Where Is The Pinion Seal and Why Is It Important

Hi, I'm Mike from 1A Auto. We've been selling auto parts for over 30 years.

Hey, everyone. It's Sue at 1A Auto, and today I'm going to show you a quick little lesson about rear differentials. You ever been to a shop, a dealer and they tell you their rear pinion seal is leaking? Well I want to show you what a real pinion seal is and give a quick review on how a rear differential works. So if you come up to the front here, this is your pinion seal for the rear. Rear pinion seal right here. You get your drive shaft, which is U-joints. Goes into a yoke, which goes into the pinion part of the differential. And that's the seal.

And you can see how it's all wet here, that means that that pinion seal is leaking. Some people might say it's not a big deal--don't worry about it. Well, it is a big deal because if the fluid is getting up here and running out, this pinion bearing gear is running dry and that can cause a howl, and then you can talk about a whole rear end differential rebuild or replacement. Three-grand. It's not something you want to do, right? So spend the $120 to $180, estimate, roughly, on a pinion seal.

So when you move back here to the differential, this is what the inside of a differential looks like. It's pretty basic. Almost looks primitive, doesn't it? Your front gear there that you can't see if you look through here in that gear that's right there, that's attached to the driveshaft, and that's called the pinion gear. That's why they would call that a pinion seal. It's in front of it. This is your ring gear. Then you have spider gears, and these are your differential gears. So when the drive-train spins, the ratio up there is smaller than the ring gear and the ring gear turns at a slower speed, and that turns at a faster speed.

When you're going straight ahead, all the gears, the differential gears and the ring gear, everything's going forward. Each gear is a different size. Well your ring gear's a different size than your pinion gear for a reason, so you can turn a corner without a shake or a shutter. So when you turn a corner, if you take a left, the outside wheel here is going to turn more ratio than the inside wheel. You don't feel it happening, but inside here it's doing its job. This gear-ring gear turns slower as the outside axle turns faster.

So to recap--the differential is nothing to take lightly, even though it's very heavy. So you want to keep the fluid clean. Do the maintenance. If you have leaks, if the differential cover gasket's leaking, or if you have axle seal leaks, like we had an axle seal, you can see leakage on the outside here by the tube where it meets the backing point. Do the maintenance. Get it done. It looks primitive, but it's very intricate and without it, believe it or not, the car doesn't go forward or reverse.

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