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Rear End Noise Diagnose and Fix a Differential in Your Car Truck or SUV

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Created on: 2019-04-22

How to diagnose a rear end differential.

Tools needed

  • Pry Bar

    Soft-Bristle Brush

    Dial Indicator

    Gear Marking Compound

    Marker / Writing Utensil

So right around 40 miles an hour, lightly accelerating, I can hear a howling noise that's coming from the back of the vehicle. When I let off the gas, the noise goes away. When I step on the gas, it comes back. I can actually feather the gas pedal and make the noise come back and forth. It's pretty bad.

What's up, guys? I'm Andy from 1A Auto. In this video, I'm going to give you some tips on how to diagnose a rear differential. If you need any parts for your vehicle, click the link in the description and head over to 1AAuto.com. All right when you're diagnosing the rear end noise that you have, if it's a noise that's constant all the time, what you can do is you can put the vehicle up on a lift and have someone driving. Be careful when you're doing this. You want to stay away from this area because this is going to spin real fast with the driveshaft and the yoke and stuff. But you can take a stethoscope and you can check right here in this area.

If it's a real loud in this area, you're going to have a problem with your pinion bearing. If it's real loud on the side, over here and over here on this side, it's probably your carrier bearings, and then also if you're only hearing it when you're accelerating versus decelerating or vice versa. It's probably your ring and pinion. Another thing you can check with is by using chassis ears.

You can actually attach chassis ears right here and right here and over here. What chassis ears are are basically little microphones that are attached to wires. Some of them are wireless and then you can drive the vehicle around and listen to where the sounds are and see which sound is closer to the actual noise you're looking for. Another possibility is the bearings over here. Those could be making noise.

It's not as common to have these bearings go bad. But it does happen. But generally, it's the carrier bearings or the ring and pinion bearings. I set up this dial indicator to check the backlash before I take this completely apart. This isn't normally what you would do. But my assumption with this rear end is it was set up wrong and that's why I'm getting a noise. So I just wanted to baseline it before I take it all apart, and see how the backlash is. What the backlash is, is basically the play between this gear and the pinion gear. There'll be a little slot and they're supposed to be. They're supposed to be about 8 to 12 thousandths of backlash.

Now what I do is I'm going to hold the pinion with one hand, and then I'm going to just rotate the ring gear back and forth and see how much backlash I have. And right there, I have almost 15 thousandths of backlash, which is way too much. Now they have different setups for a dial indicator you can use. They have some that have a magnet. That would be more ideal. This situation will work for us. It's the best I have available right now. So I want to check the pattern on this gear before I take it out. So I'm going to use some gear marking compound and an acid brush. Just mark this gear. We're going to mark both sides. What we're doing is we're going to try to see where the pinion is actually riding on the ring gear because it needs to be in a certain location. Otherwise, you're going to get a noise or it's going to wear funny.

So I'm going to take a pry bar, and I want to pry in here. And I'm just going to put a little tension on the ring gear so that it pushes down a little bit and spreads the gear marking compound. Once it goes that way, then I'm going to put the pry bar on the bottom and I'm going to spin the pinion in the other direction. As you can see on this side, that's where the pattern is pushing on the ring gear from the pinion.

The other side, it looks like it's pushing right there. So when we were checking our pattern in this ring and pinion when it was still in the vehicle, this one side, which happens to be the coast side, the pattern was actually pretty good. It looked just like this. It was right in the middle. It didn't look too deep. It didn't look too far forward or too far back. But when we were checking the drive side which is when we were accelerating, the pattern was way down here and way here.

So there wasn't a lot of contact touching the ring gear, which isn't good and that's why we were getting a noise. So it should be right there in the middle, a nice contact and we were getting it way on the outer edges and a thin line contact, which is causing our noise and what we found is it's probably due to lack of changing the fluid and there was a seal that was leaking and it was low. So when the pinion was riding up against here, it's actually worn down. The ring and pinion are worn. So it's not making good contact there.

We replaced the ring and pinion, all the bearings, and put in the correct shim. Okay, so we set this up again and put our gauge on and we'll just check in the backlash and we have about eight thousandths, which is awesome. That's exactly where we want to be. You don't want to be too high. You want to be over 12 thousandths and you don't want to be much under seven thousandths. So eight thousandths is awesome. So we're going to send it like that.

In case you don't understand what I'm talking about when I'm talking about backlash and this measurement right here, what it is is the ring gear and the pinion. There's an air gap between the two and if that air gap is too tight, then when all these components heat up, it's going to bind up and cause a lot of wear and then if the air gap is too loose, then you're going to get clunking while you're accelerating and decelerating. So that is why it's important to have this adjustment adjusted properly. So we have the backlash set up. So we're good there. So now we want to check the pattern.

So I'm going to take some gear marking compound and a small brush. Just mark this up. I'm going to mark it up on both sides of the ring gear. Okay, now we're going to check the pattern. I'm going to have a friend turn the pinion while I use the pry bar, and I'm going to put a little pressure on it. And what the pressure is doing is making it so the pattern's going to spread a little bit better. Otherwise, if you just do it freewheeling, then it's going to have as good of a pattern. All right, you can stop.

Now we're going to go the other direction. So now I'm going to pry from the top. All right, go ahead. First, we're going to look at this side. Now this area right here is where the pinion was contacting the ring gear. Now this is the driver side. So when you're accelerating and going forward, this is where it is pushing on the ring gear. Now ideally, I would have rather it been closer to the middle. But that actually looks pretty good where it is. It's a nice pattern. It's nice contact. It's oval.

It's not coming off the edge, which it looks really good and then if I looked at the coast side. There's a nice oval on this side as well and it's pretty close to where I want it to be. Ideal would have been closer to the middle. But that looks pretty good.

All right, so we're done. We finished our repair. We replaced the ring gear and we replaced the bearings while we were in there too and it's probably kind of hard to hear on the camera. But the rear differential is nice and quiet. So we actually fixed our problem and we're good to go.

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