If you hear rear end noise including grinding, clunking, or rattling coming from your vehicle, you may have a bad differential. This is a common problem that car and truck owners encounter, especially in four wheel or rear wheel drive vehicles.
The rear differential helps to split the power sent from the engine two ways. It sends equal amounts of torque to the right and left wheels.
When you’re trying to go around a corner, for example, the wheel on the outer side of the turning arc must rotate faster than that on the inside. The differential is responsible for ensuring there’s a power balance since the wheels do not move at the same speed. This helps to provide traction and overcome resistance.
When you hear strange noises coming from the differential when accelerating at a certain speed, it’s important to have it thoroughly investigated.
Watch the video below or read our step by step guide in this post. We will take a look at some of the things you should look out for, how to diagnose a noisy rear differential, and how to fix the problem.
Symptoms of a bad differential
A standard differential is made up the right axle shaft, left axle shaft, a ring gear, pinion gear, side gears, and spider gears. When any of these parts are worn out or not properly lubricated, you may hear sounds coming from the rear end of your car.
Some of the sounds that you should look out for include:
- A howling noise when you accelerate – May be caused by a worn pinion gear, worn ring gear, or an improper fitment.
- A whirring noise when decelerating – May be caused by loose or bad bearings in the pinion gear or ring gear.
- Noise when cornering – May be caused by broken spider gears. These are also referred to as cornering gears.
How to diagnose rear end noise
Tools you’ll need:
1. Car lift
2. Car diagnostic stethoscope
3. Chassis ears (optional)
Steps to diagnose rear end differential problems
Step 1: Suspend the vehicle on a car lift.
Step 2: If you hear constant noise when you drive, have someone run the car while it’s suspended. Remember to stay away from the driveshaft and yoke. These spin very fast and can cause injury.
Step 3: Use your stethoscope to check the areas shown above.
If you hear a loud sound coming from part (1), you may have a problem with your pinion ring. If the noise is coming from the parts numbered (2), you may have a problem with your carrier bearings. If you only hear noise when accelerating or decelerating, you may have bad ring and pinion gears
Step 4: You can use chassis ears in place of a car diagnostic stethoscope to check for noise in your differential. Chassis ears are small microphones that you can attach to different parts of a bad differential to check for noise. They help you to spot exactly where the sound is coming from.
How to fix a rear end differential problem
Once you’ve identified where the noise is coming from, you’ll be better placed to fix the problem. In our case, the vehicle produced a howling sound every time the driver stepped on the gas. The sound would then disappear once he let his foot off.
In such a case, the cause of the noise may be piston and ring gears that are worn out or not properly fitted. The steps outlined below will help to fix the problem. You can also watch the video above.
Tools you’ll need:
1. ½ inch Socket and ratchet
2. Drain bucket
3. Dial indicator
4. Gear marking compound
5. Acid brush
6. Pry bar
12 Steps to fix rear differential that’s making noise
Step 1: Use the ½ inch socket and ratchet to remove the bolts securing the metal plate that covers the gear assembly. Have a drain bucket/pan placed right below to collect the differential fluid.
If the plate is stuck, use a flathead screwdriver to pry it off once the bolts are out.
Step 2: Set up your dial indicator to check for bad backlash between the ring and pinion gears. Checking for bad backlash helps to determine the amount of air gap present when the movement of mating gear teeth is reversed or when contact between the teeth is reestablished.
The presence of backlash is not entirely a bad thing. The right air gap helps gears to mate without binding and provides space for lubricants.
An air gap that’s too tight causes the gears to bind up when temperatures are high. An air gap too wide causes clunking when accelerating. Here, we are checking for backlash beyond the required amount. That is, anything above eight thousandths or twelve thousandths of backlash.
Step 3: Once you set up the dial indicator as shown in step 2, move the ring gear slightly back and forth to see how much backlash you have. In our case, the backlash was about fifteen thousandths. This is too much.
Step 4: Once you’ve determined the backlash, it’s time to check the pattern of the ring gear. Start by marking the teeth of the ring gear using an acid brush and gear marking compound. Remember to mark both sides of the gear teeth as shown above. This helps to indicate where the pinion gear is riding on the ring gear. If the pinion gear does not get into contact with the ring gear at the right location, this can cause noise.
Step 5: Once you’ve marked a several teeth, insert the pry bar at the spacing on top the ring gear. This helps to create tension and push on the gears so that they get into contact well. It also ensures the pattern that comes out spreads out effectively.
Step 6: While holding the pry bar with one arm, use your other arm to rotate the pinion from the back. You can start with the clockwise direction. Continue rotating the pinion until the part on the ring gear that’s marked with the compound just appears at the bottom.
Step 7: Remove the pry bar and stick it in the space just below the ring gear. Rotate the pinion in the opposite direction as you push on the pry bar to create tension.
Step 8: Once you’ve made a complete rotation, check the part of the ring gear where you had marked. Notice where the gear marking compound has been scraped off due to contact with the pinion gear.
On our vehicle, the coast side had a pattern in which the compound was scraped off almost in the middle forming a perfect oval shape.
The drive side, however, which shows contact when the vehicle is accelerating, had the compound scraped off on the lower side.
It also formed incomplete lines that indicated there was little contact between the ring gear and pinion gear. The inability of the gears to mate effectively explains the noise we heard every time the driver stepped on the gas pedal.
We found out that this was caused by not changing the differential fluid as required. There was a seal that was also leaking leading to low fluid. The result was worn out pinion and ring gears that didn’t mate properly.
Step 9: If you have worn gears, remove and replace the ring and pinion, all the bearings, and put in the correct shim. Shimming ensures there’s adequate tooth contact between the gears so that they do not rub on themselves.
Step 10: Install your ring and pinion gears and test the backlash using the dial indicator. In our case, the gauge read eight thousandths of backlash which is exactly what it should be. Ensure that you have nothing below seven thousandths or above twelve thousandths.
Step 11. If your backlash is okay, check the pattern of the gears using the same method described in steps 4-8. Apply some gear marking compound and check both the coast side and drive sides.
The pattern should have an almost perfect oval shape that’s at the center or close to the center. As shown above, the patterns came out perfect the second time after replacing the pinion gear, ring gear, and bearings.
Step 12: Take your vehicle for a test drive. Pay attention to your rear differential and listen for the same sound you had heard prior to working on your car. In our case, the rear differential was nice and quiet after replacing everything. It no longer made noise when accelerating.
How to take care of your differential to avoid rear end noise
Like most parts of your vehicle, it’s necessary to carry out regular maintenance on your differential. This starts with ensuring there’s enough differential fluid, which is also known as gear oil. It helps to protect it from wear and ensures it performs smoothly and safely.
The differential fluid on our vehicle was little due to a leak. This caused unnecessary wear on the pinion and ring gears. Ideally, you should have your differential fluid changed after every 30,000 miles. If you need new components, visit 1aauto.com for high-quality differential parts.