My 2005 LJ Rubicon has a 4.5" Rock Crawler X-factor lift kit, which was installed by the PO. When the PO purchased the kit, he had recently had the exhaust upgraded and had installed onboard air with the tank mounted under the belly. Both the exhaust and the air tank were in the way of installing the long rear upper control arms, so instead of relocating these, he purchased the long arm kit with just the short rear uppers, which he installed with the long arm kit. Later on he purchased the long arms with the intention of rerouting the exhaust and relocating the air tank, but he never got around to it and the uninstalled long rear upper control arms came with the jeep when I purchased it. I was doing some inspection the other day and noticed that the control arm bushings on the rear uppers are in need of replacement.
If I'm going to replace the bushings, might as well take the opportunity upgrade the short arms to the long arms, right? But the more I think about it, there is a decent amount or work to reroute the tail pipe and relocate the air tank. Enough to the analyze the situation anyway. Here are my thoughts, please correct me if I seem to be misguided.
Flex and articulation: My first reaction is you would increase the articulation ability with the long arms as they would have more travel and the geometry is designed for the 4-link triangulation of the long arms together. But as I think more about it, with the truss bringing the upper arm mounts to the center of the axle above the pumpkin, that changes things a bit.
The length of the control arm will determine the amount of vertical distance the axle can travel. The center of the rear axle doesn't strike me as a spot that would benefit a lot from vertical travel as the articulation is at the tires is much more important. That stated, I think the benefit of more articulation with the longer arms would be minimal.
Geometry: I am lacking in expertise when it comes to suspension geometry and pinion angles, but here is my uneducated assessment: With the existing frame bracket location further towards the rear, the angle of the short arms becomes more perpendicular to the frame. The upper control arms are now the only thing keeping my axle squarely centered under the Jeep, so when going around a corner, the arms are putting a lot of sideways force on the bushings, rather than front to back force. I think this is why these bushings wore out so much quicker than the others. If I were to install the long arms, the bracket is now directly over top of the lower, allowing for full travel and reducing the sideways force on the bushings. At the same time, if the upper control arms are shorter than the lowers, as the suspension travels up and down there will be a variance in the pinion angle. If the control arms are the same length then the pinion angle remains constant. Not really sure if this is true, or if it even matters, but something I thought about. Here’s a sketch to demonstrate this thought.
Essentially I am trying to determine which of these is better and if it’s worth the work to accomplish.
Let me know what ya think, thanks!
If I'm going to replace the bushings, might as well take the opportunity upgrade the short arms to the long arms, right? But the more I think about it, there is a decent amount or work to reroute the tail pipe and relocate the air tank. Enough to the analyze the situation anyway. Here are my thoughts, please correct me if I seem to be misguided.
Flex and articulation: My first reaction is you would increase the articulation ability with the long arms as they would have more travel and the geometry is designed for the 4-link triangulation of the long arms together. But as I think more about it, with the truss bringing the upper arm mounts to the center of the axle above the pumpkin, that changes things a bit.
The length of the control arm will determine the amount of vertical distance the axle can travel. The center of the rear axle doesn't strike me as a spot that would benefit a lot from vertical travel as the articulation is at the tires is much more important. That stated, I think the benefit of more articulation with the longer arms would be minimal.
Geometry: I am lacking in expertise when it comes to suspension geometry and pinion angles, but here is my uneducated assessment: With the existing frame bracket location further towards the rear, the angle of the short arms becomes more perpendicular to the frame. The upper control arms are now the only thing keeping my axle squarely centered under the Jeep, so when going around a corner, the arms are putting a lot of sideways force on the bushings, rather than front to back force. I think this is why these bushings wore out so much quicker than the others. If I were to install the long arms, the bracket is now directly over top of the lower, allowing for full travel and reducing the sideways force on the bushings. At the same time, if the upper control arms are shorter than the lowers, as the suspension travels up and down there will be a variance in the pinion angle. If the control arms are the same length then the pinion angle remains constant. Not really sure if this is true, or if it even matters, but something I thought about. Here’s a sketch to demonstrate this thought.
Essentially I am trying to determine which of these is better and if it’s worth the work to accomplish.
Let me know what ya think, thanks!
