UCA axle end bushing options?

[RCP Phx]

The RC long arm mounting point on the unibody rail is about 1/2 - 3/4" further inboard than the stock lower control arm mounting point. Now that you mention this, I suppose that moving the mount point further inboard produces some triangulation, but its not obvious to me how that affects flex requirements. I really need to manually flex the suspension or simulate it.

I moved my arms in about 2-1/2" further in and about 3/4" up. This is a pic of my first set crossmember from 2003, and I made small improvements on 2 more later.

 

[maxbraketorque]

Stick both of your arms straight out with your top fingers in a "v" and move one up and arm down and you will see the torsional problem.

The Johnny joints that attach the long arm to the unibody will take care of necessary rotation of the long arm as the axle is tilted. But are there any other flex needs?

 

[RCP Phx]

Only all the axle and CA bushings, I did finally kill a set after 15yrs and the Rubicon, Moab, Ouray and our local hard core trails!

 

[RCP Phx]

I should add that those were rubber bushings, if you put any kind of a "hard" joint in there you will tear off the upper pass side mount off the axle.

 

[gearwhine]

The Johnny joints that attach the long arm to the unibody will take care of necessary rotation of the long arm as the axle is tilted. But are there any other flex needs?

It seems like there is still not total clarity of the bind being spoken about in this thread and why bushing selection is being discussed.

The spoken about bind in this thread has to do with, basically, pinion angle, and not specifically the rotation/flex of the axle when looking at it from the front or back of the Jeep.

When the whole axle compresses....say on a speed bump, the pinion of the axle will generally begin to angle downward to continue to point to the T-case. When at full droop of both wheels, that pinion angle will turn slightly upward toward the T-case. No bind in either of those case....but when one wheel is up, and one is down....that's when things get funky.

Now there is a battle over pinion angle between the two sets of control arms. In order to maintain a single pinon angle, a control arm needs to be shortened or lengthened somewhere to allow for it. This is why rubber bushings are recommended somewhere in a 4 link w/ trackbar or on a radius arm setup....they allow for that slight lengthening and/or shortening. Removing an upper link to go to only 3 attachments at the axle removes this issue entirely.

I am cranky because my new UCA clevite bushings have failed in about 1k miles on a 3" lifted XJ. My old XJ had clevites going for thousands of miles with a 6" lift and way more offroad miles with more flex. I want to get rid of them entirely now, but don't want to break anything by doing so. I still wager that the pinion angle doesn't change much with less than extreme flex, evidence being the many jeeps running Johnny Joints at all points of contact on stock style suspensions. The issue is always present, it's just a matter of degree of severity. A severity that I don't know at this time without going out and measuring.

Ok...too much. No more for me today.

 

[RCP Phx]

My pinion always stays pointing at the TC because the LCA is parallel to the driveshaft.

 

[maxbraketorque]

It seems like there is still not total clarity of the bind being spoken about in this thread and why bushing selection is being discussed.

The spoken about bind in this thread has to do with, basically, pinion angle, and not specifically the rotation/flex of the axle when looking at it from the front or back of the Jeep.

When the whole axle compresses....say on a speed bump, the pinion of the axle will generally begin to angle downward to continue to point to the T-case. When at full droop of both wheels, that pinion angle will turn slightly upward toward the T-case. No bind in either of those case....but when one wheel is up, and one is down....that's when things get funky.

Now there is a battle over pinion angle between the two sets of control arms. In order to maintain a single pinon angle, a control arm needs to be shortened or lengthened somewhere to allow for it. This is why rubber bushings are recommended somewhere in a 4 link w/ trackbar or on a radius arm setup....they allow for that slight lengthening and/or shortening. Removing an upper link to go to only 3 attachments at the axle removes this issue entirely.

I am cranky because my new UCA clevite bushings have failed in about 1k miles on a 3" lifted XJ. My old XJ had clevites going for thousands of miles with a 6" lift and way more offroad miles with more flex. I want to get rid of them entirely now, but don't want to break anything by doing so. I still wager that the pinion angle doesn't change much with less than extreme flex, evidence being the many jeeps running Johnny Joints at all points of contact on stock style suspensions. The issue is always present, it's just a matter of degree of severity. A severity that I don't know at this time without going out and measuring.

Ok...too much. No more for me today.

Makes sense for a 4-link suspension, but its not obvious to me that a radius arm suspension has the same issue.

 

[RCP Phx]

That's why I originally my built radius arms, I was getting u-joint/yoke binding at my final height with my RE super-flex kit when it dropped out fully!

 

[gearwhine]

Makes sense for a 4-link suspension, but its not obvious to me that a radius arm suspension has the same issue.

Fair enough, but the the premise doesn't change at all b/w a 4-link or a radius arm set-up. If your pinion angle changes at all through it's travel...the issue is present (barring triangulated 4-links...I'm unsure on those at the moment. Apparently they react differently)

With a radius set-up, the pinion angle ideally continues to point at one place (in relation to where your radius arms are attached at the frame). This doesn't mean the angle isn't changing; it's changing with every slight movement. That angle would be different from pass side to drive side when flexed, so the battle between each side wanting two different angles is still there.

u-joint bind is a totally different issue.

 

[VAhasnoWAVES]

Fair enough, but the the premise doesn't change at all b/w a 4-link or a radius arm set-up. If your pinion angle changes at all through it's travel...the issue is present (barring triangulated 4-links...I'm unsure on those at the moment. Apparently they react differently)

With a radius set-up, the pinion angle ideally continues to point at one place (in relation to where your radius arms are attached at the frame). This doesn't mean the angle isn't changing; it's changing with every slight movement. That angle would be different from pass side to drive side when flexed, so the battle between each side wanting two different angles is still there.

u-joint bind is a totally different issue.

correct, they work in a similar fashion. as the axle goes through its range of motion staying level, the arms arent fighting each other. but once articulated, one side is trying to drive the pinion down while the other is trying to push it up. the amplitude of this is based on geometry. but its a balancing act and not all about pinion angle.

controlling the pinion explicitly is fin for a rock crawler, but what about a go fast rig? or even a rig that sees a lot of highway speeds? those may put a bigger priority on castor through the range of motion.

 

[maxbraketorque]

I guess this answers my question as to the amount of misalignment that can occur. Impressively large amount, but they don't say how much the suspension was flexed to get this much misalignment.

https://www.youtube.com/watch?v=rzcudE2U6BM

 

[gearwhine]

Impressively large amount, but they don't say how much the suspension was flexed to get this much misalignment.

Yep....that's the exactly detail I'm looking for! That can help dictate what bushing/flex joints are actually appropriate. Metalcloak has been known to make some pretty...say "impressive claims"...about their products. I bet this is pretty extreme flex they're displaying to help sell this product.

 

[maxbraketorque]

I'm going to do the same thing to my suspension this weekend.

 

[RCP Phx]

The Metal Cloak will work but way to expensive considering we've been doing wristed for 50yrs for almost zero dollars!

 

[maxbraketorque]

I should have clarified - I'm going to disconnect the passenger side short arm and obverse the amount of misalignment as I move the wheels through the travel.

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[maxbraketorque]

For about 13 inches of flex, I'm seeing 3/8-7/16 inch of misalignment in one direction. Not trivial. Each of the four axle bushings has to move about 1/8 inch to accommodate this. Not too bad if dealing with only 13 inch of flex. But not sure that relying on bushings makes sense for greater amounts of flex.

And I found that my passenger side UCA bushing is floating free in the housing. It won't pop out by hand, but it freely rattles and rotates.

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[maxbraketorque]

The relationship between amount of flex at the front axle and misalignment should be linear and will be dependent on radius arm length. For my RC long arm suspension that has an arm length of ~30 inches, there will be ~0.034" of misalignment per inch of front axle flex.

 

[RCP Phx]

And I found that my passenger side UCA bushing is floating free in the housing. It won't pop out by hand, but it freely rattles and rotates.

That's typical and easily fixed!

 

[maxbraketorque]

That's typical and easily fixed!

Whack it with a hammer?

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[RCP Phx]

You weld in a full bushing cradle.