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Choosing the right donor XJ


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I have a 1988 SWB 4.0 2-WD with an AW4 tranny and I'm currently searching for a donor xj to do a 4x4 swap.  I intend on staying with an automatic transmission.  Would prefer to find a xj with a 30 and 8.25 and swap both of them in.  I'm aware that I would need to move perches on the 8.25 if I did so.  So my question is:  Do I need to find a Renix era XJ to swap (Pre 1990), or will a 91-96 swap just as easily?  I have exhausted the search option and still do not have a real clear understanding as to what else would be involved if I used components off a 91-96.  Teach me some knowledge people!

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The 8.25 was never offered in a Renix era MJ/XJ.  So, you will have to search for a 93+ XJ to get the 8.25.

 

The D30 was offered throughout the MJ XJ line.

 

An AW4 from any year 4.0 XJ will bolt up to the MJ.  

 

Assuming you buy a complete 4wd XJ, you'll get the matching tcase....you know the rest (spline count differences on the tcase).

 

You will need to have the rear drive shaft made to fit the MJ.  The XJ D.S. will not be the proper length for the MJ.  

 

The front D.S. is a direct swap.

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39 minutes ago, Amccutc21 said:

I am aware the 8.25 was never offered in renix era xjs. My main concern is ease of the swap.  Would it be any more involved if I didn't get a renix donor?

 

Not if all you want are the axles and transfer case.

 

Beyond that, everything is different. Related, but different.

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the link in my sig should have some writeups on swapping in the later AW4s.

97+ 8.25s are the good ones.  the 8.25 from a Liberty is even better (slightly wider and comes with disks)

every year XJ could still have the dana 35 under it so verify before purchase.  

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Yet again a recommendation for the 03+ KJ liberty rear end for the swap. Disk brakes and the cables should be compatible with your MJ parking brake setup. Overall about as easy as it gets. 

 

For trans mission and transfer case I'd recommend 96+. The 96+ has a different rear seal in the xfer case and it will not leak fluid if the drive shaft is removed. 

 

For front axle the 99 was the last year of the HP, so I'd take the newest you can find in the best condition. 

 

Make sure your gear ratios match. 

 

You can find parts from multiple vehicles and probably wind up with a better setup than trying to find one donor vehicle. 

 

 

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With regards to 8.25's, the ones out of the early HO's are only 27-spline axle shafts, which are smaller and weaker (read not much of a step up from a d35 if any) than the later beefier 29-spline versions. 

Making the gear ratios match is also a big deal when you're looking at picking up parts from multiple vehicles. KJ axles are mostly 3.73's, 4.10's in a 4-cyl, but you can't pull a matching front axle because they're IFS. XJ's did come with both ratios but not frequently, so finding a matching axle at a wrecking yard may not be easy. I believe the d30's in ZJ's and WJ's will bolt in and are likely to be had in 3.73's but you'll want to double check that, plus they're low-pinion so that's a thing to think about as well. In my case I found a 4.10 KJ 8.25 with discs and then it was two and a half years before I picked up a high-pinion 4.10 d30 to match that was within my budget, and then it was still a 1000-mile round trip to go get it... But it also came with a matching MJ AMC20 rear axle, so go figure.

As to the compatibility of newer AW4's, this thread over at NAXJA should help: http://www.naxja.org/forum/showthread.php?t=1053970

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4 minutes ago, gogmorgo said:

With regards to 8.25's, the ones out of the early HO's are only 27-spline axle shafts, which are smaller and weaker (read not much of a step up from a d35 if any) than the later beefier 29-spline versions.

 

Much depends on what you plan to use the MJ for, and how you drive. The early 27-spline 8.25 axle shafts aren't enough better than the Dana 35 to be worth arguing, BUT ... the Dana 35 has smaller and thinner axle tubes, and Dana 35s fail more frequently due to the tubes bending than they do from simple shaft failure. That said, I still have Dana 35s under both my '88 XJ and the '88 MJ that I wheeled with NAXJA-NAC. The XJ I ran on 30s, and I ran 31s under the MJ when I wheeled it. Both vehicles have been all over Paragon (when it was open). But I'm a wimpy wheeler -- I don't drive with a lead foot.

 

The later 8.25s are significantly better than the early ones, but IMHO even the 27-spline 8.25 is a step up from the Dana 35.

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On 2/15/2018 at 7:46 PM, Sir Sam said:

Here is a video I took showing some of the info for the KJ rear axle swap.

 

Great video, Sam! On the Liberty rearends, what is it (dana 44) and what ratios were offered? Also, I may have missed it but who makes those spring perches? They look well made and I really like how the Ubolts are out of harm’s way (center pin looks vulnerable though.)

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Amccutc21 - Thanks for asking this.   It's confirmed the direction I'm heading in.   I have a 1988 SWB 4.0 2-WD with an AW4 too and am planning to convert to 4WD this spring/summer.   I'm primarily using a 1995 XJ for parts.   

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1 hour ago, Kickin’Chicken said:

Great video, Sam! On the Liberty rearends, what is it (dana 44) and what ratios were offered? Also, I may have missed it but who makes those spring perches? They look well made and I really like how the Ubolts are out of harm’s way (center pin looks vulnerable though.)

 

Libertys have a 29 spline 8.25 and the common ratios are 3.55/3.73 with 4.10 being offered on some 4bangers.

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When swapping in a later 4WD AW4 to replace your 2WD AW4 and using your original harness, there will be some pin-out differences in the TCU connector as it changed several times throughout the years. So be sure to mach the wiring by wire function (not color), or you might end up with no torque converter lock or no O/D.    Example:

5a88513fb57b7_TCUConnector.jpg.5a73a5dd3484290dead58dbde58eedb9.jpg

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2 hours ago, Kickin’Chicken said:

Thanks, Pete! Do any of them come with factory limited slip?

 

Limited slip was an option in all Jeep rear axles. Anything you find in a junkyard may or may not have a limited slip. And Jeep's limited slip is a clutch type, so even if a junkyard axle has it, it may or may not be worn out.

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2 hours ago, Kickin’Chicken said:

Thanks, Pete! Do any of them come with factory limited slip?

 

Yes you can find them with LSD. ALL KJ diesels sold in the us had 3.73 LSD rears. 

 

KJs are pretty common in the pick n pull junkyards here, and people also part them on Craigslist. 

 

Car-part.com would be a good resource to look for one near you too, but verify the gear ratios and LSD before purchase. 

 

Ruff stuff is the maker of the spring under kit I bought. Open my video on YouTube and it's in a playlist, part one shows a little more of the swap and there are a few talking about the springs I used as well. 

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4 hours ago, Pete M said:

 

Libertys have a 29 spline 8.25 and the common ratios are 3.55/3.73 with 4.10 being offered on some 4bangers.

Right. I forgot the later manual v6's came with 3.55's. The chances of finding a manual KJ in a yard up here are pretty slim. 

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2 hours ago, Eagle said:

 

Limited slip was an option in all Jeep rear axles. Anything you find in a junkyard may or may not have a limited slip. And Jeep's limited slip is a clutch type, so even if a junkyard axle has it, it may or may not be worn out.

Thanks. Sam said all the diesels had them so that what I'm gonna look for. 

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1 hour ago, Sir Sam said:

 

Yes you can find them with LSD. ALL KJ diesels sold in the us had 3.73 LSD rears. 

 

KJs are pretty common in the pick n pull junkyards here, and people also part them on Craigslist. 

 

Car-part.com would be a good resource to look for one near you too, but verify the gear ratios and LSD before purchase. 

 

Ruff stuff is the maker of the spring under kit I bought. Open my video on YouTube and it's in a playlist, part one shows a little more of the swap and there are a few talking about the springs I used as well. 

Thanks again, Sam! Just like the advice you have on the '98-'99 xj engine harness and ecm, looks like you're dead on the money (again!)

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1 hour ago, Kickin’Chicken said:

Thanks. Sam said all the diesels had them so that what I'm gonna look for. 

 

your chance of finding one is sliiiiiiiiimmmmmmm to none.  they only made 12000 total on this side of the pond. 

 

car-part.com lists axles by ratios so it's easy to choose what you want to search for. :thumbsup:  

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2 hours ago, Kickin’Chicken said:

Thanks. Sam said all the diesels had them so that what I'm gonna look for. 

 

Honestly don't bother......I was just saying that IF you found a KJ diesel being parted that it originally came with the LSD.

 

I went on car-part for your area and started looking at options, there are a fair number from regular junkyards around with 3.73s and varying prices.

 

Also note that the KK liberty and dodge nitro have the same rear end, but only in 3.21 and 3.73, but I don't know how different other things may be on it. The KJ and KK are VERY similar vehicles, so its likely one of those would work for you.

 

However think through what front axle you will get.

 

XJs that you want to get your front axle from will likely have 3.55s. 3.73s are basically no existent in XJs and in HP d30s.

 

So if you got 3.73s in your rear end then you would need to purchase a set of 3.73s for the front. Also IIRC the 3.73 LSD will not work with 4.10s.

 

Just consider the cost of hassle of either regearing a front or regearing a rear.

 

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No guarantees Joe Blow at the yard got the ratio correct either when putting it into their inventory, either, although it is a good indication. What would be better to look for is a v6/auto combo if you want the 3.73's or v6/manual if you want the 3.55's. Or a 4-banger if you want the 4.10's. But it's far easier to find a 3.55 ratio d30, pretty much every automatic XJ had them (with a few exceptions but not many).

You should be able to tell if a KJ has a Trac-loc by the axle tag, or alternatively if you can get online from the yard, go here:

https://www.jeep.com/webselfservice/jeep/index.html?screenName=customer&country=us&emailUrl=goToEmailForm%28%27R%27%29

hit "equipment listing" in the left column, and plug vins in until you find one with Trac-loc. 

I discovered that tool while looking to see if there was a code on a glovebox sticker or something that would indicate the trac-loc the way GM's G80 code works, but no such luck. But I like that tool. Says you shouldn't use it for vehicles prior to '98, when Chrysler required digital input of their files, but the source I got it from says you may get lucky so I plugged in my MJ's VIN... Apparently I have the "southwest edition" that must feature the "door armrest storage lamp"... I guess the AMC option codes don't translate well at Chrysler, lol. 

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