Ideas to solve vibrations?

[jrockrat]

So I did the "Codamans budget lift" without the body lift.
2" ProComp springs on the front and 2" OME spring on the back. Stock control arms all the way around.
At the same time I went ahead and did a 1" motor mount lift (RC aluminum blocks under new stock motor mounts) as a pre-emptive driveline angle solution.
I also went from 30" to running 31" KO2s.
I just got back from my first drive and I've got crazy vibrations that weren't there before. It super noticeable when the drive line is under torque (accelerating).
Did I make a mistake with the motor mount lift possibly and made the drive line worse?
I know some people don't have to do any adjustments when they do that lift.
I also see where a TC drop is sometimes a solution. I thought the motor mount would be the way to go rather than drop the TC to keep a little more height.
Would I need to do both?

Just trying to find some direction as far as a good course of action to try and find a solution. I have a vacation coming up shortly and the Jeep was going to be the vehicle we planned on taking.
Thanks in advance for any help.

 

[MillenniumFalcon]

I suggest trying the tc drop. It's pretty quick and easy as long as you buy a kit or get longer bolts.
We did a RC 2.5" lift on our 99 TJ and had a vibration. Dropped TC and has been fine since.

 

[Woodrow]

I suggest trying the tc drop. It's pretty quick and easy as long as you buy a kit or get longer bolts.
We did a RC 2.5" lift on our 99 TJ and had a vibration. Dropped TC and has been fine since.

I agree. That’s the quickest, easiest solution. An angle finder will be helpful. Assuming a non-double cardan driveshaft (just one u-joint at either end, which a stock Wrangler X should have), then you want your pinion and T-case output shaft angles within a degree or so (usually the T-case shaft slightly steeper than the pinion). Washers and longer T-case skid bolts will be needed. The stock bolts are conical but regular or flanged grade 8 bolts with washers will probably work in a pinch. Ultimately, you might need a DC driveshaft but many don’t with 2” of lift (and I’m a little surprised you have a big vibe with a 2” spring lift + MML). My TJ had a bad vibe when I bought it with a 3” spring lift and a 1.5” T-case drop. I fixed it with a slip yoke eliminator kit for the transfer case and adjustable rear upper control arms to rotate my pinion up and was able to ditch the T-case drop. I also had to extend my axle side rear shock mounts rearward to keep the shock body from contacting the axle tube with the newly rotated axle position. Overall, this is a good example of many mods opening a big can of worms

 

[pagrey]

There is a small possibility your front driveshaft is causing the vibes, very small. That's the only way I can see a MML causing you issues. You might pull the front shaft and test. Measuring the angles is smart too. Sometimes 2" lift is really three and that doesn't work so you might be stuck with a SYE and arms.

 

[freedom_in_4low]

The fact that you said it happened on acceleration and didn't mention a speed if onset implies to me that it's not a total operating angle issue but a mismatched angle issue. Get an angle finder and take some measurements before you do anything. With only 2" of lift a MML may have overshot on the driveline angle and your pinion may be too low, and a TC drop might make it worse instead of better. I've seen it happen.

 

[jrockrat]

There is no speed that it comes or goes at. I can feel it from the moment I start to accelerate and it continues no matter what speed.
I'll see if I can come up with something to measure the angles.
A lesson here for me is only make one change at a time, that way it would be easier to find out what brought on the problem.
I'll let you know what I find.
Thanks

 

[someguysjeep]

some pics of that rear driveline angle might help.

 

[jrockrat]

If I did this correctly it looks like there is about 4 degrees difference. From my understanding there needs to be 0 difference for a stock rear drive shaft.
Using a bubble level on my phone I get about 3.5 degree difference, -9.6 at the rear and -6.1 at the TC.

 

[someguysjeep]

for the stock shaft you want those to be the same angles. your rear pinion angle is fixed, but you can drop belly skid to get you back close.

put a jack under the skid and loosen the bolts so it starts to drop and see if you can reach 79-80* at the TC output.
if you have enough bolt engagement left you can stuff it with washers and be fine, go see if that fixes ya.. if you don't have enough engagement, it'll require longer bolts. and maybe something better than stacked washers.

 

[NashvilleTJ]

for the stock shaft you want those to be the same angles. your rear pinion angle is fixed, but you can drop belly skid to get you back close.

put a jack under the skid and loosen the bolts so it starts to drop and see if you can reach 79-80* at the TC output.
if you have enough bolt engagement left you can stuff it with washers and be fine, go see if that fixes ya.. if you don't have enough engagement, it'll require longer bolts. and maybe something better than stacked washers.

This ^. And to clarify for the OP, the 0 degree setup you have read about applies only to a double cardan driveshaft.

 

[someguysjeep]

the MML was not a wasted effort it saved you from having to drop the TC skid 2x as much.

 

[jrockrat]

Well, I tried dropping the TC over an inch and still was almost 2 degrees off. I'm really baffled that it's that far off with this small lift. That's why I went with the 2" lift because the consensus was that it wouldn't require anything crazy. I'm at the point that I think I'm going to go back to the stock springs until I can afford the SYE and adjustable arms. Guess I'm one of the rare cases that it's not as easy as it looked.
Thanks for all the suggestions.

 

[HardSell]

"it's not as easy as it looked. "

It never is.

 

[Shawn at Tom Wood's]

Here is a page we put together showing how to diagnose drive shaft vibrations. https://4xshaft.com/blogs/faq/diagnosing-drive-shaft-vibrations?_pos=1&_sid=d6ec76a03&_ss=r

Yours does sound angle related which probably means an SYE and double cardan drive shaft are in order. However you do have a relatively small lift and the other things you've done should mitigate some of the angle changes. So I'm not 100% sure it's drive line angle that's causing the problem, could be something else entirely. I don't see if you've posted it or not but I don't know what the angle of the drive shaft is, that's an important part of the equation, how it relates to the angles of the t-case and pinion.

This video might be helpful, and/or the one on our youtube channel titled What is a Slip Yoke Eliminator.

 

[jrockrat]

Thanks for that info. Here's some new pics and angles
Measuring off the back of the diff, I'm at 79.9, so 10.1 degrees.
TC is 83.6, so 6.4 degrees (am I measuring this in a good spot?)
Drive shaft angle is 23.1.

Dropping the TC over an inch only seemed to net me a couple of degrees.
Weird question, would a worn TC mount be affecting my angle any?

I'd love to do an SYE coz I know that is the best fix. This is only a weekend exploring vehicle and something we take on vacation so no major wheeling. Is there a cost effect SYE kit with everything for that type of application?

Thanks again for all the help. I'm not quite ready to give up and go back to stock yet....LOL

 

[taylormade73]

Which TC skid is that? Doesn’t look stock. It may have tucked your TC higher causing a greater net DS angle than just from the lift. You may have to drop TC a couple of inches.

 

[Shawn at Tom Wood's]

Thanks for that info. Here's some new pics and angles
Measuring off the back of the diff, I'm at 79.9, so 10.1 degrees.
TC is 83.6, so 6.4 degrees (am I measuring this in a good spot?)
Drive shaft angle is 23.1.

These angles are pretty typical on a lifted TJ and certainly enough to cause angle related drive shaft vibrations. Unfortunately when people say you don't need an SYE with a 2" lift they are speaking subjectively. They maybe didn't need one but they might have been lucky and/or their jeep might just be all around noisier than yours and maybe they don't notice the vibrations as much or something like that. Whenever someone asks me what they need I say something like "Lets define that, what does it mean to you for things to 'work'? If you are happy as long as your Jeep moves forward when you press on the gas that will be pretty easy to achieve. If you want things to be as quit and smooth as a stock Jeep that's going to require a bit more effort"

Dropping the TC over an inch only seemed to net me a couple of degrees.
Weird question, would a worn TC mount be affecting my angle any?

I suppose it could but I don't know. Dropping the t-case does usually only net a couple degrees. Which is why I consider it to be a Band-Aid and not a cure. Sometimes it helps enough to make people happy but compered to the changes an SYE makes a t-case drop is almost insignificant.

Would it make sense to pull the rear drive shaft and go drive in 4 high and see if the vibration is gone? If I do is there anything I need to be careful about driving with the front drive shaft?

Probably. But now that I know all the angles I'm very confident telling you that it is indeed coming from the rear drive shaft.

I'd love to do an SYE coz I know that is the best fix. This is only a weekend exploring vehicle and something we take on vacation so no major wheeling. Is there a cost effect SYE kit with everything for that type of application?

There are some SYE kits online for just under $200. Just don't get a Hack And Tap SYE, the design on these sucks. Any kit that comes with a new output shaft, new yoke, and new housing should work well for you. There are different grades of quality between the manufacturers but they are all essentially teh same design. Sadly, when you add up the price of the SYE, drive shaft, and control arms you are looking at spending a minimum of $750.

Thanks again for all the help. I'm not quite ready to give up and go back to stock yet....LOL

You either have to accept the vibrations and get used to them, go back to stock height, or continue down the rabbit hole. Here's a good place to point out something I often think about and remark upon. Pretty much the whole Jeep aftermarket industry starts with one thing, people want bigger tires. Bigger tires mean a lift kit, which means an SYE, which means a drive shaft. Then you also need stronger axles because of the bigger tires, now you need different ring and pinion gears, now the motor could use an upgrade, and so on and so on until, for some people, they've spent $100,000. It all starts with "I should put bigger tires on my Jeep."

 

[jrockrat]

I did pull the rear shaft and took a drive just to see and it is for sure related to that.

The skid plate is a Barnes bolt on plate, I had forgot about that raising things up a little bit too.
From the Barnes website "This skid will raise the transmission mount up to 1", some transfer case linkage adjustments may be required. On Jeeps with over a 2 inch suspension lift height, a slip yoke eliminator is recommended to avoid drive line vibrations."

I was able to drop the TC about 1/2 inch with the stock bolts just to take it for a quick drive. It had a little less vibration.
I may try the stock skid plate with the 1/2 inch drop and see what that is like.
Also as a cheap band aide I think I might try some longer bolts and drop it a little bit more and see how it does, then I'll decide what to do.

If I could do the SYE, with drive shaft and control arms for $750 I might just bite the bullet. It doesn't look like too difficult of a task to do. I just have to decide my course of action quickly with vacation coming up.
Thanks again for all the direction and input.

 

[jrockrat]

I had done the aftermarket skid plate soon after buying the jeep and had forgotten it had added in TC height to it. Oh how these little details matter.
Quick follow up.....Stock skid plate with 3/8" drop got my TC angle to 81 (9 degrees) vs the 80 (10 degrees) at the rear. I had very little if any vibrations. I'm thinking of getting longer bolts to be safe and maybe drop the TC just a bit more and see what that does. That should get me through vacation. Then after that I can do things right at some point with the SYE set up.

Once again thanks to all that gave input, ideas, and experience.

 

[Woodrow]

So you have a tummy tuck. That “little detail” explains it .