Adjustable Front Upper Control Arms

Adjust axle Caster.

----------------- TheSnoMan.com

I would have to go with snoman adjust axle caster

99 wrangler 5 speed stick 2.5 inch lift 31 inch MTR tires

You can adjust the caster AND keep the axle centered the the wheel wells (front to rear). However, I would say that they are an expensive addition, and you probably won't get the most value for the money. Caster can be adjusted with adjustable lower control arms.

Paul

in article snipped-for-privacy@4ax.com, SnoMan at snipped-for-privacy@snoman.com wrote on 7/8/07 7:54 PM:

To keep the front end alignment within specs. When you lift, the pumpkin tilts which throws off the alignment bad. Same for the rear, you need to keep the driveshaft u-joints aligned also.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's - G> I understand the need for adjustable rear upper control arms for a

The primary reason for caster adjustment is to have proper driveline angles. Caster doesn't have an affect on alignment like a drag link or tie rod, but caster changes will affect the "on-center" feel of the steering wheel.

According to the FSM, proper driveshaft angles are priority over on-center feel of the steering wheel.

Caster plays a BIG roll in how vehcile tracks and responds to road forces and whether or not it is prone to death wooble. It is not just for steering wheel return to center. BTW, most of the center feel is from steering box not caster but caster will effect how it follow or track road when centered.

----------------- TheSnoMan.com

Yes but in a solid axle vehicle caster is less critical than say in an IFS. Death wobble is due to a combination of caster, worn linkages and poor toe-in.

Nevertheless, page 3-15 of my FSM: "Having the correct pinion angle does have priority over having the preferred caster angle."

In other words, caster effects the on-center feel. Didn't I already say that?

The front driveshaft on my Rubicon is a CV shaft, with the double cardan joint just in front of the t-case. Isn't that the same for all TJs?

The manual says the driveline angles are more important than the caster, but the specs appear to be for a single cardan front drive shaft instead of a double cardan. The specs are: Within 1 degree u-joint cancellation Operating angles less than 3 degrees At least half a degree operating angle.

Your t-case factory mount should give you 3 degrees down from horizontal. Factory front pinion angle is 3.2 degrees up from horizontal. This gives a u-joint cancellation of .2 degrees. The t-case output yoke operating angle is 1.9 degrees and the pinion input yoke operating angle is 1.7 degrees.

You can increase the operating angle by about one degree at the t-case yoke. Any mathematicians know how much lift that is? I don't know the length of the front drive shaft, but I'd have to say not much. That's why you see a lot of t-case lowering kits.

If the driveline angle is greater that three degrees, you will get a steady vibe in the pinion shaft which will eventually wear out the pinion bearing. If you have a single cardan joint in the drive shaft, you will get a similar vibe in the t-case output yoke. The vibe will be twice the rotational speed of the drive shaft because the pinion will actually speed up and slow down twice per revolution. At 2000 RPM, the vibe is like a hum (close to 60Hz), so it isn't that noticeable. At slower speeds, there is less force on the u-joint, and also hard to notice the vibe. You won't see the damage coming!

If you have a double cardan joint in your front drive shaft, I think the specs in the repair manual are less critical. On my rubicon, the double cardan is up near the t-case yoke, so the critical angles will be down near the pinion. You want a small operating angle, probably half a degree. If the operating angle is zero, the u-joint at the pinion will not stay lubricated and may freeze up due to no rotation in the bearing caps. However, the operating angle at the double cardan can be larger than 3 degrees. This means you probably don't need a t-case lowering kit, but you might need to increase your pinion angle to more than the factory 3.2 degrees. to keep the operating angle small.

Paul

in article snipped-for-privacy@4ax.com, SnoMan at snipped-for-privacy@snoman.com wrote on 7/10/07 9:54 PM:

On Wed, 11 Jul 2007 07:22:53 -0500, Paul Nelson wrote:

Nice observations. While Ujoint angle is important, front axle caster angle does not need to be compromised to do it. If you are into serious lifts you have two options, the first is to use CV's on both ends of drive shafts which helps a lot with jeeps short drive shafts and the second is for real hard core lifts. With this one you cut axle tube weld loose for differentail casting and rotate diff housi up to correct drive angle problem whil keeping caster properly set. You are alos correct that about 3 degrees is about all you really want to run u-joint at under high speeds and heavy load if you want smooth operation and long joint life. One more thing, when setting pinion drive angle, remember that rear diff torque upward in spring when forward drive is applied to rear axle so you actually want to set it to take this in to consideration. Depending on spring, tire and input power combo the yoke can torque up 5 to 10 degrees at times so ti is waise to set it maybe 3 to 4 degrees pinion down so that angle is near nuetral under load. If you set it nuetral static it will be pinion up under load. On front axle, it is the oposite, the pinion yoke torques down under forward motion torque input and this is why it can get ugly up there with lifts because pinion tries to tip down more under load with big tires and if you tip it up more to try to fix this you can throw caster out the window and this is why CV joints should be used with Jeep lifts of more than a few inches unless axle is reindexed as above.

----------------- TheSnoMan.com

I am no so sure that I share this view. Solid axles as not immune to this and in someways even more sensitive to it it you want it to track correctly. My 89 4x4 burb will track for a long time hands off on a good highway road before requiring correction even after 180K plus miles. When it was new I added caster shims between spring pads and springs to add about 2 degrees of positve caster to it or stock setting as I recall because I did not like the way it tracked when new and those shims are still in there today.

----------------- TheSnoMan.com

I think caster is important in any vehicle, no matter what front end it's got. Caster helps, just like you say, essentially keeping the wheel centered at high speeds. I would consider it a safety item even. Incorrect caster can lead to an unstable vehicle on the highway.

If someone is going through the work to lift their vehicle enough to turn the pinion up on the front end to the point of 0 caster or negative caster, they should seriously consider having the axle either cut & turned so that both pinion angle & caster are correct, or get a new axle that's got the proper angles for your lift built in.

It might not be so much of an issue with ifs simply because the caster can be set independantly of the pinion angle...

Clay

Yep, but pinion angle is measured at the pinion.

I would surmise these are the specs for the rear driveshaft.

The T case lowering kits are primarily to correct the rear driveshaft angles, not front driveline angles.

You will probably see adequate rotation of the bearing caps from normal cycling of the suspension during road operation.

True, but the pinion angle at the axle is what we're talking about.

I agree, I never said it wasn't important, I said things like toe-in and draglink settings are more critical. To clarify, that would be on a moderately lifted Jeep like mine, where the caster was affected by the pinion angle ajdjustment , yet it does track well on the highway.

Caster helps, just like you say, essentially keeping the

Agreed, but a typical 4-5" lift wouldn't set the caster so far out of spec as to make the handling unsafe.

Caster is important period. If you are runnignnwith nuetral to negative caster you are playing with fire on a lifted 4x4 beacuase it raises possible of control loss due to front end oscillation when conditions are right.

I would not say that at all either (I guess you hae never actually aligned many or any 4x4 front ends) . Actually a lift with big tires and increase tread contact and rolling resistance increases the need for more postive caster. Caster needs to be changed with lift and tire size and if you want to get really techical, camber should to (one of cambers functions to to center bearing load properly on spindle) Sure some squeak by but then some get the crap scared out of them when they get a bad case of the death wooble at the wrong time. (I have seen them shake so bad that they can take a 4x4 right off the road, especailly a short wheel base Jeep)

----------------- TheSnoMan.com