a loose gear inside the differential.
A worn U-joint can cause vibration through the vehicle, as can a driveshaft being out of balance. If the vibration is worse at a particular speed, or when slowing down, then it is the angle of the pinion gear – it is misaligned.
Noise When Turning
A noise that maintains the same pitch or intensity when steering at any speed often indicates a problem with the meshing of gears within the differential. If the noise increases pitch or intensity when cornering, it usually indicates a wheel bearing is failing.
A howl when slowing down but not braking is a bad pinion bearing symptom. The same noise when accelerating could be due to overloading or low lubricant levels. If accelerating and the howl is accompanied by a rumble or whir, it could be from a worn gear set or worn pinion or ring gear or bearings.
How to Diagnose Differential Noise
Diagnosing a front or rear differential noise and determining it isn’t from a failing wheel bearing isn’t always easy. They produce similar sounds and even affect the drive and handling in similar ways. Considering both affect the handling and safety of your ride, it’s best to determine what needs repair and fix it.
Take the car drive on a fairly empty road. You want to be going around 50 mph, so listen for the howl of ring and pinion noise on acceleration. While cruising at speed, listen to the howling noise. Turn the wheel slightly left, and right, you don’t want to lose control or veer into another lane, so watch the road too.
You want to listen to the noise. If it gets louder when steering left, it’s the left wheel bearing, louder to the right is the right wheel bearing. However, if the noise stays the same, it’s rear or front differential noise.
If you suspect it is a failing differential based on the sound or handling, put the vehicle up on jack stands or a hoist. You want the drive wheels off the ground, and blocks behind non-drive tires if on the ground. With the engine off, shift the car into neutral, and rotate one wheel forward or back.
Most automobiles have an open differential, so the wheel on the other side of the vehicle should rotate the opposite direction. If both wheels rotate the same direction, it may not be an open diff, or you’ve identified there is a problem in the differential.
Have a helper hold one wheel so it can’t rotate, or use a block to prevent one drive wheel from spinning. If the vehicle is in neutral, you should be able to spin one drive wheel while the other is held. If you can’t, there’s a problem.
With the car still on jack stands and both drive wheels able to rotate freely, start the engine. Disable the ABS/ESP system – there’s usually a button. Shift into a forward drive gear and let the engine idle. Stay away from moving parts, and listen to the differential – it should be quiet. If it howls, grinds, clunks, bangs, whirs, clicks, vibrates or makes other unusual sounds, it’s damaged.
If you don’t hear any noise from the differential, but the noise is coming from one of the drive wheels, it’s probably a wheel bearing and not the differential.
How to Fix a Noisy Differential
Fixing a noisy differential is possible to do yourself, especially if you’re mechanically inclined, have the tools, and time. Once your differential begins making noise, you should expect repairs on the horizon. The clearance for most moving components in the differential is measured in thousandths of an inch, so there isn’t much space for error or broken gear teeth without creating more damage.
The longer you wait, the more costly the repairs may be. Repairing the differential assembly means removing the cover on the back of the differential. It’s a messy job and should be done on a hoist or jack stands.
Replacing the differential fluid may be an easy solution. Review the owner’s manual to determine when the differential fluid should be changed. If nothing is leaking, but the vehicle has between 30,000 and 60,000 miles for front differentials or 30,000 to 50,000 for rear ones, the fluid should be changed since the oil will break down over time.
Drain the fluid. If you notice small pieces or filings of metal in the oil, you should remove the cover plate and clean and inspect the inside as much as possible. Replace the seal and differential oil.
Check to see if there are any leaks at the differential. If there are signs of grayish, black, or light brown fluid leaking on the garage floor or driveway or the diff housing, a seal is going or gone and should be replaced, as should the fluid inside the housing.
The gears inside the differential are immersed in oil to lubricate and help dissipate heat. Replacing the rear differential gasket is straightforward once the oil is drained. Removing and replacing the pinion seal or side seals are more complex.
- A rear differential pinion seal necessitates the removal of the yoke where the driveshaft and diff meet. Remove the seal around the yoke and replace it without damaging the new one. Reassemble and refill the differential oil.
- The side seals prevent the oil from seeping into the brakes. Removing them requires first removing the axle shaft(s), and then removing and replacing the leaky seal(s), before carefully reassembling everything.
Once you’ve identified what needs to be replaced inside the differential, then the part(s) need to be ordered, including a new seal or seals, and replacement fluid. Once the gears are exposed, it is easier to note what actually needs to be repaired and if your diagnosis was accurate.
- Replacing pitted or damaged bearings may fix the noise. It requires dismantling the differential and possible replacement of side or pinion seals. Most shops list it as a 3 to 5-hour repair.
- Chipped or worn teeth on any gear require the replacement of that gear, and potentially other gears or bearings that have been damaged by broken pieces. It could take a trained mechanic 6 to 8 hours to do the repairs if the replacement parts are on hand.
If you wait too long to repair the differential and the inside looks like a grenade has exploded inside with broken metal teeth and pieces resembling shrapnel, it may be less expensive to replace the differential.
Can You Drive With a Bad Differential Sound?
The differential is a crucial component of a vehicle’s drive system. If it is making unusual noises, then it is warning you that something isn’t right. The sooner the noise from a differential is fixed, the less damage that may be caused, and the safer your ride will be.
Driving with a bad front differential or rear diff at slow speeds for a short distance is possible – home or the mechanics – but travel distance and speed should be limited. Driving along a freeway and having your drive wheels lose power, seize, or break away, isn’t the safest choice.
Differential Repair Costs
Repairing a differential is a dirty and messy task. Removing and replacing any gears inside the diff isn’t easy, or cheap. There are shims, bearings, and moving gears that fit with the precision of a thousandth of an inch. Everything must fit perfectly, or it will soon need repairing again.
Doing it yourself will save on the shop charges. However, if you have to buy specialized tools, that savings may be minimal. Aftermarket parts may save 30% to 40% over OEM parts, and reduce costs. If you take it to a reputable mechanic, expect to pay between $800 and $2000 or more for a repair.
Shop fees range from $85 to $165 in my area – an 8-hour repair can add up quickly! It may be cheaper to replace the differential.
Differential Replacement Cost
Replacing or rebuilding a differential are two other options for fixing differential noise, and both can take several days to accomplish. If a rebuild or used diff is a possibility, it could save up to 50% over a new differential. It is not an easy DIY task and may be better left to a licensed mechanic.
A new differential will run an easy $1500 to $4000 installed, while a rebuild (used) will set you back between $700 and $2000 installed. However, much depends on the make, model, and year of your vehicle, plus whether it is front or rear-wheel drive. A bonus of having it replaced professionally is that they usually include a warranty.
The differential is a vital part of a vehicle’s drive system. It can quietly carry out its purpose for thousands of miles, but when it starts making noise, maintenance, and repair are necessary. Following the manufacturer’s instructions and replacing the differential fluid when recommended may prevent expensive repairs. If you’re hearing differential noises, you may already be looking at an expensive repair or replacement.
Hopefully, you have a better understanding of what differential does, how to diagnose different noises, and how to stop differential noise. Your suggestions and comments are appreciated. If you found the article interesting, please pass it on to others who may be interested.