Adjustable Control Arms and Stock Driveshaft

SoCalGlide

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I made a post over in the “What did you do to your LJ today?” about this, but I thought I might get broader coverage here.

Like most of you, I am upgrading my Jeep to be more capable offroad. And like most of you, I don’t have a boatload of cash to throw at it and get it all done at once, so I’ve been doing it in stages as funds allow.

My 2006 LJ has a 4” SL, 1” MML, and a 1” BL. With this combination, I had no vibes with the stock driveshaft. Over the weekend, I installed an Undercover Fab Extra Clearance TC skid, along with their Engine skid. Hoping to buy some time before needing to buy adjustable control arms, I installed the TC skid with a 1-1/2” spacer kit.

This combination ended up raising the output of the TC by ½” over the stock TC. The axle has a 2-1/2° difference from the TC. The front of the axle needs to come down. I am getting vibes in the 50-55mph range. It seems to smooth out at 60 and over.

The gist of all of this is, can I use adjustable control arms to correct the angles with the stock single carden driveshaft?
 
It won't be pretty, but if you can drop that t-case skid by another 1/2 - 5/8", that should put it back where it was and get you vibe-free if you want to put off the adjustable CA's for a while. I recently installed their extra clearance skid and measured that it raised the trans mount by 2-1/8". I have the 1/4" version, so if yours is 3/8" the difference may be smaller. I don't know if they change their designs to account for material thickness.
 
If I were you, I’d get a double cardan rear driveshaft and adjustable control arms.
The SYE and double carden are in the cards, just not right now. Time and money are getting in the way of that.
It won't be pretty, but if you can drop that t-case skid by another 1/2 - 5/8", that should put it back where it was and get you vibe-free if you want to put off the adjustable CA's for a while. I recently installed their extra clearance skid and measured that it raised the trans mount by 2-1/8". I have the 1/4" version, so if yours is 3/8" the difference may be smaller. I don't know if they change their designs to account for material thickness.
I've have ordered Savvy control arms, so I was hoping I could get that 2-1/2 to 3° adjustment with the rear axle without causing other problems, while keeping the stock driveshaft for now. I probably should have done as you suggested and simply lowered the TC skid another 1/2" or so for now. Maybe I'll do that and put the controls arms on the shelf until I get the SYE and double cardan driveshaft.
 
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Depending on how much fiddling around you're up for, you could always install the new upper arms and try to dial in the pinion angle. Take an angle measurement before you pull off the old arms just in case you need to revert back to it. There's a chance you could make the pinion happy and still be ok with the stock driveshaft. As long as the shaft doesn't bind throughout it's entire range of suspension travel, you might just luck out.

If it doesn't work out you can always return the pinion angle to what it was and lower the transfer case further. At that point you've given yourself some good practice for the future mods you have coming.
 
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The SYE and double carden are in the cards, just not right now. Time and money are getting in the way of that.

I've have ordered Savvy control arms, so I was hoping I could get that 2-1/2 to 3° adjustment with the rear axle without causing other problems, while keeping the stock driveshaft for now. I probably should have done as you suggested and simply lowered the TC skid another 1/2" or so for now. Maybe I'll do that and put the controls arms on the shelf until I get the SYE and double cardan driveshaft.

If you have them, might as well put them on.

I've never pushed an LJ to see what it would tolerate, but with my TJ I found the limit of operating angle where no matter how perfect my pinion angle was, I just couldn't get the vibes out. With 3" of lift and a motor mount lift, I still needed about 5/8" of t-case drop, and it rose to about 1-1/4" when I regeared from 3.73 to 4.56 because the max operating angle decreases with increasing driveshaft rpm. You may get lucky, if your gears are still stock, and be able to find a pinion angle that smooths it out.
 
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If you have them, might as well put them on.

I've never pushed an LJ to see what it would tolerate, but with my TJ I found the limit of operating angle where no matter how perfect my pinion angle was, I just couldn't get the vibes out. With 3" of lift and a motor mount lift, I still needed about 5/8" of t-case drop, and it rose to about 1-1/4" when I regeared from 3.73 to 4.56 because the max operating angle decreases with increasing driveshaft rpm. You may get lucky, if your gears are still stock, and be able to find a pinion angle that smooths it out.
Like you and @SvtLdr suggest, I'll install the control arms and fiddle with it. I'll get my answer that way, good or bad.
 
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Some Jeep porn showed up yesterday. I did get the complete Savvy control arm set, these are just the rear arms.

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I made a post over in the “What did you do to your LJ today?” about this, but I thought I might get broader coverage here.

Like most of you, I am upgrading my Jeep to be more capable offroad. And like most of you, I don’t have a boatload of cash to throw at it and get it all done at once, so I’ve been doing it in stages as funds allow.

My 2006 LJ has a 4” SL, 1” MML, and a 1” BL. With this combination, I had no vibes with the stock driveshaft. Over the weekend, I installed an Undercover Fab Extra Clearance TC skid, along with their Engine skid. Hoping to buy some time before needing to buy adjustable control arms, I installed the TC skid with a 1-1/2” spacer kit.

This combination ended up raising the output of the TC by ½” over the stock TC. The axle has a 2-1/2° difference from the TC. The front of the axle needs to come down. I am getting vibes in the 50-55mph range. It seems to smooth out at 60 and over.

The gist of all of this is, can I use adjustable control arms to correct the angles with the stock single carden driveshaft?
No, you need a DC if your going to adjust your pinion
 
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Why? It's my understanding, with a single cardan driveshaft, that the output shaft of the TC and the input shaft of the axle need to be parallel. If I can get that through adjustable control arms, without u-joints binding, why wouldn't it work?
You’re right in principle, but that only works till the angles are too steep at the yokes. You are acknowledging this with the TCase drop. Drop it further.
 
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When the angles get too high you have wear problems, you don't have vibes, I don't know what @JMT is really talking about.
Please correct me if I’m wrong. I’m just saying that if the pinion and TCase out are parallel, but 1 is 10 feet higher than the other, a SC shaft isn’t going to work (hyperbole only to illustrate there’s a limit in how high you can raise the TCase above the pinion before the angles are just too much). Correct me if I’m crazy. He wants to get CA’s to adjust the pinion down I think, to get them parallel.
 
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Correct me if I’m crazy.
If they are close to parallel on an LJ it will probably work fine. They will wear faster than a DC but they shouldn't cause vibes. 10 feet will cause bind, of course that is bad but my opinion is this isn't at that level of crazy. High angles just cause excessive wear on standard shafts, DC cuts the angle each joint works in half, that's really why they are used.
 
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i think he's suggesting if the joints good for 28* and your using 25* sitting in the driveway whats left for your down travel?
 
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i think he's suggesting if the joints good for 28* and you using 25* sitting in the driveway whats left for your down travel?
There is a massive difference between angles that are okay for general use/wear and bind. I'm pretty sure this is a short term thing until there are funds to do the DC but I could be wrong.
 
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A lot of good points here, and I am not going to discount any of them, and tells me what I need to look for. I will check for u-joint bind at full droop.
I'm still learning, even at my age. I think fortunately, with an LJ, the driveshaft angles aren't too severe. I'm hopeful I will be able to get away with this short term. Yes, a SYE and double cardan driveshaft are in my near future.
 
Throughout the different phases of my build, I have done different things to try and get rid of vibes. I have a TJ, not an LJ. Right now, I'm running a motor mount lift, UCF extra clearance skid, and a TW rear DC driveshaft. I have 4" of spring lift. I have Currie adjustable control arms. I am Vib free.

When I was at 2" of spring lift, factory control arms, and 33's, I actually raised the T-case a bit off the skid, after I did the MML. I was getting a faint, pulsing vibration around 55-60, so I put 3/4" of spacers in under the Transmission mount and that made the difference. That was with the factory skid and a factory DS. Not sure why mine was "weird" but it was.

So...can you get rid of your vibs using a single cardon driveshaft? Maybe. Its definitely worth playing around with. Make sure you go to full droop with the axle and check for binding. You already bought the control arms so, if it works, you save yourself 350 bucks not needing to buy a DS. If it doesn't work, you'd need the control arms anyway, and you just need to pony up for the DS...and maybe a SYE. Not sure if you have a Rubi or not. I do, so I didn't need to worry about an SYE kit or anything.
 
No, not a Rubi. :cry: But, your point is what I was thinking. If I end up needing a DC driveshaft, I would need the adjustable control arms anyways. If the control arms work, that'll be great.
 
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Okay, yesterday I got the rear control arms installed and adjusted. I spent more time cycling and adjusting than the actual install.

Did it work? I'm going to give it a qualified yes. I got rid of the vibration, but as @JMT suggested, the driveshaft angles may be a bit too much for this to be a permanent solution. As @pagrey said, I'm going to trade off some accelerated wear for smoothness.
Ultimately, the SYE and the double cardan driveshaft are the solution. But, I think I can easily buy myself a month or 2 until then.
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