Slip Yoke

[Luke]

Latest Update : Replaced rear UCA and the vibes did drop ... but only the ones being transmitted to the body through the non existent bushings.

Took it in to have the (original) rear pinion seal replaced, my mechanic took her for a spin and his bet is on the pinion angle. He suggested modification of the existing arms until I told him about the interchange possibility with the TJ/LJ adjustable arms.

I think "the_dealer" actually answered this above but I'd like to get confirmation on the exact arms I should hunt for TJ or LJ and what model year?

Any help is appreciated as always!

 

[tommudd]

Latest Update : Replaced rear UCA and the vibes did drop ... but only the ones being transmitted to the body through the non existent bushings.

Took it in to have the (original) rear pinion seal replaced, my mechanic took her for a spin and his bet is on the pinion angle. He suggested modification of the existing arms until I told him about the interchange possibility with the TJ/LJ adjustable arms.

I think "the_dealer" actually answered this above but I'd like to get confirmation on the exact arms I should hunt for TJ or LJ and what model year?

Any help is appreciated as always!

If you install longer lower rear control arms it is going to make the pinion angle worse. The tech just saw lift and assumed thats what it was I would say. So the TJ/LJ arms are not a fix

 

[CactusJacked]

If you install longer lower rear control arms it is going to make the pinion angle worse.

When the rear of the Liberty gets lifted, the rearend is dropped at an angle because it's hanging off of the lower control arms. Because it's lowering at an angle, simple geometry dictates that the pinion yoke would be raising, throwing off the front to rear pinion angles. If you have a hard time grasping that, pretend you dropped the control arms at a 90 degree angle from where they are now, and imagine where the pinion would then be pointing. This is also why you end up with noticeably less tire to fender clearance in front of the rear tire compared to the back, where you didn't before the lift. So then, why would a longer lower control arm that could slide/rotate the rearend back to where it was, make pinion angle even worse?

 

[tommudd]

No problem at all grasping it,:happy175::happy175::happy175::happy175: I know what I am talking about
Install longer lower control arms and you are pushing the front down more, simple as that. If leaving the stock UCA in place then thats all that happen
No big long explanation needed to sound good

 

[Luke]

Interesting ... he actually suggested shorter not longer. :fishing1:

So the adjustable arms won't get me + and - the stock KJ length?

 

[tommudd]

I have never been able to figure out why some think installing longer lower rear control arms would help with the pinion angle. This has come up at least once a year for the past ten years on one of the forums. You can't change one without changing the other very simple.
When you lift the pinion angle of course changes but not enough to matter in 99% of us. Mines been lifted over 185,000 miles now, and never had an issue with vibrations etc. Only issue with the amount of rear lift I run blowing up the tri-link every so often, part of that is the angle, other is my method of taking off:shrug: .

 

[tommudd]

Interesting ... he actually suggested shorter not longer. :fishing1:

So the adjustable arms won't get me + and - the stock KJ length?

See someone else who actually knows suspensions
Good mechanic, or I assume that is who you are talking about

 

[Luke]

I searched high and low for him ... 3rd generation out of the same shop. Dirty, oil on the floor, old parts up against the wall, a mangy old Sheppard by the back door... and things getting done the right way all over the place He's the only one who could align me at 4".

There was a nice '65 mustang convertible and a perfect black 69 'Cuda in the shop today!

So... I still have the same question(s) :happy175:

 

[tommudd]

My kind of shop
I grew up hanging around and doing what I could in places like that in the 60's

 

[tjkj2002]

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To use longer rear LCA's you'd have to drop the t-case to get even angles.Move one angle you must move the other angle to match.


What I got to deal with....................

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Much easier but time consuming figuring out "cruise throttle".

 

[TwoBobsKJ]

Sorry for just jumping in here...

Shouldn't we be talking about the UPPER control a arm to fix the pinion angle? On a lifted KJ, moving the upper balljoint toward the rear bumper will raise the yoke, correct? Since the LCA's provide the pivot the upper arm is the means to change the angle.

Well...?

Bob

 

[the_dealer]

Correct, BUT...when running a standard 2 joint driveshaft, you want 0-3* of difference between the output shaft angle and pinion angle. When you lift the rear(coil spring), the axle follows the arc of the lower arms. The higher you go, the more of the arc. Here's a picture as an example:

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See how the rear tire is pushed forwards in the wheelwell. At ride height it was perfectly centered. So pretend it's sitting like that at ride height, the pinion actually starts pointing up(to an extent). TJ/LJ lifts come with longer lowers, to restore wheelbase. True, they will change the pinion angle, but not much. If you use the lowers to set the pinion angle, you will actually be making it worse. Lowers set wheelbase, and uppers set the pinion angle.

With that said, I don't even know why JBA has the long arm lowers, but uses a stock length upper. You won't gain anything besides restoring the wheelbase. The stock length uppers will always max out before the lowers, and your axle will move in an unnatural arc. Guys run long arms for less of a pinion angle and wheelbase change throughout the whole arc of travel. The longer the arms, the less angle through their arc of travel, but that only applies if the uppers and lowers are around the same length. Its like going up a 60* hill that's 20ft long, then going up a 60* grade that's 200ft long. The shorter hill will make you crap your pants, but the longer one doesn't seem as steep because of gradual change vs length

 

[Luke]

moving the upper balljoint toward th rear bumper will raise the yoke, correct?

Which would also happen if you shortened the LCA ... No? and seemingly much easier to accomplish. I'm tryin' to grasp it all.

The concept is a shorter LCA not longer. (not directed at you Bob)

Thanks for the input(s) :waytogo: (directed at you Bob... and others) :happy175:

 

[the_dealer]

Yes and no. To an extent It would work, but you are already losing wheelbase due to lifting, why lose more? Moving your wheelbase forward will put your d/s in even more of a bind. Here's my example, my old TJ with 2"ish of rear lift, stock ds, fixed RE lowers, and 3/8" of tc drop.

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Notice how the pinion is still pointed high? Imagine that without the t/C drop and stock length arms. With the extended arms, the pinion and output are within 3*(actually 2.25*). Because of the axle's arc of travel, the pinion was rotated farther up do to the lift, the lowers brought it back down.
Here's the same rear springs, same fixed lowers, no tc drop, but with an SYE and adjustable uca's.

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The uppers are actually adjusted SHORTER than stock by 1/4"(2 turns). The fixed lowers were 1/4" longer than stock, without those, the uppers would have been around 1/2" shorter(but wouldn't have gone that short). My wheelbase would have been off as well. See how they kinda go hand in hand?
My wheel was perfectly centered at ride height.

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Without the lowers, my wheelbase would be off, and I'd never be able to get the uppers adjusted short enough. Every rig is different. I had ome rear coils and needed an sye. Others with the identical setup got by with stock arms and no tc drop or sye.

 

[the_dealer]

Forgot to mention, the pinion and and driveshaft angle needs to be -1.5* to 0 degrees for an sye. Setting it a tad lower help combat vibes due to axle wrap. The output shaft angle doesn't apply due to the dual cardan setup. Now it is possible to run an sye with a standard 2 joint slip style driveshaft shaft (like stock rubicon). An sye will lengthen your driveshaft due to a shorter output shaft (and lack of slip yoke length), which alot of times gets rid of the vibes. In that case you still want to go by the less than 3* of separation rule. It doesn't matter whether the output shaft is at a lesser angle, or the pinion...just as long as there's no more than 3* of difference between the 2. You do however, get to a point to where driveshaft angle comes into play, but that's only with short rear shafts and alot of lift (such as SWB jeeps and Suzuki's). Hope I explained it a little better, it's kinda hard without doing hand motions and gestures lol

 

[Luke]

I hear you on the wheel base .. I only have just over 2" left between the front of the rear tire and the fender flare... not much room to experiment.

I will find another shop to check the balance of the shaft again but not hoping for much.

Beyond that the only way to get rid of my vibes it seems is to un-lift a bit. Which requires taking those damn coil overs out again and taking them to the shop to remove the Frankenlift lower spring perch thing-a-ma-bob! to lower the front at the same time... again! :happy175:

Oh Joy

 

[profdlp]

Luke, your Jeep goes up and down like hemlines on a woman's skirt. What are the fashionable ladies in Paris going to be driving this fall? :happy175:

 

[Luke]

Every rig is different. I had ome rear coils and needed an sye. Others with the identical setup got by with stock arms and no tc drop or sye.

This is a very important concept for anyone who is going to lift their rig to understand ... as I have learned. :whip:

Don't get me wrong, my KJ is the best all around vehicle I have ever owned and everything I want it to be... except vibe free at 70-80 kph :happy175:

 

[Luke]

Luke, your Jeep goes up and down like hemlines on a woman's skirt. What are the fashionable ladies in Paris going to be driving this fall? :happy175:

See that's the problem .. they should (both) always only be going up! :ROFLJest:

 

[CactusJacked]

Because of the axle's arc of travel, the pinion was rotated farther up do to the lift, the lowers brought it back down.

This is exactly what I was saying in my post, and your results supported that. Careful man, you might be accused of "not knowing suspensions" too (people can ROFLMAO all they want, I could give a flying crap)!!
Mainly what I don't like about what the lift does, is how goofy the Liberty looks with the rear tires so far forward in the wheel opening. A lower arm long enough to put the tires back on center would negatively effect pinion angle, without the use of adjustable uppers as well, which, would be a heck of a slick setup to have.