Adjustable control arm help

[Reef]

Just recently finished 3” ome/rs5000 lift. Wound up having to do a MML and temporarily did a washer tranny drop as the MML wasn’t enough. The vibes are pretty much gone now but I want to take the tranny drop out and put in a pair of adjustable control arms. I am also wanting a pair for the front as the Jeep wanders badly and the way it feels to me is that it’s a caster issue.
I know that I should change out all 8 of the CA but financially that isn’t happening right now. My question is should I buy uppers or lowers for now to fix rear pinion angle and front caster or does it not really matter.

 

[Jerry Bransford]

Unless you also install a SYE kit and DC (aka CV) driveshaft the adjustable arms will do absolutely nothing to eliminate or even reduce your drivetrain vibrations.

Due to the single cardan rear driveshaft the factory installed your rear pinion angle must remain parallel to the transfer case driveshaft as it is now.

Your drivetrain vibrations are not caused by the rear pinion angle, they are caused by the excessive angles the driveshaft u-joints are working into caused by the height of the suspension lift.

It's likely the vibrations can be stopped by installing a pair of 1" tall motor mount lifts which reduce the angles the driveshaft u-joints have to work into the same way a transfer case drop works. This would be the least expensive alternative to installing a SYE, DC driveshaft, and adjustable length control arms.

 

[Reef]

Unless you also install a SYE kit and DC (aka CV) driveshaft the adjustable arms will do absolutely nothing to eliminate or even reduce your drivetrain vibrations.

Due to the single cardan rear driveshaft the factory installed your rear pinion angle must remain parallel to the transfer case driveshaft as it is now.

Your drivetrain vibrations are not caused by the rear pinion angle, they are caused by the excessive angles the driveshaft u-joints are working into caused by the height of the suspension lift.

It's likely the vibrations can be stopped by installing a pair of 1" tall motor mount lifts which reduce the angles the driveshaft u-joints have to work into the same way a transfer case drop works. This would be the least expensive alternative to installing a SYE, DC driveshaft, and adjustable length control arms.

Is using adjustable control arms to rotate the nose of the diff down not the same outcome as using a MML/ drop to change the angle of the back of the trans?

 

[LONGJP2]

Is using adjustable control arms to rotate the nose of the diff down not the same outcome as using a MML/ drop to change the angle of the back of the trans?

Both can be used to obtain the desired angles.
So yes, you could use adj.arms to lower the pinion.
However, one way decreases the working angle, and the other way increases the working angle.

 

[jjvw]

Is using adjustable control arms to rotate the nose of the diff down not the same outcome as using a MML/ drop to change the angle of the back of the trans?

Vaguely yes, but not really.

 

[LONGJP2]

Is using adjustable control arms to rotate the nose of the diff down not the same outcome as using a MML/ drop to change the angle of the back of the trans?

After rereading your question, I don't think I answered it.
Adding a motor mount lift actually pivots the rear of the trans down (decreasing the angle).
Removing the trans.drop (washers) pushes the rear back up (increasing the angle).

Have you measured either angle to see what the difference is between you trans.output and rear pinion?

 

[Reef]

After rereading your question, I don't think I answered it.
Adding a motor mount lift actually pivots the rear of the trans down (decreasing the angle).
Removing the trans.drop (washers) pushes the rear back up (increasing the angle).

Have you measured either angle to see what the difference is between you trans.output and rear pinion?

I did try to measure the angles using my iPhone but can’t find a good surface to measure from. Where do guys usually measure at? With the 1” MML and a 1/2” tranny drop I have the vibration basically gone so I want to remove the tranny drop and use the adjustable rear arms to lower the pinion angle enough to get the vibration to disappear again. And in the front I need more caster.

 

[Jerry Bransford]

Is using adjustable control arms to rotate the nose of the diff down not the same outcome as using a MML/ drop to change the angle of the back of the trans?

No, that would make the excessive u-joint angle problem causing the vibrations worse.

 

[Reef]

I was under the impression that the biggest factor was that the trans output and pinion angles were kept parallel.

 

[Woodrow]

To your original question: adjustable UPPER control arms are what you should use to set your pinion angle. But, I think an SYE kit (w/ DC rear shaft) and adjustable REAR uppers are what you need to lose the T-case drop. If your vibes are gone, run your drop until your ready to do that. Adjustable FRONT uppers will allow you set caster. You can skip the front and rear lowers for now as long as your stock lowers are in OK shape.

 

[Reef]

To your original question: adjustable UPPER control arms are what you should use to set your pinion angle. But, I think an SYE kit (w/ DC rear shaft) and adjustable REAR uppers are what you need to lose the T-case drop. If your vibes are gone, run your drop until your ready to do that. Adjustable FRONT uppers will allow you set caster. You can skip the front and rear lowers for now as long as your stock lowers are in OK shape.

Exactly the info I was needing. Thanks.

 

[jjvw]

To your original question: adjustable UPPER control arms are what you should use to set your pinion angle. But, I think an SYE kit (w/ DC rear shaft) and adjustable REAR uppers are what you need to lose the T-case drop. If your vibes are gone, run your drop until your ready to do that. Adjustable FRONT uppers will allow you set caster. You can skip the front and rear lowers for now as long as your stock lowers are in OK shape.

Not correct.

Both upper and lower arms together are used to set the pinion and the wheelbase. You cannot adjust one without affecting the other.

 

[jjvw]

Exactly the info I was needing. Thanks.

You got the wrong info.

 

[jjvw]

I was under the impression that the biggest factor was that the trans output and pinion angles were kept parallel.

On a stock single cardan rear driveshaft that is correct. However, a single cardan driveshaft has less available misalignment than a double cardan driveshaft. A double cardan driveshaft requires the pinion to be pointed at the tcase output. Specifically slightly low for the rear to account for axle wrap at higher speeds.

 

[mrblaine]

To your original question: adjustable UPPER control arms are what you should use to set your pinion angle. But, I think an SYE kit (w/ DC rear shaft) and adjustable REAR uppers are what you need to lose the T-case drop. If your vibes are gone, run your drop until your ready to do that. Adjustable FRONT uppers will allow you set caster. You can skip the front and rear lowers for now as long as your stock lowers are in OK shape.

It is not possible to adjust either set of arms, upper or lower without changing both pinion angle and wheelbase. Whether or not there is enough adjustment and enough room for the axles to move around is a different story, but adjusting only the upper or the lower will in fact change both pinion angle and wheelbase.

 

[Woodrow]

Not correct.

Both upper and lower arms together are used to set the pinion and the wheelbase. You cannot adjust one without affecting the other.

Agree. The uppers and lowers do effect both pinion angle and wheelbase but not equally. In the case of both axles on a shock TJ, the uppers attach farther from the axle shaft axis. I assume this is this reason many will choose adjustable uppers if budget doesn’t allow uppers and lowers when they need to fix pinion angle or caster issues.

 

[jjvw]

Agree. The uppers and lowers do effect both pinion angle and wheelbase but not equally. In the case of both axles on a shock TJ, the uppers attach farther from the axle shaft axis. I assume this is this reason many will choose adjustable uppers if budget doesn’t allow uppers and lowers when they need to fix pinion angle or caster issues.

That's nothing more than cutting corners. One cannot change without affecting the other no matter how one tries to justify the contrary.

 

[mrblaine]

Agree. The uppers and lowers do effect both pinion angle and wheelbase but not equally. In the case of both axles on a shock TJ, the uppers attach farther from the axle shaft axis. I assume this is this reason many will choose adjustable uppers if budget doesn’t allow uppers and lowers when they need to fix pinion angle or caster issues.

The reason folks pick uppers is some fucking moron started the fallacy that uppers are for pinion adjustment and lowers are for wheelbase many moons ago and we have yet to collectively get any damn smarter than that.

 

[Woodrow]

The reason folks pick uppers is some fucking moron started the fallacy that uppers are for pinion adjustment and lowers are for wheelbase many moons ago and we have yet to collectively get any damn smarter than that.

So, if your budget constrained you to one or the other, would you choose lower adjustable arms and why?

 

[jjvw]

So, if your budget constrained you to one or the other, would you choose lower adjustable arms and why?

What do the lowers adjust? Pinion or wheelbase or both?