Jeep Liberty 8 1/4 rear swap

Transmissions and Rear Ends

  1. Idle Ender

    Idle Ender Well-Known Member

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    It seems a few of you are interested in the details of this swap so I figured Id write up a bit of a walkthrough. I have no record of any measurements or anything, so this is more of a proof of concept. It can, in fact, be done for less than $400. Bear in mind that none of these pictures were taken with replicating the process in mind. Mostly just to post on Facebook and whine about how much of a pain in the ass it was during the whole 6 month adventure. Some background information; this 80 Volare is my daily. Slant 6 auto with 70k miles and dead reliable. Never planned to drag my deathtrap of a project S10 (LS swap in the works, 2.8 with a brake leak, super loose front end, and no power steering) out of the garage, but I had to. I had only anticipated driving it for about a month while I slapped the Plymouth back together, but other projects stretched that into 6 months. One day the 7 1/4 started dragging and banging around turns. Seeing how I NEVER checked and/or changed the fluid in it, I wasnt all too surprised. Figured Id nab an 8 1/4 and upgrade while I was at it. After some research, I settled on an 8 1/4 out of a Liberty with disk brakes and 3.73s. If I did it again, Id hunt down one with limited slip, but this rear was minty with zero rust and brand new brakes. It might have been easier to find a bolt up replacement out of another F-body, but this deep in the rust belt these cars are nowhere to be seen.
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    First step was to remove all of the old mounting hardware. I mean ALL of it. nothing swaps over and theres a lot of junk welded/bolted the axle. Torches, hammers, and lots of grinding. The end result was a rear axle that was near identical to a 8 1/4 from the 70s. (Minus the disks)

    Before:
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    After:
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    The next step was to weld on the new 3" axle spring perches. Measure the width center-to-center of your old perches and use that measurement on the new one. Keep in mind that the 8 1/4 pumpkin is offset to one side unlike the 7 1/4. I measured from the backing plate on both sides to make sure they were even.
    20160523_203047[1].jpg

    After that, I went to work grinding down the calipers to fit under my 14" wheels. To clarify, 15" wheels SHOULD clear them. I just like my wheels. Plus I just put new tires on them and am broke af. I also rattlecanned it to seal it all up and make it look decent.
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    Now to clean up all the old mounting hardware. I just wire wheeled most of the rust off mine to save cash, but I plan on buying an isoclamp delete when I put new 5 leaf springs and a sway bar under it. I initially planned to do all of it to begin with, but money held me back. All I could afford was new rubber and shocks. Bolt everything up! I used a motorcycle jack to roll it under. Highly recommend it. It should all bolt up exactly like the factory if your measurements are correct. Currently in the process of custom bending some rear brake line and adding a prop valve just in case. The ghetto clamped stock lines function perfectly, just look like crap. SIDE NOTE: DO NOT CUT BRAKE LINE FROM AXLE TO BODY ON NEW AXLE TO GET IT FROM A JUNKER! Mopar charges like $300 for that short line and theres no aftermarket solution. I work at a Ford/Mopar dealer and I couldnt get one for less. I cut mine without realizing it was a problem and ended up having to go back to the yard and grab one.
    20161030_145229_HDR[1].jpg
    DO NOT CUT THIS LINE!
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    Last big hurdle was the driveshaft. Grab the one from the Liberty since youll need it. Mine came with the newer bolt on yoke, but not all do. Also, the newer Jeep diff has 29 splines over the 27 of the older diffs. The Jeep driveshaft and the F-body driveshaft have different size U-joints, so keep that in mind if you custom order a driveshaft to lenth. Im a cheap-ass, so my solution was to cut the old Plymouth shaft to length (1.6" off if I remember correctly), weld the Jeep end to it, and hope that it didnt vibrate to pieces. So far its been very smooth, but well see. A new one is always an option.
    20161222_190218[1].jpg

    Last step is to fix the speedo and its done! Im at this stage right now. Finding a gear with the teeth I needed in the F-body style was impossible so I swapped to the older metal housing that you can get gears for. Currently waiting on the cable and itll be buttoned up and back on the road.
    20161224_151548[1].jpg

    Any questions?
     
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  2. Justwondering

    Justwondering Well-Known Member

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  3. 89.Fifth

    89.Fifth Well-Known Member

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    That's awesome. Do you have a link to bigger pics?

    How hard was it to setup the rear brakes?
     
  4. Idle Ender

    Idle Ender Well-Known Member

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    Thanks! Ill make a photobucket album of all of it when I get home from work. I have some more pictures, too.

    It wasnt hard at all. The new brake line threads into the pre-existing line. If I had 15" wheels, I wouldnt have had to touch the brakes at all.
     
  5. BudW

    BudW Moderator Staff Member

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    A good write up!
    I need to get Jeep differential measurements, so I can add them onto my chart.

    I looked at some random year Jeep Liberty’s.
    2002 had a choice of 8¼” or Dana 35. Both look the same at first glance but most parts will not interchange. All ‘02’s were drum brakes. Gear choices are 3.73 and 4.10 with an option of limited slip.

    Spring perches will need to be welded onto diff on bottom. If existing spring perches are in same location, they could be left on (not sure why one would want to) and shock brackets will need to be cut off.
    02 Liberty.PNG


    2005 are all 8¼” are all with rear disk brakes. Gear choices are 3.55, 3.73 and 4.10 with option of limited slip.
    There is a lot of extra brackets to cut off and new perches will need to be welded onto it.
    05 Liberty.PNG


    2008 is much like the ’05 version, but gear choices are only 3.73 and 4.10. There was no option for limited slip, in ’08.
    08 Liberty.PNG


    I wanted to add a few points for others thinking about attempting the same swap.
    These items may have been done by Idle Ender (I’m not sure, but will assume he did).

    A /6 might not need this, but any engine making more than stock power will need to have a pinion snubber on it (ie: really for any V-8).
    20170112_084652.jpg
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    All of the 8¼”s I’ve seen has had bosses ground for a snubber, but all of the pickups I’ve seen (can’t say for Jeeps, but would assume the same) didn’t have screw holes drilled or tapped – so fairly easy job to do. All you would need is a pinion snubber and reuse old bolts.

    Guess what, 7¼” and 8¼” pinion snubbers are different (the rubber generally is the same). I would think a person could make one using some thick plate steel.

    Now you are thinking “why do I need one”?
    Under hard acceleration, the front of differential will want to go the opposite direction the tire is turning (up in this case) and this is what is referred to axle windup. What happens is the pinion snubber makes contact with floorboard which keeps that motion in check.
    Again, you might be wondering “why do I need one, still”?
    What happens is the Universal Joint (U-Joint for short) is at an odd angle with power applied to it, it greatly reduces the life expectancy of the U-joint and in extreme cases, U-Joint breakage.

    Think the wobble joint in your socket set. Yes they help in many cases, but other times they are not helpful at all. Your propeller shaft is the same thing as a socket set wobble joint. They prefer only a small amount of movement or “bad things” happen (mainly pre-mature U-Joint failure).

    The next thing to think about is driveline angles (propeller shaft and U-Joint angles). This is from my '77 FSM.
    PS Angle 1.PNG
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    contuned ...
     
  6. BudW

    BudW Moderator Staff Member

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    PS Angle 6.PNG

    The rear Yoke splines are the same and will interchange with the flat flange version.
    Yoke.PNG

    I recommend reusing your old yoke (from your 7¼”), but that is my opinion.

    You will be installing a new pinion and axle seals before installing your used differential into your car, are you not?

    BudW
     
  7. Idle Ender

    Idle Ender Well-Known Member

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    Thanks for the more technical information, Bud! It would have been a lot more long winded if I had tried to explain every little step. Lol. That and some I had forgotten. That older style rear looks like it would have been quite a bit easier to strip down! Oh well. It was worth it for the brakes. I had intended on putting the bumper or "snubber" on for the reason you described. As you said, the 7 1/4 doesnt fit. So in the scrap pile it went. A stock slant can go without it. When it gets the turbo, Ill rig up a bumper using the existing bolt holes. Also, I kinda eyeballed the pinion angle rather than actually measuring. The stock angle is slightly downward but almost straight so it was pretty easy to fudge. Good enough for a 90ish HP cruiser. Definitely a point you want to pay attention to, though. Off by too much and youre asking for vibration and U-joints going bad.
     
  8. Idle Ender

    Idle Ender Well-Known Member

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    The bolt on yoke ended up working fine, but its really a matter of preference at that point. The idea was to try to get it together without needing to tear down the rear at all. Faster and cheaper. The one I found was extremely low miles and had just been put on the yard, so I trust it not to leak. I just changed the fluid and cover gasket and popped her on. Of course, if it had been in rougher shape I would have replaced all the seals beforehand. I didnt even put on new U-joints. Lol. Although I probably will in the near futue.

    Dont get me wrong. If I had to do it again and time/money werent an issue seals, better measurements, new u-joints, a "snubber", keeping the old yoke, new springs, new brackets, and less rigging up parts would be ideal. The end result ended up working out, thankfully. Of course, all of these things can still be done after the fact. Chances are that they will. But for now Im just happy being able to drive it again.
     
    Last edited: Jan 12, 2017
  9. BudW

    BudW Moderator Staff Member

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    The reason I wrote that I did, is if your example works out, this might be a very workable solution to many of us. Making a step by step instructions can only be helpful for others.

    Like you said, it is not a true bolt in. I was giving additional items to think about, for those thinking about it.

    Personally, I like the older yoke only because U-Joint replacement is faster (if/when needed) and shortening a shaft vs. adding a new end to it, makes the propeller shaft more manageable.
    Either style will work fine.

    It would be my luck the new shaft would be larger in diameter than original one is, taking that option off of the plate.
    Murphy has to stick his law in there, somewhere.
    BudW
     
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  10. Idle Ender

    Idle Ender Well-Known Member

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    Very true. The more information, the better.

    Btw. Just hooked my cable up and tested it with the speedo sitting in my lap. Its only 1 mph off from my gps. Perfect. Id feed it through and put my dash back together, but its in the teens outside. Lol
     
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  11. rcmaniac791

    rcmaniac791 Well-Known Member

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    This is awesome. Thanks for the write-up. I may be looking into doing this swap someday. As for now, I enjoy getting 25+ MPG on the highway, so I'll stick with the 7 1/4
     
  12. mopops

    mopops Well-Known Member

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    with the jeep center section offset from center --- the original rears being in the center how does that work out?
     
  13. Idle Ender

    Idle Ender Well-Known Member

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    The offset doesnt effect it too much. When making the driveshaft I just had to take the extra inch or so extra length to the side into account.
     
  14. mopops

    mopops Well-Known Member

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    i have a chance to get a 93 ranger 8.8 2wd rear end -- the center section offset is about 2" do you think that is too much?
     
  15. Idle Ender

    Idle Ender Well-Known Member

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    I couldnt tell you for sure. The Jeep rear isnt offset nearly as much as a Ford 8.8, but you could probably get it to work. lol. People pop those in everything.
     
  16. 84Furyus

    84Furyus Well-Known Member

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    Thanks for the info. May look into this as my 7.25 isn't going to last long behind the 318 that's making more than stock power.
     
  17. BudW

    BudW Moderator Staff Member

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    For Chrysler vehicles made from ’60's to present (this doesn't apply to front differentials or those with IRS (Independent Rear Suspension)) – all differentials use the same width (or length, not sure which term to use) axle shaft.
    Now with that said, the cars older than FMJ’s do have different mounting between the Left and Right sides. The axle length might be the same but because of the way axles mount to differential, they might not be interchangeable.
    FMJ’s axles are interchangeable Left to Right, so don’t have that problem).

    One thing I haven’t measured is where the differential yoke is in relation to being centered in the differential (or not). I would suspect the differential yoke is dead center – but sense I haven’t measured it, I can’t say for sure.


    Something most people don’t know about is the engine/transmission is parallel to the centerline of car, but is not in the exact center (centerline) of the car. I don’t know the amount of engine/transmission offset is but would guess to be about 2 inches offset to passenger side of the car. If you were to take a straight edge and place on inner side of frame rail and measure one side to (pick a location, like say the edge of engine valve cover) and do the same on other side using the same locations, and you will see I’m correct.

    The propeller shaft is off-center to the passenger side of car and is offset horizontally to reduce vibration. I’m guessing that amount to be about 2” (5 cm). If a person was to install a differential that is already 2” offset, there might be a chance of additional driveline vibration (maybe). Propeller shaft length will also be a bit different, but will it be enough to matter?
    BudW