t_long

DISCLAIMER: This thread is a work in progress. I will add pictures later, but I wanted to post the majority of the info now. Also, I wanted to put it in the Write-Ups section, but I don't have access. Mods, if you think it's worthy, let me know. Thanks.
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Well, my 99 XJ is officially back up and operational with a 31-Spline Ford 8.8 rear axle under it. I’ve still got bugs to work out, but I drove it to work today, so that’s progress. Since I just got it back up and running last night (for the first time in nearly 3 weeks), I thought I would do a little post-mortem and talk about some of the lessons that I learned the hard way and never saw in anyone’s write up.

I’ve read a number of write-ups where people say they finished this in a day or a weekend, and I would say those people must either be really good mechanics or were really focused on getting this done quickly. I wanted to make sure everything was done right. This was my first axle swap and I did 99.5% of the work solo. My total time investment in the work (fit up, paint, welding, brakes, etc.) is probably somewhere in the ballpark of 150 hours. There were a few other projects I did in conjunction with this, but I will get to that later. Treat this as food for thought in case you’re thinking this swap is no big deal. Yes, it can be done faster, but it all depends on how you work.

First, I’ll quickly answer the “Why’d you do it” piece. Let me just say that I went from a 29-Spline Chrysler 8.25 to an 8.8. A lot of people will say that this swap is frivolous and for someone just looking for a project, but the up sides were a lot bigger than that for me, personally. I bought my 8.8 from a guy in Northern California. It was about a 1,000 mile round trip (from San Diego). You might still be thinking that I’m insane, but I enjoyed the adventure of going up there too. Here’s why I traveled the distance:

• I bought the axle from a guy (actually off the forum here) who had intended to put it under his Jeep, but sold the Jeep before he did. He’d bought everything brand new other than the housing, shafts, spider gears and carrier.
• DISC BRAKES (this was big for me)- new calipers, pads and Rotors. I knew I would be wanting to swap to discs in the future, so an 8.8 was killing 2 birds with 1 stone.
• The 8.8 was freshly, professionally geared to 4.88 which is the ratio I wanted and all of the bearings and seals were done at the same time (master install kit)
• New Ruff Stuff install kit and diff cover
• New soft brake lines from (I think) East Coast Gear Supply
• New brackets and hardware for the hard and soft brake lines
• Factory LSD - better than open, currently unsure if I’m going to lock it down the road, but I’ve loved getting on the skinny pedal in the corners so far
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Things I didn’t read before starting on this swap:

What to do with the old axle while the 8.8 was in work

Thankfully, I already had an extended brake line going to the distribution block in the rear. This allowed me to place the old axle on the ground (under the rear door area) with everything still hooked up. Since the brakes were basically the last thing I hooked up, my 8.25 spent good portion of the project time with both the main brake line and E-Brake lines still connected. I’d recommend you consider how long it’ll be before the swap is complete before fully detaching your brake lines (either that or buy a plug fitting). After my 8.8 was initially mocked up, I put the 8.25 back in the Jeep and drove for a couple days while I was working on the 8.8.

Drilling the U Bolt Plates
As my info says, I have a 4.5” RC lift. Hate or love them and their products, that’s what I have. The centering pin on the leaf springs has a pretty large nut on it (I wanna say the hole needed ended up being 7/8”). Significantly larger than the hole on the U Bolt plates shipped by Ruff Stuff. The best way to tackle this is with a drill press, but I don’t have one. So what I did was use a step up drill bit and plenty of oil. As some of you probably know, drilling through ¼” steel is no easy task. This took some time and patience.

Spring Perches Wouldn’t Straddle the Axle Tubes
If you’re anything like me, you might not like “modifying” something that was newly purchased for a specific application. When I started the project, I was scratching my head because the spring perches from Ruff Stuff wouldn’t completely wrap around the axle tube because they had of these little protrusions at the ends of the arc where the axle tube was supposed to be. I ended up grinding the 2 bumps at the end off and leaving the one in the middle so the gap could be filled.

Brake Line Bracket Location
The soft brake lines I got required a few small brackets to be welded to the axle so to be held in place. I welded them up with the U bolts in place no problem. Once I got to final reassembly, I learned that I had welded the brackets too close to the U Bolts on one side, and therefore the line wasn’t able to go through the bracket straight.

Hard Line Routing / Cutting
Quick pro tip: You will need 2 hard brake lines. One is roughly 8” and the other is roughly 34”. I bought my lines at O’Reiley, and they only sell 40” lines. Borrow the brake line flaring tool while you are there and save yourself a second trip. You will also need a tube cutting tool of some sort. The auto parts store should sell them.

Brake Line Fitting
The fitting on the soft line I got from ECGS was too large to meet up with the one coming out of the Jeep’s unibody. Check this before you rip the brake system apart.

E-Brake Cables
You CAN use your D35 or 8.25 E-Brake cables if you want to put in the work. Yes, you will save some money, but you will need to disassemble the drums on the rear axle to get the disconnected. By the time I got to this point, I was tired of being stuck on the minor things, so I cut them with an angle grinder.

Crush Washers
Your soft brake lines will require 2 copper crush washers on each side (4 total). One of those goes between the bolt head and the brake line block and the other goes between the caliper and the brake line block. GET NEW ONES FROM THE START. My Ford dealer said the washers were discontinued, but the ones I got from O’Reiley worked out just fine.

I tried re-using old ones (and I only had 1 per side) and the system leaked like you wouldn’t believe. Then I ended up stripping the head of the bolt trying to tighten the line to the caliper to stop the leak. With this in mind, just start with what you need from the beginning.

Spider Gears
During final re-assembly, the spider gears fell out of my axle when I was trying to align the hole in the carrier with the hole in the center of the spider gears. Getting them back in was a BEAR. It took me at least 5 hours. That said, be advised: if you turn the axles without the cross pin in, your spider gears will fall out once they reach a certain point. Try aligning the holes another way. If this happens to you and you can’t get it figured out, PM me and I’ll help you out.

The Width Difference
I’ve read things saying that the width difference is anywhere between 5/8” and 1.5”. Who to believe, I don’t know. I will say though, that I feel the width difference is noticeable, and I plan to run some spacers to compensate for it. Also, I’m running 33” x 12.5” tires with 15” x 8” wheels and 3.5” backspacing and they come pretty close to the springs. Keep this in mind because you might need to do something about that if you’re running higher backspacing with similar tires.

Welding the Shock Tabs
I will be doing the shock tabs twice. My Ruff Stuff install kit came with these tabs, and they aren’t the right ones. Zone sells some that resemble the stock setup but better. Buy those for your XJ. For the time being (because I can’t go any longer without shocks) I’m going to reweld mine at the correct angle for the shocks to be wider on the axle and still fit correctly. It’ll eat a set of lower shock bushings, but meh.
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Projects I did in conjunction with this swap:

Shortening my t-case output shaft again:
After finishing my HnT SYE, my driveshaft was uncomfortably close to fully collapsed. I took the opportunity to re-cut and re-tap my t-case output shaft and shorten the IRO yoke slightly. The driveshaft length looks a little better now.

Shackle Re-relocation
After installing relocators and boomerang shackles, my ride height in the rear was a little high for my liking. However, in order to move the shackles up to the upper holes, I needed to trim the relocation brackets significantly. This is what mine look like now. They’re HD Offroad No Lift relocators.
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Things I still need to work out:

Re-bleeding the brakes
As I’ve said, this took a long long time and all I wanted was to test drive the thing when I was done. I bled the rear brakes and went with it. As a result, my pedal isn’t perfect but it’s functional. I will re-bleed them when I install my ZJ proportioning valve.

ZJ Proportioning Valve
There is an article on this if you google it. The guy makes it seem like no big deal, but re-bending the bracket on the ZJ proportioning valve is a pain. I worked on it for a little before giving up and deciding I would do it later. I do, however, still feel a huge improvement in stopping power. It’s definitely confidence-inspiring.

Driveline Vibrations:
I got a JY drive shaft and replaced the U-Joints in it. Since finishing the install, the jeep vibrates pretty good at right about 45 mph. The cause could be the new DS, possibly the HnT Yoke that I recut or driveline angles. I haven’t had time to search it out as of yet.

xjcherokeeblog.blogspot

Thank you so much for this write up! I knew it wasn't easy but I hear people saying they do it in a day like you said. I think I'm going to rethink swapping mine out now until I have a week off.

extrashaky

Yes, thanks for the write-up. I have an 8.8 sitting in my garage waiting for me to get busy on it, so this is relevant to my interests.

Skittle

Good write up...

But a couple things.

1. Don't remove your stock prop. Valve. Just remove the large screw on it and swap the guts (spring, o-ring, etc.) Like you said... Its no big deal. Takes about 5 minutes to swap with no brake line issues.

2. The perches do fit properly. The tabs are meant so the same perches fit on a smaller axle. For the 8.8, your supposed to grind them off like you did.

3. No matter what you say, it shouldn't take that long to drill through 1/4" plate. Go at a slow speed for big bits. I cut through with a 5/8" bit from a 1/2" hole in about 15 seconds.

4. When you install the spider gears, align both of them in the axle gears, but 90° from where they should be (aka, blocking the view you would normally have into the carrier). Then rotate till they line up with the cross pin hole. First time, it took me 5 minutes lol

I'm just adding this stuff because it makes the job seem a lot harder than it actually is. 5 hours for the spider gears is way too long lol

Other than that, good job. The first time doing a real project always takes way too long lol.

t_long

Just making my contribution to the forum here, man... Your superior mechanical knowledge would have been useful BEFORE I finished the swap, like when I posted a thread asking what I should do about my shock tabs. Thanks for the great feedback though. I'm not going to bother replying to each of your points.

andrewmp6

Something else to think about is a yukon ultimate 88 axle kit,You get to lose the c clips better axles and it widens the width a inch pre side putting it back around the xj width.

jazarra

this thread just saved me i didnt have those pesky washers and when i went to bleed brakes i was shocked to see all the leakage