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Old 07-13-2015, 10:06 PM
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Help with Vibration

I could use some advice from the forum. I am getting some vibration when going about 70mph or faster, which I can feel not in the steering column, but in my seat. It's not horrible, but it's there and new.

Some background: I have a 2012 JKUR on which I put some 315 tires and wheels about 5 weeks ago, followed by a Tom Woods drive shaft about a month ago, followed by a Rock Krawler 3.5" x-Factor lift about 3 weeks ago, and then regearing by a local shop from 3.73 to 4.56 a little over a week ago. So lots of changes, but it was after the regearing over the weekend that I first noticed the vibration.

I've been doing some reading trying to diagnose the source of the vibration. One potential source I researched is a driveshaft out of balance which is spinning faster from the regear. I suppose that is possible, but I wouldn't expect that of a new Tom Woods driveshaft. But I may pull it out and drive without it to check.

Another might be tires. They are Mickey Thompson ATZ P3s. When I had them mounted and balanced, I elected to just have the weights on the inside of the wheels, rather than both sides, and the shop mentioned they wouldn't balance as well with just inside weights. I could get them rebalanced. I did rotate the tires yesterday without any improvement.

Any chance the regear itself might cause this? The gears seem fine and don't make any noise that I can hear.

So, I'm just looking for a little sage advice how to go about figuring this out in a sensible way, and if there is anything other potential cause I haven't thought of. Thanks!

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Old 07-13-2015, 10:26 PM   #2
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Pretty easy to eliminate the drive shaft. If it were me I would try that first to help narrow it down before thinking gears. Tires would have at least some vibration in the steering wheel I would think.

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Old 07-13-2015, 11:03 PM   #3
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Ditto I got the vibration also 4.88 RK lift etc actually just like you minus the mickeys and driveshaft, is it a constant vibration or more of a come and go but repetitive and in a pattern? Mine ended up being a little of both, tires and driveshaft, pulled the front ds and rotated the tires. I have nittos and they get bad when not rotated. I didn't notice the vibration until after the gears so driveshaft was a pretty safe bet.
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Old 07-13-2015, 11:07 PM
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Thanks for the feedback. Mine is a consistent vibration above 70mph. I think I will pull the front driveshaft and see what happens.
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Old 07-13-2015, 11:12 PM   #5
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What are your caster numbers up front? Pinion angle in the rear? Pics may help also.

And yes, lower gearing can contribute to vibrations.
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Old 07-13-2015, 11:25 PM
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What are your caster numbers up front?
Pinion angle in the rear? Pics may help also.

And yes, lower gearing can contribute to vibrations.
Hi Ken. I had an alignment done after the lift and got 3.2 caster. I know, a little low, but the steering seemed fine so I didn't change it yet. Does regearing require a new alignment?

If I measured the rear pinion correctly, I got 9 degrees. I could send pics tomorrow if that would help.
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Old 07-14-2015, 12:53 AM
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Looking at the rear a bit more, it does look like the pinion is about 9 degrees, and the driveshaft a bit less - about 7.5 degrees. Should I shorten the rear upper control arms to reduce the pinion?
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Old 07-14-2015, 09:39 AM   #8
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Originally Posted by davidski View Post
Looking at the rear a bit more, it does look like the pinion is about 9 degrees, and the driveshaft a bit less - about 7.5 degrees. Should I shorten the rear upper control arms to reduce the pinion?
I think you mean that the other way around right? The driveshaft should be steeper then pinion, On a side note I have a tendency to mis inform on rears so we'll wait for Ken..... Mine wasn't a constant vibe and I had it at about 60 then the faster you went the fainter it got. Do you have some pictures you can post? side shot of the angles in the rear?
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Old 07-14-2015, 11:37 AM
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I think you mean that the other way around right? The driveshaft should be steeper then pinion, On a side note I have a tendency to mis inform on rears so we'll wait for Ken..... Mine wasn't a constant vibe and I had it at about 60 then the faster you went the fainter it got. Do you have some pictures you can post? side shot of the angles in the rear?
I'll double check after work tonight, but that's what I got - with the pinion a bit steeper than the driveshaft. Like you say, I think the pinion angle should be about 2 degrees less than the driveshaft angle. I have adjustable control arms, so that is fixable. I'll try to get a photo or two as well.
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Old 07-14-2015, 12:17 PM   #10
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Originally Posted by davidski View Post
I'll double check after work tonight, but that's what I got - with the pinion a bit steeper than the driveshaft. Like you say, I think the pinion angle should be about 2 degrees less than the driveshaft angle. I have adjustable control arms, so that is fixable. I'll try to get a photo or two as well.
I look at it like the pinion at 90* would be 0 and the driveshaft would have an angle, as you turn the diff up the pinion angle is going up and the driveshaft angle is going down. So you may be correct I just look at angles a bit different. So if you start with 10* on driveshaft and 0* on pinion as you turn the diff it goes 10-0 9-1 8-2 7-3 6-4 etc so when you say 7.5-9 I picture the pinion over the driveshaft...if that makes sense?? Also that scale isn't correct I was just trying to explain. But that shows 1.5* and your right RK told me 2-3* pinion... I went with around 2*. Im not sure of adverse affects but at 1.5* in the right direction anyways will be better on the driveshaft, I just don't know what that does for drivability in the rear.
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Old 07-14-2015, 02:11 PM   #11
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Fronts fine .. Lower caster means better pinion.
The rear is between the pinion/DS.
I would shorten the uppers, shoot for -2° difference.
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Old 07-14-2015, 04:34 PM
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Thanks for confirming my thoughts Ken, I'll shorten the rear uppers. It might have to wait until the weekend.

Thanks too for your input jwalters, appreciate it!
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Old 07-14-2015, 06:18 PM   #13
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As you work through this I would appreciate an update. I am having what sounds like the exact same issue. No vibration whatsoever until 70 mph and then all of a sudden it feels like I am on a washboard road (slight exaggeration). Not felt in the steering wheel, but in the seat. Unfortunately I did it all at once, lift, tires, gears, and drive shafts so I don't have the foggiest idea where to start. The vibration remains constant above 70 mph (at least up to 85-90 mph), which lead me to conclude an out of balance rear tire(s)? I have been told that drive shaft vibrations typically come on gradually, and possibly dissipate at higher speeds? I haven't rotated them yet, but it is on my to-do list. The original shop actually mounted the rear tires wrong side out (not very noticeable on the Nittos), so those will be getting remounted and balanced anyway.
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Old 07-14-2015, 11:35 PM
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I am discovering just how hard it can be to get good measurements of angles. Today I used my iPhone with an app, as carefully as I could. It felt more accurate to me. The pinion was 7 degrees and the driveshaft 6.4 degrees. This does confirm my general impressions that the pinion and driveshaft were close to perfect alignment.

I'll adjust the pinion to be about 2 degrees less than the driveshaft if that is recommended, but will that reduce vibration?
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Old 07-15-2015, 03:36 PM   #15
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Anything outside of recommended seems like a culprit for vibration or noise with jeeps. Do you have a 2-door? I agree pulling in the uppers a little might help, that driveshaft is way to happy lol.
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Old 07-16-2015, 11:24 PM
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I shortened my rear upper control arms, just guessing on how much to shorten, and when I got things together again I got a 6.9 degrees for the pinion and 8.6 degrees for the driveshaft, a difference of 1.7 degrees. Pretty darn close to 2 degrees. Photo of that is below.

I then went out for a short test drive. The vibration over 70mph was still there, although I think somewhat reduced.

So I am open to suggestions what I might do next. I am tempted to have the tires balanced again, and might remove the front driveshaft to see what affect that has.

This is for a 4 door Rubicon.
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Old 07-18-2015, 01:38 PM
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OK, this morning I removed the front drive shaft (after removing the skid plates in the way, argh) and took another test drive. Vibration was gone. Well, except for a bit I would consider normal vibration from the road which would come and go, but that is very little compared with before. The vibration I had, presumably from the front drive shaft, was much more pronounced, and I failed to mention before also came with a noticeable low hum sound, which now is also gone.

So, with the problem now isolated to the front drive shaft, I need to figure out what to do. Installation error? Drive shaft out of balance? I probably will talk with Tom Woods on Monday.

Two other things I noticed. Around the connection of the drive shaft to the flange of the transfer case, I noticed some oil sprayed around on the carriage. Seems to be a small leak there. No idea if this has anything to do with the vibration.

I also noticed a small ring of wear on the drive shaft in the vicinity of the crossover exhaust. I thought with the smaller diameter drive shaft that a spacer kit was not needed, but it appears it is. And I've barely been off road so far, so I definitely need to take care of that. Darn the extension of this 3.5" lift! :-)
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Old 07-18-2015, 03:13 PM
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Yeah Ken, that's my assumption too. And it makes sense the vibration wouldn't show up until I regeared and it began to spin faster. At least now I know what it is.

Originally my wife and I were planning our summer trip to Colorado a week from now. Glad we rescheduled that for the end of August!
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Old 07-26-2015, 10:55 AM   #20
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Yeah Ken, that's my assumption too. And it makes sense the vibration wouldn't show up until I regeared and it began to spin faster. At least now I know what it is.

Originally my wife and I were planning our summer trip to Colorado a week from now. Glad we rescheduled that for the end of August!
Were you able to re-balance the drive shaft? I took ours in and found the original shop never balanced the front tires (no weights and way off)... also got an alignment and found the toe was out of spec. Fixed all the vibration and pulling issues.

Edit: I have the same exhaust contact with my JE Reel shaft... I was told by others with the same issue to dent or remove the heat shield. I don't want to deal with spacers as they will cause other issues with my skids, but I haven't had a chance to test the fix yet.
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Old 07-26-2015, 12:54 PM   #21
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OK, this morning I removed the front drive shaft (after removing the skid plates in the way, argh) and took another test drive. Vibration was gone. Well, except for a bit I would consider normal vibration from the road which would come and go, but that is very little compared with before. The vibration I had, presumably from the front drive shaft, was much more pronounced, and I failed to mention before also came with a noticeable low hum sound, which now is also gone.

So, with the problem now isolated to the front drive shaft, I need to figure out what to do. Installation error? Drive shaft out of balance? I probably will talk with Tom Woods on Monday.

Two other things I noticed. Around the connection of the drive shaft to the flange of the transfer case, I noticed some oil sprayed around on the carriage. Seems to be a small leak there. No idea if this has anything to do with the vibration.

I also noticed a small ring of wear on the drive shaft in the vicinity of the crossover exhaust. I thought with the smaller diameter drive shaft that a spacer kit was not needed, but it appears it is. And I've barely been off road so far, so I definitely need to take care of that. Darn the extension of this 3.5" lift! :-)
I have the kid's doing the same thing. I have removed the front driveshaft until I can get her to park it long enough to better diagnose. She has an aftermarket front DS. I think it needs balancing.

Bob K.
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Old 07-27-2015, 10:43 AM
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Were you able to re-balance the drive shaft?
I sent it in to Tom Wood last week. They said it did need a bit of "straightening," which sounds different from balancing, but I didn't get that clarified. It'll be back tomorrow and I have my fingers crossed this will solve the issue. I'll post when I do.

I also picked up some exhaust spacers and put them in. I can see how the exhaust is lower and comes close to my skids now. If it's in the way, hopefully I still have a shim Rock Hard provided with skids for that purpose.
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Old 07-29-2015, 12:23 AM
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OK, so here's my follow-up.

I got the driveshaft back this evening, bolted it in and took a test drive on the highway. I wouldn't say it was perfect, but it was much improved. The vibration was just about gone - I may have felt the smallest amount around 75mph. There was still a bit of a hum sound around 73-75mph, but it was much reduced compared to before.

So, I need to drive it around for awhile, but I think it'll be fine now, or at least good enough. Do these things "break in" and get smoother in time? :-) My thanks to Tom Wood for the quick turnaround.

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