How to Check Backlash and Pattern on Rear Differential 2009-14 Ford F150

What's up, guys? I'm Andy from 1A Auto. In this video I'm going to show you how to check the pattern and the backlash on this rear differential. If you need parts for your vehicle, click the link in the description and head over to 1aauto.com.

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 setup wrong and that's why I'm getting a noise. 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 slop and they're supposed to be. They're supposed to be about 8,000 to 12,000 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, rotate the ring, the ring gear back and forth and see how much backlash I have. Right there I have almost 15,000s of a 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. I want to check the pattern on this gear before I take it out. I'm going to use some gear marking compound and an acid brush. Just mark this gear. We're going to mark both sides. 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.

I'm going to take a pry bar, and I want to pry in here. I'm just going to put a little tension on the ring gear so that it smashes, it pushes down a little bit and spreads the gear marking compound so that we can see the pattern. I'm going to go in one direction first while I spin the pinion. Once it goes that way, then I'm going to put the pry bar on the bottom and then 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, looks like it's pushing right there.

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, looked just like this. It was right in the middle. It didn't look too deep, 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, it was way down here and way here. 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 like right there in the middle, a nice contact, and we were getting it way on the outer edges, and a thin line of contact, which is causing our noise.

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 this was 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.

Okay, so we set this up again and put our gauge on, and we're just checking the backlash. And we have about 8,000s which is awesome. That's exactly where we want to be. You don't want to be too high. You don't want to be over 12,000s and you don't want to be much under 7,000s, so 8000s is awesome. 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, 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. Then if the air gap is too loose, then you're going to get clunking while you're accelerating and decelerating. That is why it's important to have this adjustment adjusted properly.

We have the backlash set up, so we're good there. Now we want to check the pattern. I'm going to take some gear marking compound in a small brush, just mark this up, and then mark it up on both sides of the ring here.

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. What the pressure is doing is making it so the pattern's going to spread a little bit better. Otherwise, if you do it, you just do it freewheeling, then it's not going to have as good of a pattern. All right, you can stop. Now we're going to go the other direction and now I'm going to pry it 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 drive side. So when you're accelerating 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. Then if I looked at the coast side, it is 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.

Thanks for watching. If you want the parts to do it yourself, check out 1aauto.com, the place for DIY auto repair.