Rear Axle / Differential / Pinion Bearing?

Congrats on getting started, but this is one repair you'll want to steer clear of. I'd be happy to post the instructions for replacing the bearing, but setting up the backlash and pinion depth is an extremely tedious job that requires precision and patience to prevent gear noise and premature gear wear. The people at most independent shops won't attempt this job, and dealer's service departments typically have only one or two people qualified to do it. I replaced the bearings on one rear axle while at the dealership. It took over a day to get it right, and I had to borrow special tools from a couple of the other mechanics.

A better suggestion is to find a low-mileage entire axle assembly from a salvage yard. Failures aren't common, so they don't get a lot of chances to sell a complete axle. That means you can often finagle a lower price. Also look for one of the "pick-your-own-parts" yards. Do a search for "Pull-A-Part", for example, and see if they have a yard new you. I've been to 16 of their yards. Prices are very low and employees and other customers have always been very friendly. All of their yards are very clean and well-organized too. You toss your toolbox in one of their wheelbarrows and you can spend all day there if you want to. Similar yards are popping up all over, but I'm not familiar with their names or locations.

Here's Part 1 of the overhaul instructions. From the little of it I read, it appears they haven't even reached the pinion gear and bearings yet, but this will give you an idea of what is involved.

Here's Part 2 of the procedure.

Better to be discouraged than frustrated and disappointed. Many years ago my '72 Dodge Dart developed gear noise in the rear axle. Chrysler has always been well-known for good parts interchangeability. That car used the smallest axle made at that time. I found the third largest of the five they were using, and it fit right in. Driveshaft, brakes, parking brake cables, and wheel spacing were all the same. Just needed larger U-bolts. In your case you have to be sure to find an axle with the same gear ratio because of the 4wd. For my car, I went from a 2.72 rear gear to the common 3.23. Funny thing is acceleration improved hugely, while the gas mileage stayed exactly the same. The engine was running faster, but at much lighter throttle. Made the car a lot more fun to drive.

Please keep me informed on your progress and how you handle this.

This is an easy job at any salvage yard. They have very large books called "Hollander Guides" to find compatible parts. You look up your model and year, then go to the "Drivetrain" section where all the parts or assemblies are listed. Each part will have a code number. Those used to be three-digit codes, but I think they're longer now. Go to the back section of the book and find that code number. There it will list every model that might have used that part. You still have to look for things that could vary, like wheel diameter or headliner color, etc. In your case it will tell you which vehicles and years could have used the same axle assembly, but you have to verify you found one with the right gear ratio.

First look in the glovebox. Trucks used to commonly have a sticker listing all of the options on that vehicle. The gear ratio was listed there, but possibly only if it was ordered with an optional, or non-standard ratio.

Next, there is usually a metal tag under one of the bolt heads for the differential cover. The ratio is stamped on that.

There is also a sticker on the driver's door opening, but I don't know if they put the gear ratio on that.

The last place to look was used by Chrysler since at least the 1960s. That was a metal plate on the driver's side inner fender. It listed paint codes, interior trim codes, and things like that. Engine size was two letters or digits that were also found in the vehicle ID number. As I recall, the gear ratio was listed as the actual number, not as an options code. I've been told other manufacturers used a similar plate or method to list special information.

If none of these things pan out, you'll have to remove the front or rear differential cover, then the gear ratio is stamped on the outer edge of the ring gear.

A final method that might work but with less accuracy is to rotate the driveshaft by hand, and count how many times the wheel turns. This is a little tricky because both wheels have to rotate the exact same number of revolutions, the same as if you were driving on a straight road. As an alternative, you can block one wheel, then the other one on that axle will rotate twice as many times. To get better accuracy, the way I would do this is to put a chalk mark on the driveshaft to make counting the revolutions easier. Also put a mark on the tire, or have a helper count the revolutions by watching the valve stem.

If you have true four-wheel-drive, the front driveshaft and wheels should not be turning. If you have all-wheel-drive, the front will usually want to turn too, so you'll have to raise at least one front tire off the ground. With automatic transmissions in neutral, the driveshaft usually turns fairly easy in the forward direction. Trying to turn it in reverse forces additional components in the transmission to rotate, making turning it that way much harder.

One revolution of the tire can make it difficult to know exactly how many fractions of a revolution you ended up with. Instead, count the number of driveshaft revolutions to make one wheel rotate ten times, while the other wheel is blocked. For Chrysler's common 3.23 gear ratio, you'd expect to turn the driveshaft 16.15 revolutions, (roughly 16 1/4). That means 1.615 driveshaft revolutions to make the wheel rotate once. Had the other wheel been free to turn at exactly the same rate, the driveshaft would have had to rotate twice as much, or 3.23 revolutions to make both wheels rotate once.

If the math confuses you, just tell me how many times you rotated the driveshaft to make one wheel rotate ten times, and I'll do the calculating for you.

I checked a couple of sources and no one lists the gear ratio(s), so there might only be one. If there were other options available, that should be mentioned in the Hollander Guides.