Do I need to adjust pinion angle with a 3" lift?


Fargo

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I have a 2005 LJ Rubicon with a 6 speed manual transmission. Last summer I installed adjustable control arms, and set them at the same length as my factory control arms were. Earlier this summer I swapped out my 2" springs for some 3" JKS coils. I hadn't noticed any vibes until this week. Driving into town on the Interstate with my wife and kids, I thought I had noticed some vibes. About that same time, my wife commented that she heard a rhythmic vibration. It seemed to come and go about every 2-3 seconds. It only did it at a very specific interstate speed. Tonight I went for a long drive to try and duplicate the sound. At about 78-80 MPH I could just faintly hear something. It was not as noticeable as when I had the Jeep loaded down with the family, but I think I could still hear something very faint if I really listened for it. I do have BFG KM2 MT tires, so they could cause some vibration, but they are prettly low milage tires and I have rotated them regularily, so they are still pretty quiet.

So with all that said. Do I need to adjust my pinion angles. Or is this a normal harmonic vibration that is not cause for concern.
 

Chris

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If you have adjustable control arms that suggests that you have (or should have) a double cardan driveshaft. If so, then yes, you do need to adjust your pinion angles.
 

bobthetj03

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It's striking how much the pinion angle changes just from an empty fuel tank to a full one. You may need to make some minor adjustments to the rear pinion just to keep it in a semi happy place. It's a slippery slope, and some of us are more sensitive to the harmonic than others. Hard tops seem to amplify the harmonic.
 

Rubicon88

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I'm thinking tires.

Think about your cargo(family) weighing the jeep down and the vibe being worse.

The Jeep squatting a bit from weight would help your pinion angles more than empty..which empty would have a tad steeper angle diff yoke to t-case yoke.

On the flip side your tire vibe/noise would increase with more weight versus empty.

Good luck.

P.s. how many miles on the tires?
 
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Fargo

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The tires have 18,000 miles on them. They are starting to get a little louder than they were new. But they are still pretty quiet. The noise wasn't a constant hum though. It was more cyclical. Can tires do that?

I was thinking about the extra weight as well, but I was wondering if it was putting extra force on the driveline and increasing any vibes due to the extra weight and torque put on the drivetrain. Then again, how much of a difference is 500lbs worth of people in a 5000lbs Jeep?

I do NOT have a double cardon driveshaft. It is the stock driveshaft on the LJ Rubi. The arms are currently all at stock length.

Thinking about the video in this thread, https://wranglertjforum.com/threads/harmonic-vibrations-in-jeeps-a-new-theory-please-read.15144/ I was wondering which way to adjust my pinion. I know its not the normal procedure, but it seems to me that I should tip the front back down toward the road. That would put it closer to the stock position and make the angles more parallel again. But it would also put more angle on the ujoints.

My vibration was very minimal and it was such a rare occurance, I am not concerned about it for comfort or NVH reasons. Most poeple would never even notice the vibe. My concern is if this minor vibe could damage ujoints or seals or bearings or something even more critical like the transfer case itself. My biggest concern is protecting my equipment. But thats not to say I don't want to eliminate the vibe for comfort reasons. But if its not going to slowly destroy my Jeep the time and money I put into the issue will be a bit less.
 

Rubicon88

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The tires have 18,000 miles on them. They are starting to get a little louder than they were new. But they are still pretty quiet. The noise wasn't a constant hum though. It was more cyclical. Can tires do that?

I was thinking about the extra weight as well, but I was wondering if it was putting extra force on the driveline and increasing any vibes due to the extra weight and torque put on the drivetrain. Then again, how much of a difference is 500lbs worth of people in a 5000lbs Jeep?

I do NOT have a double cardon driveshaft. It is the stock driveshaft on the LJ Rubi. The arms are currently all at stock length.

Thinking about the video in this thread, https://wranglertjforum.com/threads/harmonic-vibrations-in-jeeps-a-new-theory-please-read.15144/ I was wondering which way to adjust my pinion. I know its not the normal procedure, but it seems to me that I should tip the front back down toward the road. That would put it closer to the stock position and make the angles more parallel again. But it would also put more angle on the ujoints.

My vibration was very minimal and it was such a rare occurance, I am not concerned about it for comfort or NVH reasons. Most poeple would never even notice the vibe. My concern is if this minor vibe could damage ujoints or seals or bearings or something even more critical like the transfer case itself. My biggest concern is protecting my equipment. But thats not to say I don't want to eliminate the vibe for comfort reasons. But if its not going to slowly destroy my Jeep the time and money I put into the issue will be a bit less.
Its extremely hard to try and help with noises on a message board. Add to that everyone's ears are different and so on....

Your tires aren't directional so criss cross them in an x pattern and try to duplicate. If the vibe/noise changes...louder, lightens, etc....there you go.
Simple way to eliminate a possible...or confirm.

Good luck
 
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Fargo

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I found this comment while reading through some old documents I saved from Nth Degree. I don't have the Double Cardon drive shaft, but I think it might still give me some insight. I'll need to measure some angles and see what I have. But the comment about feeling the vibes under load is what jumped out to me.

3) Driveshaft Angles. I assume you have a double-Cardan (aka ‘CV’) rear driveshaft.
Even so, if you have substantial angle at that rear DC joint, it *can* create vibes under
load since it’s not really a ‘Constant Velocity’ joint - typically these non-constant-effects
are subtle and you don’t notice them, but at 15+ degree operating angles under heavy
load, you might.

I'm not sure what I'm doing yet, so I'll keep researching. Thanks for the help. If anyone else has any ideas let me know.
 

Jerry Bransford

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Adjusting your pinion angle isn't the approach I'd take. That is because with the factory rear driveshaft, your rear pinion angle (the front wouldn't cause this problem) needs to remain parallel to the output shaft of your transfer case. Adjusting the pinion angle would cause those two shafts to no longer be parallel to each other.

The problem that is causing your vibrations is due to the driveshaft's u-joints now working into an excessive angle caused by the taller suspension lift. It is the u-joints that are vibrating and it's best to get this resolved ASAP so the u-joints won't be damaged.

There are three fixes to reducing/eliminating the excessive angles the driveshaft's u-joints are working into, any of them will work. The cheapest is 1) to drop the transfer case skidplate 1/2" to 1" via spacers placed between the skidplate and frame. 2) Install a pair of rubber 1" motor mount lifts. 3) Replace the factory rear driveshaft with a CV (double-cardan) driveshaft. That however would also require adjustable length upper/lower control arms because a CV driveshaft would indeed require the pinon angle be raised so it is the same angle as the driveshaft.

This first illustration is for your factory driveshaft...

2joint_angle.jpg


This is how it would need to look with an aftermarket CV (double-cardan) driveshaft.

cv_angle.gif
 
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Fargo

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Adjusting your pinion angle isn't the approach I'd take. That is because with the factory rear driveshaft, your rear pinion angle (the front wouldn't cause this problem) needs to remain parallel to the output shaft of your transfer case. Adjusting the pinion angle would cause those two shafts to no longer be parallel to each other.

Why wouldn't the front cause this problem? With an LJ the shafts are very similar in length.

In regards to the rear pinion angle needing to remain parellel to the output shaft, that is why I thought I might need to tip the pinion back down. I didn't take a measurement when I lifted the Jeep, but I am pretty sure that when I lifted the Jeep, the pinion did rotate upwards slighlty and now points more towards the transfer case than it did at stock height. In which case my pinion is no longer parellel with the output shaft. So I thought it would be slightly out of phase and thus causing the vibration. In that case it needs to be pointed back down. Of course the problem with this solution is that if I tip the pinion back down I increase the angle on the u-joints. So which is the greater evil. Having more bind on the u-joint or having the driveshaft slightly out of phase due to differences in pinion angle relative to the angle of the output shaft.



The problem that is causing your vibrations is due to the driveshaft's u-joints now working into an excessive angle caused by the taller suspension lift. It is the u-joints that are vibrating and it's best to get this resolved ASAP so the u-joints won't be damaged.

As mentioned above, I question if it is the u-joints binding or is it because my pinion and my output shafts are no longer parallel after the lift. I have an LJ so my u-joints are not at a very steep angle. It doesn't seem like they should be binding. But they might be out of phase.

Does that make sense?
 

Jerry Bransford

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The front driveshaft already has a CV joint, the rear does not.

If you think the u-joints are out of phase, just check that the u-joints are lined up. If they were simply out of phase you would have had vibrations at 2.5" too. I'm sticking with my original recommendations above.
 
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Fargo

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The front driveshaft already has a CV joint, the rear does not.

I wondered about that. Guess I should have crawled under there and looked at it before I asked. Thanks for being kind in your response.

If you think the u-joints are out of phase, just check that the u-joints are lined up. If they were simply out of phase you would have had vibrations at 2.5" too. I'm sticking with my original recommendations above.

Sorry, that was my mistake to say out of phase. That is something different. What I meant to say was simply that after the lift, I don't think my driveshaft has a uniform velocity. Your diagram above is good. If I had to draw a diagram of my current setup, I think it would look similar to the stock 2 joint setup above. However, because our control arms do not keep the pinion perfectly level when the Jeep is lifted, the front of my pinion is now pointing slightly upward. Not as far as it would be if I had a CV driveshaft in the 2nd diagram, but it is tipped up enough that it is no longer parallel. Now this would have also happened with my 2" lift as well, but it would have been to a lesser extent. So that is why I was wondering if I should tip the front of the pinion back down. Tipping the pinion down would get the angles of my pinion and output shaft closer to parallel again as they are in the first picture. I may not be able to achieve perfect parallel, but it would be closer. Albeit at the expense of more driveshaft angle and more bind on the u-joints.

If you watch this video you will see the problem I am trying to describe illustrated at the 50 second mark. The solution appears at about 1:30. This is an extreme example, but it shows what happens if the pinon is not parallel with the output shaft.


This is what I expect might be happening in my case. That is why I wonder if tipping the pinion down is a viable solution. The only drawback I see is that the u-joints are at an even greater angle.
 

Jerry Bransford

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Again, changing the rear pinion angle is NOT the fix. Doing that would give you two problems... the pinion and tcase output shaft angles are no longer parallel and it would make the rear u-joint's operating angle even worse.

THe 3 fixes I described are what I'm sticking with. What you have is a common problem, the fixes are well known and changing the rear pinion angle is not one of them.
 
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Fargo

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Again, changing the rear pinion angle is NOT the fix. Doing that would give you two problems... the pinion and tcase output shaft angles are no longer parallel and it would make the rear u-joint's operating angle even worse.

Thank you Jerry for helping out. I know your knowledge of the Jeep world is far greater than mine. So I'm not trying to argue, I'm just a little confused as to why you think that my pinion angle and transfer case output shaft are still parallel. They were parallel when the Jeep was stock, but when the Jeep was lifted those angles changed. At least I think they changed. I've never been able to get an accurate reading on my angle finder. But as far as I can tell they are off by about 2-5 degrees. So that is why I keep thinking I need to tip the pinion back down. I'm just trying to get back to parallel. I'll have to get a more accurate angle finder though to see if I can get a better reading on those angles. So I'll have to get back to you on this. Thank you for your help. You've provided good information and things to think about.
 

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The tires have 18,000 miles on them. They are starting to get a little louder than they were new. But they are still pretty quiet. The noise wasn't a constant hum though. It was more cyclical. Can tires do that?

I was thinking about the extra weight as well, but I was wondering if it was putting extra force on the driveline and increasing any vibes due to the extra weight and torque put on the drivetrain. Then again, how much of a difference is 500lbs worth of people in a 5000lbs Jeep?

I do NOT have a double cardon driveshaft. It is the stock driveshaft on the LJ Rubi. The arms are currently all at stock length.

Thinking about the video in this thread, https://wranglertjforum.com/threads/harmonic-vibrations-in-jeeps-a-new-theory-please-read.15144/ I was wondering which way to adjust my pinion. I know its not the normal procedure, but it seems to me that I should tip the front back down toward the road. That would put it closer to the stock position and make the angles more parallel again. But it would also put more angle on the ujoints.

My vibration was very minimal and it was such a rare occurance, I am not concerned about it for comfort or NVH reasons. Most poeple would never even notice the vibe. My concern is if this minor vibe could damage ujoints or seals or bearings or something even more critical like the transfer case itself. My biggest concern is protecting my equipment. But thats not to say I don't want to eliminate the vibe for comfort reasons. But if its not going to slowly destroy my Jeep the time and money I put into the issue will be a bit less.
No, don’t adjust your pinion bc you don’t have a SYE and DC. Between 2 and 3” is a guessing game. If you don’t have a MML, I bet that would take care of your vibes. Or you can do a TCase drop. The expensive, but best way is a SYE and DC.
 

Jerry Bransford

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Thank you Jerry for helping out. I know your knowledge of the Jeep world is far greater than mine. So I'm not trying to argue, I'm just a little confused as to why you think that my pinion angle and transfer case output shaft are still parallel. They were parallel when the Jeep was stock, but when the Jeep was lifted those angles changed. At least I think they changed. I've never been able to get an accurate reading on my angle finder. But as far as I can tell they are off by about 2-5 degrees. So that is why I keep thinking I need to tip the pinion back down. I'm just trying to get back to parallel. I'll have to get a more accurate angle finder though to see if I can get a better reading on those angles. So I'll have to get back to you on this. Thank you for your help. You've provided good information and things to think about.
The installation of a suspension lift, by itself, does not affect the transfer case angle neither does it affect an axle's pinion angle.
 

jodomcfrodo

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The relative angle hasn’t changed, which is all that matters without a CV shaft.

How bad are your vibes? Barely being able to notice them without really trying at 70 or 80 doesn’t indicate anything crazy to me personally. If the same setup has worked previously and just started to vibe, I would look at the ujoints first. Could be a simple fix.

Afterwards, I would start with an MML if you think you’re having vibes. Though, you are just a driveshaft away from having a nice and proper setup considering you have a rubicon and adjustable arms, so that is something to consider.
 
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Fargo

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The installation of a suspension lift, by itself, does not affect the transfer case angle neither does it affect an axle's pinion angle.

The relative angle hasn’t changed, which is all that matters without a CV shaft.

Thank you gentleman. I'm going to have to do some jacking around on the Jeep and watch the pinion. I could have sworn the angles changed when I lifted it. But if I am wrong on this, then my whole theory is wrong. And if that is indeed the case, Jerry already provided multiple solutions for fixing vibes.


How bad are your vibes? Barely being able to notice them without really trying at 70 or 80 doesn’t indicate anything crazy to me personally. If the same setup has worked previously and just started to vibe, I would look at the ujoints first. Could be a simple fix.

Afterwards, I would start with an MML (Motor Mount Lift) if you think you’re having vibes. Though, you are just a driveshaft away from having a nice and proper setup considering you have a rubicon and adjustable arms, so that is something to consider.

The vibes are very minimal. I only noticed them one day cruising down the Interstate. I tried to replicate my speed and everything again later, but I was not able to repeat the event and produce the vibes again. Even listening for them I could only 'maybe' barely hear them. So on a typical day I do not have any vibes. But I did notice them one time, so I figured something wasn't right. I just wanted things to be perfect. Maybe I don't need to do anything at all. Thanks for all the help.
 

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... I've never been able to get an accurate reading on my angle finder. But as far as I can tell they are off by about 2-5 degrees. ...


You can measure the pinon off of the case spreader flat spots on either side of the diff cover. You can measure the rear output angle off of any surface along the drivetrain that is parallel or perpendicular to the output.
 
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AndyG

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Its extremely hard to try and help with noises on a message board. Add to that everyone's ears are different and so on....

Your tires aren't directional so criss cross them in an x pattern and try to duplicate. If the vibe/noise changes...louder, lightens, etc....there you go.
Simple way to eliminate a possible...or confirm.

Good luck
This first line is a very very true statement. Another thing is this is pretty hard in person... It has amazed me how hard it can be to tell where the noise is coming from.

I would pull the front drive shaft and rotate the tires before I did anything.

I would see if a drive shaft weight may have fell off.

You can get under the jeep with an angle finder and test it loaded and unloaded and see if you're pretty close on your opinion angle which needs to be parallel or a tad below your output shaft.

Since torque load moves the the pinion up it is considered that a degree below is considered a good thing.

Reading a little more into it...just the fact that you can drive the vehicle with your family in it 70 to 80 tells me it's in pretty good shape.

Keep us posted when you learn things in situations like this, we all do.
 
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Fargo

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Thanks guys.

jjvw - I never thought about looking at the back side of the differential for a place to measure angle. That will help.

AndyG - I'll have to do like you said and get under the Jeep and take some angle measurements with it loaded and unloaded. Its interesting that you said that loading the vehicle pushed the pinion up. Since that would mean that lifting it pushes the pinion down. That is completely the opposite from what I thought was happening. If I can get reliable measurements of the rear of the differential were jjvw said to check, this will be interesting to check.

I think I have gotten some very good information from everyone here. Now all I can do is start measuring my angles, observe how the pinion moves when loading the Jeep, swap tires, check weights etc and listen for any vibes.

The most difficult thing on the list is probably hearing the vibes. They are that faint except for that one time. So I need to do more driving and testing with it loaded and unloaded since that is when I hear the vibes.

Maybe I am seeking after too much perfection. As you said my Jeep is in pretty good shape. I can drive on the Interstate at 80-85 MPH all day long and feel the vehicle is stable and in control. In fact, I do that very thing every couple years when I load up the family and drive to 1200 miles to the mountains of Colorado. My Jeep was built to handle Interstate speed safely and still provide the offroad capability on mild to medium trails. But in pursuing that goal, it is also the reason why I don't want any vibes.

Thanks again to everyone for all the help. I'll do some testing and observing as everyone mentioned and see if I can figure things out.