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Hey everyone I was wondering if some of you can help shed a little light on this subject for me and my specific situation. I have checked all the major threads regarding caster and alingnment for my xj but still am a little unsure about a few things. So I bought this jeep with about an 8in lift in the front. The springs where sagging and shot so I when and grabbed a set of new rusty's 8.5's. Now when I purchased this jeep the caster was way outta wack when the old springs where still on. The pinion angle was almost parallel with the ground.... Once I got my new springs and shocks in my lift was raised a fair amount causing the caster to worsen. So I went ahead and adjusted the uca and got the pinion closer to where it needs to be. I would like to get the angle better but I am not sure how far I should take it considering the way my coils are starting to bend. I have part time 4wd with a posi lock on my d30. So vibes at high speeds wouldn't nessesaraly be an issue for me as my front ds only spins when I am in the dirt at lower speeds. I have read everywhere and most people consider pinion angle to be priority. My question is: should I get the pinion angle straight with the tc or find a good medium between caster and pinion angle? And also how my springs will be affected due to the change in caster and if the arch in the springs are acceptable. Thanks in advance!
Here are some pics :
My pinion angle as it sits right now after I adjusted my uppers
Here's the bend in the spring, not sure if that's acceptable or if it could go some more to achieve proper pinion angle
General rule of thumb is to sacrifice only as much caster as is needed to eliminate front driveline vibes due to pinion angle.
More in depth info:
Ideally, you want the pinion yoke to point to the TC output yoke because the double cardan joint takes care of the driveshaft angle. if the u-joint at the pinion end operates at an angle, there is no other u-joint to compensate for it. This is a pretty simplified description of the issue, but for the purposes of this discussion it suffices.
Caster angle affects how your steering behaves. HAve you noticed how after making a turn, when you let go of the steering wheel it has a tendency to want to self-centre? That's a result of caster angle.
As caster angle reduces, the system's ability to self-centre is reduced as well so that you have to help it do so. Also, straight line stability is compromised and you may find that the vehicle tends to wander more.
With respect to your springs bowing forward:
This happens because as you rotate the axle housing forward to compensate for your pinion angle, the lower spring perches also start to pitch forward. This is logical as the perches are attached to the axle housing. The more you have to rotate the axle forward, the more that everything (spring mounts, shock mounts, swaybar mounts, lower track bar mount, etc.) will start to deviate from their most neutral position. That's just how it goes. The fix is either reduce the lift or cut apart the axle housing so you can clock the differential but keep everything else where it needs to be.
In addition to that, because of the amount of lift you have and your control arm angle, as your suspension compresses your axle actually has to move forward as it moves up. This, of course, moves the lower spring perch forward which, in turn, forces the bottom of the spring forward.
Basically, there are a lot of forces at work fighting each other in your front suspension. I can't imagine that the ride is particularly enjoyable.
I'm not a long-arm fan, myself. I'm running in the neightbourhood of 5" of lift with Rubicon Express adjustable short arms and drop brackets and my lower control arms are almost parallel to the ground. But if you are intent on keeping your lift at that height I'd suggest that you might want to explore long arms as an option to getting back some compliance in your front suspension.
I also see from your pic that you are not running a front anti-sway bar and I can't tell if you're running a track bar. On coil springs you should at the very least, run the track bar. Better yet is to keep the sway bar as well. Coil springs have far less lateral stability that leaf springs do (think of a slinky and how you can move it around) so you need the track bar to keep the axle positioned under the vehicle. Coil springs also have no internal friction the way leaf springs do so they are more compliant (depending on spring rates) than a leaf spring in the same application. In other words, coil sprung vehicles are a little more prone to body roll than that same vehicle on leaf springs.
To give you an idea of the importance of swaybars and track bars: When designing a suspension system, suspension engineers follow a heirarchy; an order of importance or priority in terms of what considerations/components are more or less critical than the others. In order from most important to least hat is:
1) geometry
2) swaybars
3) springs
4) shocks
They follow this heirarchy because they do not want to design a system where a subordinate component has to compensate for the shortcoming of a superior component. ie: using springs to compensate for poor geometry. The fact that swaybars are the secondary consideration should be an indication of how important they are.
In a nutshell, with the amount of lift that you are running, I would advise you to talk to someone very experienced in suspension design in order to gain a better understanding of why suspension systems and components are designed the way they are and what their optimal operating ranges are. With 8"+ of lift, there are very very few, if any, out of the box, bolt on systems that address all of the issues properly. You're into custom fabrication territory.
General rule of thumb is to sacrifice only as much caster as is needed to eliminate front driveline vibes due to pinion angle.
More in depth info:
Ideally, you want the pinion yoke to point to the TC output yoke because the double cardan joint takes care of the driveshaft angle. if the u-joint at the pinion end operates at an angle, there is no other u-joint to compensate for it. This is a pretty simplified description of the issue, but for the purposes of this discussion it suffices.
Caster angle affects how your steering behaves. HAve you noticed how after making a turn, when you let go of the steering wheel it has a tendency to want to self-centre? That's a result of caster angle.
As caster angle reduces, the system's ability to self-centre is reduced as well so that you have to help it do so. Also, straight line stability is compromised and you may find that the vehicle tends to wander more.
With respect to your springs bowing forward:
This happens because as you rotate the axle housing forward to compensate for your pinion angle, the lower spring perches also start to pitch forward. This is logical as the perches are attached to the axle housing. The more you have to rotate the axle forward, the more that everything (spring mounts, shock mounts, swaybar mounts, lower track bar mount, etc.) will start to deviate from their most neutral position. That's just how it goes. The fix is either reduce the lift or cut apart the axle housing so you can clock the differential but keep everything else where it needs to be.
In addition to that, because of the amount of lift you have and your control arm angle, as your suspension compresses your axle actually has to move forward as it moves up. This, of course, moves the lower spring perch forward which, in turn, forces the bottom of the spring forward.
Basically, there are a lot of forces at work fighting each other in your front suspension. I can't imagine that the ride is particularly enjoyable.
I'm not a long-arm fan, myself. I'm running in the neightbourhood of 5" of lift with Rubicon Express adjustable short arms and drop brackets and my lower control arms are almost parallel to the ground. But if you are intent on keeping your lift at that height I'd suggest that you might want to explore long arms as an option to getting back some compliance in your front suspension.
I also see from your pic that you are not running a front anti-sway bar and I can't tell if you're running a track bar. On coil springs you should at the very least, run the track bar. Better yet is to keep the sway bar as well. Coil springs have far less lateral stability that leaf springs do (think of a slinky and how you can move it around) so you need the track bar to keep the axle positioned under the vehicle. Coil springs also have no internal friction the way leaf springs do so they are more compliant (depending on spring rates) than a leaf spring in the same application. In other words, coil sprung vehicles are a little more prone to body roll than that same vehicle on leaf springs.
To give you an idea of the importance of swaybars and track bars: When designing a suspension system, suspension engineers follow a heirarchy; an order of importance or priority in terms of what considerations/components are more or less critical than the others. In order from most important to least hat is:
1) geometry
2) swaybars
3) springs
4) shocks
They follow this heirarchy because they do not want to design a system where a subordinate component has to compensate for the shortcoming of a superior component. ie: using springs to compensate for poor geometry. The fact that swaybars are the secondary consideration should be an indication of how important they are.
In a nutshell, with the amount of lift that you are running, I would advise you to talk to someone very experienced in suspension design in order to gain a better understanding of why suspension systems and components are designed the way they are and what their optimal operating ranges are. With 8"+ of lift, there are very very few, if any, out of the box, bolt on systems that address all of the issues properly. You're into custom fabrication territory.
Thank you for the detailed response regarding all the issues I am dealing with. I do plan on adding a sway bar and sometime in the future I will defiantly go to long arms. Also I am running a RE adjustable trac bar. After I adjusted the caster I did the "redneck" alignment for the time being. I am taking my rig to a alignment shop here in SoCal that specializes in lifted jeeps. I am also running ruggid ridge HD steering with a drop pitman arm. So it will be nice to hear what this specialized alignment shop will have to say about the geometry of everything. I know an over the knuckle kit would be the right way to go with this setup and will possibly upgrade in the future but I am going one step at a time lol
Axles to far forward bump stop should be same angle as spring. Hard to draw straight but you get the idea.
I have both upper and lower control arms adjusted the same on both sides. The wheel looks centered in the wheel well but I could be wrong. On the passenger side the bumpstop is centered and on the drivers side is close to rubing. From what I can tell it seems that the bumpstop tower is slightly bent. I know this can be a common occurrence with xjs. I'll know more after I get it professionally alingned this Friday.
FYI. From the factory, there is a 10mm difference in wheelbase. Shorter on passenger side. This could have something to do with the difference you are seeing.
If you have someone else do the alignment, I strongly suggest it be done at a 4x4 shop, not a tire shop or regular garage.
FYI. From the factory, there is a 10mm difference in wheelbase. Shorter on passenger side. This could have something to do with the difference you are seeing.
If you have someone else do the alignment, I strongly suggest it be done at a 4x4 shop, not a tire shop or regular garage.
Find local clubs theres always an alignment tech/tire guy. I get mine done by a jeep guy at a shop $50 and he adjusts and readjusts everything. Last time he had it on and off the rack 3 times.
Thanks again for all this good info guys. I haven't posted much cause I have been swamped at work and haven't had time to work on the jeep. So I took my jeep here in socal to an off road alignment shop called clarks house of suspension. They were extremely helpful and the ride is much smoother and the wheel returns to center much better. I am still have a few concerns regarding my steering. My next purchase is gonna have to be a swaybar. Freeway on ramps are sketchy to say the least. My steering is also very sensitive and small motions will jerk the jeep side to side. I know a sway bar will help remedy this situation, but my question is: is the steering also very sensitive because the drag link u joints are at a steep angle? I installed a ruggid ridge steering conversion and I have a pitnan arm drop. It steers fine just a bit touchy for my taste. As far as swaybars go the jks quick disconnects seems like a good option but I belive there work for up to 6" of lift or so. If I go this route I am assuming I'll have to make spacers for the sway bar for it to be able to work with my lift setup?
Could you explain more about the drag link u joint? I imagine you are talking about the rod end. But yes if this is your first Cherokee and you haven't had it for awhile I can see how you think its touchy. Xj's are known for touchy gas pedals and quick steering. You may try a steering stabilizer or double stabilizer to make you feel a little more comfortable, I know that helps a lot of guys. Also as cdn_xj said earlier it looks like you have no track bar, could you post a pick of the front view?
I meant to say ball joint lol I am wondering cause the steering is meant for not over 4 in of lift... Overall it steers fine just not sure if the angles are too extreme.
Thank you for the detailed response regarding all the issues I am dealing with. I do plan on adding a sway bar and sometime in the future I will defiantly go to long arms. Also I am running a RE adjustable trac bar. After I adjusted the caster I did the "redneck" alignment for the time being. I am taking my rig to a alignment shop here in SoCal that specializes in lifted jeeps. I am also running ruggid ridge HD steering with a drop pitman arm. So it will be nice to hear what this specialized alignment shop will have to say about the geometry of everything. I know an over the knuckle kit would be the right way to go with this setup and will possibly upgrade in the future but I am going one step at a time lol
Unless you have a guy already, and if you live in the valley area please I would not recommend this specialty guy on the corner of Woodley and Nordoff. In the past he has done ok work but the problem he has is with his guys that he hires always not doing the work properly and shotty work the rest of the time. Last time I went there he did not even do the work it felt like. I would suggest the 4 wd place on Sepulveda Boulevard. I have only gotten parts there but i hear good stuff over there about them.
06-04-2015, 06:41 PM
Front end caster question
