Modified XJ Cherokee Tech XJ (84-01)
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Coil spring expert advice needed

Old 08-27-2015, 02:31 PM
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Default Coil spring expert advice needed

I have a 97 XJ & a 91 MJ that are both running 33's.

The XJ has RE 3.5" coil springs and ACOS to achieve just over 5.5" of lift.

The MJ has RE 4.5" coil springs and .75" poly coil spacers to achieve just over 5" of lift.

The MJ rides much more harsh than the XJ. At the time I lifted the MJ, I did some research into various coil springs and read that the RE 4.5" springs were softer than most 4.5" springs on the market. I am beginning to think the info I relied upon was wrong. My XJ rides like a dream...the MJ is just much stiffer.

Also, both the XJ & MJ have Rocky Road control arm drop brackets & the control arms in both vehicles are at a very minimal slope. In fact, since the MJ has less lift, the control arms have less slope which should improve the ride. The XJ has RE Monotubes & the MJ has Bilstein 5100's. The XJ does have a winch which adds some weight to the nose and may improve ride a tad, but aside from that, the fronts are set up very much the same.

The harshness in ride is definitely coming from the front end.

Does anyone have a list of 3.5"-4.5" coil spring rates? I really like the fine tuning capability of ACOS in the XJ, so I'm ok with a spring that offers less lift and adding ACOS to the MJ as well. My main goal is to soften the ride. I've heard great things about the ride of OME springs, but I don't know anyone personally that has used them.

Any first-hand advise is welcome.
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Old 08-27-2015, 03:03 PM
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Right off the Rubicon express website:
http://www.rubiconexpress.com/Lift-K...6&vgID=12#tab1

RE1300 Front 3.5"240 lbs/in
RE1310 Front 4.5"164 lbs/in
RE1345 Front 5.5" XJ/ 4.5" ZJ184 lbs/in
RE1358 Front 7.5"213 lbs/in

another reason for a large difference in the ride quality between vehicles could be the valving between the shocks. The Rubicon Express monotubes are built by Bilstien but to different specs. Billstein builds their shocks to their specs and RE has Bilstein build them to RE specs. That may be a large contributing factor to this.
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Old 08-27-2015, 03:58 PM
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Same accessories on both front ends?
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Old 08-27-2015, 04:03 PM
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Originally Posted by weswins View Post
another reason for a large difference in the ride quality between vehicles could be the valving between the shocks. The Rubicon Express monotubes are built by Bilstien but to different specs. Billstein builds their shocks to their specs and RE has Bilstein build them to RE specs. That may be a large contributing factor to this.
From those specs the 4.5" springs should ride much softer. You may be right...maybe the front shocks are causing the stiffness.

Maybe I'll swap a pair of RE mono-tubes onto the MJ and see if it makes a difference. Swapping shocks is easy enough. The ones on the XJ are 7 years old & starting to rust. I suppose if they don't help the MJ's ride the XJ can use the new shocks.
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Old 08-27-2015, 04:10 PM
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Originally Posted by SeriousOffroad View Post
Same accessories on both front ends?
They are set up essentially the same. Almost identical CAD, both have adjustable upper & lower control arms. Axles positioned pretty much alike. Same caster, etc. The MJ drives & tracks straight...no problems there. It just takes bumps, potholes & bad pavement a lot rougher than the XJ. As a matter of fact, the ride in the XJ is quite impressive. It is silky smooth. In the MJ, I approach railroad tracks with dread.
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Old 08-27-2015, 09:56 PM
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Default Coil spring expert advice needed

Same tires? It could be attributed to shocks. If you know the model number on the Bilsteins you can check what theyre valved at. As stated the RE shocks are valved to RE specs and supposed to match the vehicle application. You also cant discount the extra weight from the winch. Swap the shocks though I am interested in hearing how that turns out. Id like to have a bit softer ride up front. I also have RE 4.5" coils, RRO CADs and 5100s but I wouldnt say my ride is harsh at all.
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Old 08-28-2015, 08:47 AM
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XJ has 33x12.50 R15 Cooper STT's. MJ has 33x12.50 R15 Mickey Thompson MTZ's. Both are ultimately made by Cooper. Both are mounted on aluminum 15x8 wheels. I run 28-30 psi in both on the street.

On a side note, The Great Smoky Mountain Jeep Invasion will be held about 15 miles from where I live tomorrow. There will be lots of vendors there, including Rubicon Express. Maybe I'll be able to pic the brains of their reps...or at least get them to tell me if the RE shocks are valved significantly different from the Bilsteins.
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Old 08-28-2015, 09:00 AM
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I'm running a 4 1/2" lift on my XJ based on a Rustys 3" full leaf/coil package using 1 1/2" Boomerang Shackles and the ACOS with the 3" HD coils for a winch/bumper combo but he also offers another softer coil for a stock front end XJ as well. I run Bilstein 5100's and the ride quality is very good on/off road you might have a look.
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Old 08-28-2015, 10:01 AM
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I went through a similar experience with the exception that both vehicles were XJ's and both riding on Bilstein 5100's. One a '97 and the other a '98. Otherwise, both had the exact same parts replaced with OEM or better.

The '97 rode better/smoother and I couldn't figure out why. The '98 was/is in much better shape all around. Or so I thought...

I replaced the upper/lower ball-joints and the wheel hubs/bearings on the '98 and it instantly rode/handled better than the identically built '97.

This may not be the issue with your's, but it can't hurt to check them if you're going to be swapping shocks.

BTW, I was running the Rusty's 3" HD's on both at that time and I did not like them for what I was building the XJ's for. They were too soft. (sorry Fred. Lol) I switched the '98 to RE 3.5" coils and liked the ride/handling much better. Installing RRO CAD's took it to a whole other level.
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Old 08-28-2015, 11:28 AM
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Originally Posted by 4WD4EVER View Post
I went through a similar experience with the exception that both vehicles were XJ's and both riding on Bilstein 5100's. One a '97 and the other a '98. Otherwise, both had the exact same parts replaced with OEM or better.

The '97 rode better/smoother and I couldn't figure out why. The '98 was/is in much better shape all around. Or so I thought...

I replaced the upper/lower ball-joints and the wheel hubs/bearings on the '98 and it instantly rode/handled better than the identically built '97.

This may not be the issue with your's, but it can't hurt to check them if you're going to be swapping shocks.

BTW, I was running the Rusty's 3" HD's on both at that time and I did not like them for what I was building the XJ's for. They were too soft. (sorry Fred. Lol) I switched the '98 to RE 3.5" coils and liked the ride/handling much better. Installing RRO CAD's took it to a whole other level.

Were you quite heavy in the front? My winch bumper is light weight one a tube and winch weigh's 100#. I was concerned about the final ride height also and it was fine with the 3" kit at the time and still holds the same height now bumped to 4 1/2".
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Old 08-28-2015, 12:18 PM
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No, no weight on either unit. I honestly never could figure it out. Wish I could have. Lol! Too much "bounce" or "hop" to the wheels is the best I can explain it and a significant amount of diagnostic time/money in parts was spent on the problem with no satisfaction.

I went to the RE 3.5"s out of sheer frustration/curiosity and the heavier rate and it worked out for me. The ride is light-years better.

I don't know if it matters, but my builds see mostly street/high-speed highway/light-trail use and most streets/highways here in Texas are in good condition. I needed something that would function well under those conditions.
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Old 08-28-2015, 12:44 PM
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Originally Posted by 4WD4EVER View Post
I replaced the upper/lower ball-joints and the wheel hubs/bearings on the '98 and it instantly rode/handled better than the identically built '97.
The front axles on both then XJ & the MJ are completely rebuilt. When I regeard them I replaced the ball joints with Moog parts on both. The control arms, drag link, trac bar & tie rod ends are all also new on the MJ.

The truck drives & tracks just fine, but I cannot understand why it rides so much stiffer than a comparably built XJ. It's not that it is awful...it's just that it rides very stiff and the XJ rides great.
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Old 08-28-2015, 02:00 PM
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Understood ahenderl. You helped me out once in a PM I had sent you quite some time ago. Just thought if I could return the favor in some way I would. Let us know if you ever figure it out.
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Old 09-01-2015, 05:11 PM
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RE had a rep at the Smoky Mtn Jeep Invasion this weekend. While he wasn't an expert on XJ/MJ set-ups (I think the bulk of their business is centered around JK's & TJ's), he did say that the RE shocks are made by Bilstein but are made to RE's specs.

I called RE today and spoke with a guy in tech support. He confirmed that the RE Monotubes are in fact made by Bilstein and are much softer than the standard Bilstein 5100's.

I am going to order a pair of RE Monotubes for the front and will post what I find out.

BTW, the 5100's that are in the front of my MJ are Bilstein part # 24-188197 which looks to be exactly what all of the catalog companies are selling for TJ/XJ/MJ with 4"-6" of lift.

The more I think about it, the more I think that the MJ doesn't ride that bad...it's just that the XJ is sooo much better and I am hoping to get the MJ to ride the same.
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Old 09-01-2015, 06:02 PM
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Hey, thanks for posting that! If you're really bent on getting the MJ to respond in a more favorable way and you have the coin, you may consider a set of progressive rate springs and/or front shocks w/ different valving.
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