Custom Long Arm XJ Suspension

XJ with standard control arms.

My basic plan was to shorten a set of the Rubicon Express TJ  LCA and use the Rubicon adjustable upper arms that I already had on my jeep.  The longer LCA that Rubicon sells are 36" long, but due to the XJ's engine/transmission placement I had to cut the arms down and have them rewelded so that they were 33" long.  I decided to build a large "belly pan" out of 1/4" steel that would serve two purposes, one as the mounts for my new LCA and the second as a skid plate that would protect my transmission and transfer case.  To eliminate the annoying drive shaft vibrations I was having I called up Tom Wood and had him sent me his Slip Yoke Eliminator kit (SYE) and custom length CV drive shafts for the front and rear. 

One of the biggest problems with building onto the XJ is its lack of a solid frame.  Since the introduction of the downsized Cherokee in '84 they have all been built with a unibody type of frame.  This design uses thin metal frame rails that are welded to the body allowing the shell of the jeep to give support and rigidity to the rails.  Unibody equipped vehicles are great for fuel economy and weight savings but they lack the strength that a normal frame provides.  I have almost completed my degree in Mechanical Engineering and I have a pretty solid background in stress analysis and load distribution so I spent some time pondering over the best way to support my new sub-frame.  With the help of a 3D modeling program I was able to come up with several designs that would work.My first thought was to weld sleeves horizontally into the unibody rails and then run bolts through them, but since I do not have the skills that are required to weld onto the unibody I knew that option was out.  The method that I chose involved utilizing the factory cross member mounts in addition to making a few mounting points of my own.   In order to distribute the load properly and make the sub-frame very rigid and heavy duty I used a total of 6 bolts per side spanning 24" along the unibody rails.  

click on the photo to see an enlarged photo of the new crossmember

For the first three bolts I drilled and tapped the original factory cross member inserts for 1/2" bolts instead of using the smaller and weaker metric threads that were original there.  For the back three bolts (closer to the rear axle) I fabricated a nut strip that slid into a slot I cut in the unibody rails.  The nut strip is simply a piece of 1/2" thick bar stock about 14" long that I drilled and tapped in three spots for the mounting bolts.  I decided to go this route instead of using threaded rivets (nut-serts) because they are prone to pull out of the metal under heavy load.  This way the skid plate and the nut strip would sandwich the frame rails and keep it from pulling away.  I also fabricated two spacers out of 2"x2" heavy walled square tubing that would run the length of the skid plate and space it away from the frame a bit. 

All of the components used to build this custom suspension

This added clearance was needed for the transmission/transfer case mount and for the LCA mounts.  I knew that this would decrease my ground clearance some but overall it still sits higher than the factory cross member did.  I made the LCA mounts from heavy gauge angle iron and bolted them to the belly pan with 1/2" grade 8 bolts.  I used grade 8 bolts on the entire project because the last thing I want to happen when I am climbing a steep rock ledge or running down the highway at 70 mph is for one of the bolts to shear off.   After getting lots of feedback from the XJ-list I decided to use a set of coil springs that I bought from Rusty's Off-Road.  I chose these springs because they have a soft spring rate and with the addition of a 1" spacer I am now sitting comfortably about 6.5" higher than stock. 

click on the photo to see an enlarged photo of the new crossmember

I originally had a set of Trailmaster coils that were fairly stiff and gave me a rough ride on the road even with my RS9000 shocks set on 1 or 2.  I figured that while I was changing things I might as well replace my worn out and noisy RE sway bar disconnects with a set of the new JKS 2^nd generation disconnects. The last and probably most important component to this setup is the shocks.  I went with a set of long travel RS9000s because I wanted the ability to adjust the valving the way I wanted it.  I tried to get the longest travel shocks that would fit so that I could utilize the flex that the new control arms would allow.  This can be difficult using the factory stud/eye configuration so in order to get the right shocks I needed to convert the upper stud mount to an eye mount with a bracket that I bought from Rubicon Express. 

Cutting off the factory control arm mounts. No turning back now.

Installing the components was the easy part it was making them that was the most time consuming.  The only thing that had to be done that was rather intimidating was cutting the factory lower control arm mounts off.  This step signified the point of no return and once they were gone there would be no going back to the factory system.  The mounts had to be cut off to allow the new arms room to move as the suspension cycled.  While everything was off I also took the time to undercoat everything with Herculiner.  This is another product that I was very impressed with and I think it will hold up really well to the abuse it is going to experience.  I also installed the SYE and drive shafts that Tom Wood sent me.  Once the SYE was installed it was basically a matter of bolting up the new CV drive shaft and shimming the rear axle so that the pinion angle was right.   The remaining part of the installation was just bolting up the belly pan, control arms, front drive shaft, shocks, springs and sway bar disconnnects. 

After removing the mounts and Herculiner

Longarm length vs standard arm

Will it work?  That is the question I kept repeating over and over as I pulled out of my garage and onto the street for the moment of truth.  After several test drives and adjustments I got it dialed in and it now works exceptionally well.  The soft springs and almost horizontal LCA make my XJ ride better than it ever has.  The harsh pounding that I would feel every time I hit a bump is gone and now I can go over railroad tracks without fear of my rear view mirror falling off.  The small bumps are now almost non-existent and the bigger ones are soaked up smoothly and easily. 

Longarms installed

One thing I have noticed is that when hitting big dips in the road the suspension will compress almost to the bumpstops which causes the steering to feel a little "loose".  This is due to the way the new arms change the castor angle as they move through their range of motion.  This is really only noticeable at extreme flex which usually occurs on the trail going 2 mph where the castor angle really has no impact.   The best thing about this modification is that it has improved my on road ride as well as the off-road performance instead of sacrificing one for the other.  However, I will caution that this type of project is not for everyone and I would strongly recommend that if you research and plan your ideas before doing any cutting or welding.  Changing the factory suspension and/or steering can be extremely dangerous if it is not done correctly, so make sure that you know what you are getting into before you start.   If you have any questions feel free to email me at hbtcob@hotmail.com.

Finished product