XJ Rear axle swap

[89 MJ]

There were three main rear axles found in the Jeep XJ, all of which should be fairly easy to swap into our Eagles. The three options are as follows:
AMC/Dana35
Chrysler 8.25 (available in both 27 and 29 spline axle shafts)
Dana 44
There are four gear ratios found in these rear axles that would be fairly available. They are as follows, along with the engine/trans combo they came with:
3.08: 4.0, manual trans
3.54: 4.0, automatic trans and 4cyl, 4 speed
3.73: Some early (1984-1986) XJs had these. Not sure on engine/transmission combos
4.10: 4cyl, 5 speed

Note: a Jeep MJ Comanche has the same width rear axle, but the perch width is different and they are spring under axle, not spring over like XJs and our Eagles are. Comanches did also have an AMC20 rear axle available in the 1986 model year only.

I had previously read that the XJ axle swap is bolt in, with the exception of the shock mounts. This is both true and not true. The axle itself is a bolt in swap, other than needing to move the shock mounts, but there are some things to be aware of.
1. The pinion snout on a D44 or Chrysler 8.25 is 1" longer than that of an AMC/D35, so the driveshaft will need to be shortened. I was able to just barely get away with not shortening the shaft as my car has roughly a 3" lift in the rear.
2. The diameter of the axle tube for a D44 or Chrysler 8.25 is larger than that of the stock rear axle. You will need the U-bolt plates out of your donor vehicle for this swap.
3. The brake line t fitting is on the other side of the rear end. On an XJ, the t for the lines/hose is roughly in the middle on the left side of the axle. The t for an Eagle is near the right side axle perch.
4. I read that the pinion angle is correct using XJ perches. I do not think that it is, the pinion is pointed towards the floor a little bit more than I would like. That said, my car has a lift, so that may not be the case with a stock height Eagle. I will also say, even with this pinion angle not being 100% correct, it is not far enough off to the point that I worry about the pinion bearing not getting enough oil. I've also had my car up to 80 since the swap with no driveline vibration. I didn't dare push it any harder than that 
5: I personally did an 8.25 swap in my car and would do it again. Even the u-joint was the same size.


What axle is right for you? That depends. I'll lay out the pros and cons of each below.

Dana 35:
Pros: Easiest swap. The axle tube is the same size, so the Eagle u-bolt plates and be reused. These also do not have the longer pinion snout, so the driveshaft will not have to be modified. It will also be the easiest one to find. Closest to the stock Eagle rear end.
Cons: It is the weakest unit of the three that I listed. There were two styles: one with c-clips and one without c-clips. The change happened sometime around 1990. Neither are very good. I personally would not do this swap. I do not believe that the ease outweighs the weakness of the axle.

Dana 44:
Pros: Its strong. Dana 44s are used in new Wranglers and were found in a lot of trucks from the 60s-90s. I would also call it the most "correct" upgrade since they were found in Jeeps from the same era that the Eagle was in production.
Cons: These things are expensive, I looked for one for 3 years and never found a reasonable one. They are also expensive. Most I've seen have gone for $400-$600. You will need different u-bolt plates as the axle tube is larger. The pinion snout is 1" longer, so your driveshaft may need to be shortened.

Chrysler 8.25:
Pros: Plentiful, these came in a lot of Cherokees from the mid 90s-2001. They aren't that expensive either. I picked mine up for $75 and it came with wheels and a front axle. It looks very similar to a Dana 35, so many people cannot tell them apart. If you're building a sleeper Eagle, this may be a good option if you want your car to look stock underneath. These were available in 27 and 29 spline. Before 1997, all 8.25s were 27 spline. Starting in 1997, all 8.25s were 29 spline. The 29 spline is better, but either are an upgrade. Almost as strong as a D44 for a fraction of the price. This will live behind a mild V8 or stroker I6.
Cons: You will need different u-bolt plates as the axle tube is larger. The pinion snout is 1" longer, so your driveshaft may need to be shortened. It isn't period correct. These came out in the 90s, years after Eagle production ended.

Why not just swap in a Ford 8.8?
My Dad built a YJ with an Explorer 8.8 and my Comanche has an Explorer Sport-Trac 8.8. They are great axles, however they do have some drawbacks.
Pros: They are strong and plentiful. IIRC, the Sport-Trac one is a little bit wider than the Eagle rear end, so it will make the track width almost the same as the front. Some 8.8s had disc brakes.
Cons: Most 8.8s (exception being the Sport-Trac) is narrower than the stock rear end. The center section is very large. You need 35" tall tires on an 8.8 to have as much clearance as a vehicle with 31s on a D35. The driveshaft flange is different. Every single bracket will need to be cut off and replaced. The highest gear ratio commonly found in 8.8s is 3.55. The highest gear ratio in a Sport-Trac (the only 8.8 I'd recommend for an Eagle) is 3.73.


What I did and Why:
For my Eagle, I chose the Chrysler 8.25 with 3.54 gears. I did have to regear the front to match, but that was part of the reasoning behind changing the axle. I wanted lower gears. I chose the 8.25 because it is strong and it was cheap. From my prior research along with sale prices I've seen for these axles, the 8.25 has D35 pricing and D44 strength.

Would I change anything?
The only thing I would change would be getting some shims to get the pinion angle a little bit better. Other than that, I am very happy with the swap and I would do it again. The 3.54 gears seem perfect behind the 258, even though I do not have overdrive. If a person does a lot of highway driving, I'd recommend 3.08 gears. With 3.54 gears and 225/75R15s, you are turning roughly 3,000 rpms at 70. I've had my car up to 80 briefly and it was completely fine.