Adjustable Front Upper Control Arms

I understand the need for adjustable rear upper control arms for a
lift with a SYE and CV shaft. What reason would someone use
adjustable front upper control arms?

Scotty

On Sun, 08 Jul 2007 16:18:22 -0700, Scotty >
wrote:

> What reason would someone use
>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 , SnoMan at
wrote on 7/8/07 7:54 PM:

> On Sun, 08 Jul 2007 16:18:22 -0700, Scotty >
> wrote:
>
>> What reason would someone use
>> adjustable front upper control arms?
>
>
> Adjust axle Caster.
> -----------------
> TheSnoMan.com

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 - Gone to the rust pile...
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)


Scotty wrote:
> I understand the need for adjustable rear upper control arms for a
> lift with a SYE and CV shaft. What reason would someone use
> adjustable front upper control arms?
>
> Scotty
>

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.

"Mike Romain" > wrote in message
ng.com...
> 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 - Gone to the rust pile...
> Canadian Off Road Trips Photos: Non members can still view!
> Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
> (More Off Road album links at bottom of the view page)
>
>
> Scotty wrote:
>> I understand the need for adjustable rear upper control arms for a
>> lift with a SYE and CV shaft. What reason would someone use
>> adjustable front upper control arms?
>>
>> Scotty
>>

On Tue, 10 Jul 2007 18:15:56 -0400, "Matt Macchiarolo"
> wrote:

>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.


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.

<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, >

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

<most of the center feel is
from steering box not caster>

<but caster will effect how it follow or
track road when centered. >

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

"Matt Macchiarolo" > wrote in message
...
> 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.
>
> "Mike Romain" > wrote in message
> ng.com...
>> 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 - Gone to the rust pile...
>> Canadian Off Road Trips Photos: Non members can still view!
>> Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
>> (More Off Road album links at bottom of the view page)
>>
>>
>> Scotty wrote:
>>> I understand the need for adjustable rear upper control arms for a
>>> lift with a SYE and CV shaft. What reason would someone use
>>> adjustable front upper control arms?
>>>
>>> Scotty
>>>
>
>

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 a
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 , SnoMan at
wrote on 7/10/07 9:54 PM:

> On Tue, 10 Jul 2007 18:15:56 -0400, "Matt Macchiarolo"
> > wrote:
>
>> 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.
>
>
> 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

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

>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 a
>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

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