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Using An Xj As A Cheap Drive-train Overhall?

Discussion in 'Intermediate CJ-5/6/7/8' started by Stephen Gillett, Dec 18, 2017.

  1. Dec 18, 2017
    Stephen Gillett

    Stephen Gillett New Member

    Connecticut
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    Hello!

    I've been musing as to how to give my '72 some better manners on the highway and there are a few key items that come to mind for improvement: Suspension, Power, Track width. My plans for this jeep include light trail runs and summer cruising.

    I'm in the process of solving for suspension with the Rocky Road kit, my mind wanders as to affordable ways of solving for power and track width. It occurs to me that buying a cheap, rusty XJ might kill both birds with one stone.

    Why do this? Cheap XJ's are almost free once you've pulled what you need and parted out the rest. One-stop shopping; as you'll read below, I intend to use nearly the whole buffalo

    I'm looking at XJ's right now in the 500-1000 range that are running, driving, stopping rust buckets. It's well accepted, and my personal experience supports the fact, that the 4.0 ax15 NP231 combination is robust and dependable as drive lines go. If buying the correct year XJ, you can also grab an HP dana 30 front and 29 spline Chryco 8.25 rear. Given that my plans for this jeep are trail runs and fun summer cruising on 33" tires, those axels should be more than sufficient if properly maintained.

    Drive line Potential Concerns
    The obvious issues with the engine/tranny/xcase: 1. Motor mounts need to be moved 2. Wiring can be complicated 3. the AX15 is a comparatively long transmission, fit/drive shaft angle could be an issue. Responses as follows: 1. I would probably need to move motor mounts for any engine swap, though I am really hoping that someone will tell me that since the 258 was available at the same time as the 304, AMC had the good sense to standardize the placement of the mounts on the frame (I highly doubt this is the case). 2. I've swapped in three 4.0 HO engines to date in older CJs and YJs, I've wired all of them, I've never had an issue. 3. I have a CJ6, same wheel base (104") as the XJ.

    Positive Counterpoints
    Good reasons to use this driveline combo: Very reliable and strong from the factory, personal familiarity with this combo (I've rebuilt a 4.0, a 231, and have had three ax15's that never needed rebuilding), enormous aftermarket support, AX15 and 231 are strong enough for use behind an SBC V8 if I chose to go that route at some point in the future.

    Axles Potential Concerns
    The obvious issue/likely comments with these axles are as follows: 1. The front is set up for coils, the rear is set up for spring over, 2. The drop is on the wrong side 3. I'd need new wheels to accommodate the 5x4.5 pattern. To point 1, i'm pretty handy with a grinder and have welder who works for beer. Unless i'm missing something, I am not intimidated by cutting off coil buckets and CA mounts and having new perches welded in place. To point 2, if swapping in a 231, the drop lines up. To point 3, if you buy the entire XJ, you get wheels that match your axles. What am I missing here?

    Positive Counterpoints
    Dramatic increase in track width/stability, HP dana 30 and Chryco 8.25 are decent axles for my intended driving style, considerable aftermarket upgrades (though not overwhelming).

    I ask that you politely pick apart my argument.
     
  2. Dec 18, 2017
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    Medford Mass USA
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    JMO - the '72 has some pretty good axles already. The two ratios that were available are 3.73 and 4.27 optional, and you are unlikely to better those from a stock XJ. The 4 cyl XJs came with 4.10s IIRC, but that's not what you are considering. Track width is easy - I'm running 7" Soft 8s with 33x10.5R15 KM2s with 2.5" backspacing, vs. the factory 3.75". I have plastic flares, and with more width than that I probably would not pass safety inspection.

    I'd also go with an automatic. 3.73s with a 700/4L60 would be a nice combination, and you could even go to say 4.54s if you were willing to regear. Driving an automatic on the trail is a different style, with one foot on the throttle and the other on the brake, and you don't need nearly the reduction as you do with a manual.

    If I were considering this, I would skip the XJ and look for a Chevy V8 with a passenger drop NP241C (87-98 Blazers, Burbs and Tahoes). Then I could keep the factory axles and suspension and wheels and tires ... at least until the next stage of modification. I don't see much advantage to the XJ drivetrain unless you already have a 232/258 and want to swap in the 4.0L HO. I predict that the fuel economy wouldn't be much different.

    What's wrong with the 304? I'm a bit surprised that you'd want more power than the 304 can deliver. Re the 4.0L HO, the Chryco (Bosch? pretty sure it's Bosch) MPI is a great system, but the engine is an antiquated pushrod OHV just like the 304. Plenty of ways to get EFI on the 304, if that's what you want. It's never going to an economy car, but I predict you'll never make back the added expense of a complete drive train swap from a hobby car. And wow, what you propose is a big project. Pop a AX15 or NP3550 in there and be proud. Go Dana 300. Go TBI 304. Unlike a CJ-5, you have the room for a 5-speed. ... unless you want an automatic.
     
    Last edited: Dec 18, 2017
  3. Dec 18, 2017
    Daryl

    Daryl Sponsor

    Bonney Lake, WA
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    1. The stock axles in a intermediate CJ are superior in every way to XJ axles.
    2. A stock 72-75 CJ in it's stock form is the most capable combination of CJ that was ever made.
    With a set of BDS springs and shocks and everything in good condition these are a really nice platform.
     
    Last edited: Dec 18, 2017
  4. Dec 18, 2017
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    I would note - this is a CJ-6 so I suspect he has room for the XJ transmission and transfer case.
     
    Last edited: Dec 18, 2017
  5. Dec 18, 2017
    Stephen Gillett

    Stephen Gillett New Member

    Connecticut
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    Hi all,

    Thanks for the responses, much appreciated. My reasoning behind the XJ axles is that they are considerably wider than what I'm running currently. I'm installing an Old Man Emu 3 inch lift as part of my suspension refresh which has me thinking that I will want some extra width to keep me from being too tippy. I agree that the axles I have at present are strong and up to the task, but they are rather narrow. As I'm sure Timgr will acknowledge, those of us living in New England are sometimes required to hit the freeway for a bit before we can hit the dirt, wider axles would serve better in both circumstances.

    As to the choice of the 304 or the 4.0, my inclination there is familiarity and reliability. I'm quite used to the 4.0 providing low maintenance power that's plenty enough for for most open-topped jeeps. The fact that it's already injected simplifies things, I have bad memories of my 258 coughing and sputtering when off camber and that has me worried that the 304 will perform similarly. That said, my 304 runs wonderfully at the moment down the road, though it has been difficult to do any proper testing at high way speed because my suspension was in such bad shape.

    Timgr, your signature suggests you have some experience running a 304 in front of t15, care to advise me on how well it should run in the 45-60 mph range?
     
  6. Dec 18, 2017
    ITLKSEZ

    ITLKSEZ Hope for the best, prepare for the worst

    Liberty Lake, WA
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    I say go for it, if you're willing to accept the little things that will be easy to overlook at first glance.

    Fuel supply will either get expensive or creative: incorporating the XJ pump into your tank, building a custom tank to accept the pump, or buying the parts pre-made to use a pump outside of your tank...
    Wiring is the same deal. You say you've done this in the past, so it looks like you know what you're in for.
    The front axle might be more work than you plan. I believe the pumpkin is further from center than on a CJ, so it might force you to outboard your front springs.
    The 4.0 is a long engine; make sure you are prepared for the headaches of placement. Not just in the engine bay, but also where the front axle lines up in relation to oil pan clearance, unless you will be running enough lift for that to be a non-issue. This holds especially true with the HP front axle.

    The XJ/YJ axles were designed to use deep-dish wheels to eat up some of the axle width, and to keep the scrub radius in check. If you use wheels with "standard" backspacing, it is going to add another few inches of width to an already wide setup, and handling might suffer. Make sure you'll be able to legally roll down the road with a minimum of 4 extra inches of tire hanging out each side. I know the east coast isn't too fond of that.
     
  7. Dec 18, 2017
    Daryl

    Daryl Sponsor

    Bonney Lake, WA
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    I guess the reason I am usually against builds like this is that over the years I have bought dozens of Jeeps that have gone down a similar path. They almost never are finished to the point where they are driveable. Then I come along, pay pennies on the dollar for them, harvest any sellable parts and scrap the hulk of another Jeep that will never again drive down the road. It is your Jeep and you can do anything you like to it. I would say that before cutting up a drivable Jeep, PLEASE write down your plan, make a realistic budget for what the true cost of finishing it will truly be and be honest with yourself about the probability of success is.
     
    47v6, timgr and ITLKSEZ like this.
  8. Dec 18, 2017
    ITLKSEZ

    ITLKSEZ Hope for the best, prepare for the worst

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    And don't sell any of the parts to "fund" the build. If it goes horribly and nothing works as planned, you can always go back to stock.
     
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  9. Dec 18, 2017
    Stephen Gillett

    Stephen Gillett New Member

    Connecticut
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    Thanks again for the comments. Daryl, I hear you. I've seen buddies end up selling well-meant, poorly planned projects in the past. To give you an idea, my last swap was a 4.0 AW4 242 out of a XJ into a YJ with 258 ax15 231. From writing my own wiring diagrams 10 times over to clocking the xcase, to reworking fuel delivery with an external pump and regulator, there was a lot of planning. At the end, everything worked as expected.

    ITLKSEZ- point taken about the pumpkin placement, thanks for the flag.

    Question: If my goal is to widen my stance so that i'm less tippy on the road/ when going through turns, am I over thinking this instead of just looking to add a sway bar to limit my body roll?
     
  10. Dec 18, 2017
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    I've had 2 CJs and my J10 with a T-15. It's a great transmission, for a 3-speed. Not sure why you are asking about the 45-60 range. Is there something about that speed range that has worried you? I have found the T-15 to be a very good all-around transmission. Are you concerned about the engine speed, second gear downshift, or what?

    You can wear out the second gear blocking ring if you try. Replacing blocking rings is fairly easy, though you need to take the transmission apart. It's a strong transmission - came standard with the 360 in J20s in the 70s, and I don't recall any breakage.
     
  11. Dec 18, 2017
    Stephen Gillett

    Stephen Gillett New Member

    Connecticut
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    Mostly concerned about engine speed when traveling on the highway. I know that the 3rd in the t15 is 1:1, just wondering if that doesn't leave me running the 304 pretty hard to maintain speed. This concern is what has me looking for something with overdrive.
     
  12. Dec 18, 2017
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    Mmm. Just drive it. I used to drive my '73 with 4.27 axles on the California freeways and kept up with traffic. I regularly drove a couple hundred miles from LA area to the desert on the interstates and back with no issues. I drove it from LA to the Grand Canyon and back several times. No problem. AMC put the 304 in TransAm cars and ran it at racing speeds.

    [​IMG]

    The AMC V8s will get very low hot idle oil pressure when they are worn out. At that point, you are risking hammering a rod bearing, but a healthy 304 will be fine at highway speeds. As long as you've got good oil pressure, just drive it.
     
    Last edited: Dec 18, 2017
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  13. Dec 18, 2017
    tarry99

    tarry99 Member

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    Been done several times before..........your older body will probably need some surgery to lower the body down onto the new XJ frame that is wider overall from front to back.
     
  14. Dec 18, 2017
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    :confused:

    An XJ does not have a frame, IIRC. F/R live axles, coils front, leaf springs back, unibody between. Maybe you are thinking Wrangler?
     
  15. Dec 18, 2017
    tarry99

    tarry99 Member

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    Thanks Tim.........Yep...........Maybe I did not say that correctly........as I've seen guys cut the insides out of there CJ's to drop them over what's left of that unibody / chassis / sheetmetal where the mounts are more outboard.....
     
  16. Dec 18, 2017
    sterlclan

    sterlclan Member 2022 Sponsor

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    fwiw the 4.0 shares the same motor mounts as the 258 and the 304...
     
  17. Dec 19, 2017
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    Not exactly. The 4.0L will drop on the the 258 mounts. The intermediate left mount is the same, but the right mount is different between the V8 and six.
     
  18. Dec 19, 2017
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    I would also note that I replaced the '73 with a '75 CJ-6 with a 258 and T-14. Same 1:1 final drive ratio, 3.73 axles. For a while I worked in Irvine and lived in Santa Monica, and drove the 405 freeway about 50 miles each way. No problem on the highway. I even got speeding tickets.

    If everything is in good condition, any CJ drivetrain combination from '72 up is fully highway capable. If you don't feel at ease at moderate highway speeds, something is wrong.
     
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  19. Dec 19, 2017
    sterlclan

    sterlclan Member 2022 Sponsor

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    Mine musta been the oddball the 304 bolted right in.
     
  20. Dec 19, 2017
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    It's a different part number according to the book. It even has a different drawing in the parts book. Pretty sure we've been through this before.

    It would be interesting to compare ... I'll pull the cover off of my '75 and photograph/measure if someone with a 258 can do the same.
     
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