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A few comments on RC 4.5" long arm setup


NAXJA Forum User
As part of a front axle swap, I completely disassembled the RC 4.5" long arm front suspension on my XJ, and then put it back together with a few changes. A couple of comments on optimizing the setup:

-- Switching from a fully linked radius arm to using just one short arm (on the driver side) greatly increases the flex compliance of the front suspension. Easily can tell the difference even on the highway. I know I've already mentioned this in another thread, but figured I'd consolidate it here.

-- There is room to make the long arms 1/2" longer than specified by RC. This increases tire clearance to the back of the fender well. A few mods are needed. First is that the sway bar needs to moved forward to keep from hitting the springs. Second is that the rib on the back of the RC track bar mount needs to be trimmed to provide clearance to the coil springs.

-- No front (or rear) bump stops are provided. RE1380 2" bump stops do the job for the front and are cheap.

-- The primary interference point during full flex is the driver side coil spring perch on the axle hitting the track bar mount. If the axle is centered at ride height, these pieces will collide a few inches before reaching the true limit (where the long arm hits the unibody rail). This happens because the RC track bar mount is really long. Its 1/2" longer than any other's I've found. Even with the axle shifted over to the driver side to make room, there is still some chance of collision because the track bar bushings are so squishy which can allow the axle to shift. Trimming the track bar mount along with shifting the axle slightly is the driver side is the most reasonable solution. There are no issues when flexing the passenger side to full compression.

-- The track bar bushings are very squishy. My solution was to install OEM JK track bar bushings that are set up to use 9/16" bolts. Requires slightly opening the holes in the track bar and of course drilling the mounting points for 9/16" bolts. Still some squish with these but a lot less than the RC bushings, and now I have 9/16" bolts at both ends.
Does the track bar bracket hit the axle because it drops so low? Does it ever hit the pumpkin or only the coil mounts

It only hits the driver side coil spring perch. Everything else clears no problem, even with the axle pushed forward 1/2". This is because a radius arm suspension rotates (tilts back) the axle significantly as it goes through the available travel.

The only other potential issue I see is coil spring contortion at full compression. I only assessed component interference and coil spring accommodation without the coils installed. The tilt-back of the axle points the base of the coil spring fairly far back. I don't know if this will cause issues with the coil springs rubbing or hitting nearby suspension components. I intend to try to flex out the front suspension with it assembled, so I should eventually have a better idea of whether the coils can handle the challenging axle tilt and forward position.

I've been driving around for a few days now with the sway bar disconnected (because the sway bar will hit the coils if its connected to the axle), and the front suspension compliance is excellent. I want to bag radius arm suspensions because its not an ideal approach, but with it set-up as a pseudo 3-link without the sway bar connected, its super smooth and handles fine on the street for a lifted vehicle.