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Discussion Starter #1
Specs.

2011 JKUR
TeraFlex Long Arm 4" lift
3.8l
Automatic
21,300 miles
5.13 gears.
Aftermarket Front and Rear drive shafts.
Toyo MT 35x12.5-17r Balanced-well taken care of.

We primarily only use her for off road travel and hardly ever run her over 65mph. Well cared for, well managed Jeep. Not trashed.

OK, now the issue.

The sound shows up only on a up hill run on pavement, seeing how I must be around 58 to start it and will end if I go over 70mph.

It will be a "womp" sound about every second or so speeding up taking approximately 50 seconds to become a static sound. When at full "sound" it is almost like a rubber on plastic sound mixed with a hollow vibration sound and not very loud.

This only happens on an up hill run no matter the incline. Does not matter what gear it is in. Only speed. Does not do it in 4wd low.

Yesterday when it first popped up, after inspecting everything and finding nothing odd, leaking, rubbing etc. Got her back up to speed and the sound returned, gently pressed on the brakes, the sound backed off and then quickly returned as we proceeded up the hill.

Got home, full inspection, nothing rubbing, nothing out of the ordinary. Went ahead and greased everything, drivelines and the suspension components. Drive lines feel tight, output shafts are solid, nothing leaking.

Hit the road this morning, first hill... Not a sound. However the second one it was back, I gently pressed on the brakes, sound just kept getting worse. We decided to let it run its full course to try and identify the sound. We failed at identifying it.

Here is what we know. Light "womp" sound. Can feel the sound in the steering wheel as it speeds up not us. Hill goes away, so does the sound. Pressing the brakes does nothing to end it HOWEVER, quickly putting it in 4wd will end it all together and make the event start all over.


/dawn flame suit :tomatoes:
 

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Some times a balance is not good enough. Extra attention needs to be put towards balancing bigger tires.
Were they road forced ?

Do you have a alignment sheet (caster angle) ?

Your rear driveline .. What's the DS angle compared to the differential ?
Torque up hill might have your rear DS operating at the wrong angle. -2* will prevent this- allowing the diff to raise under load.
 

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Specs. 2011 JKUR TeraFlex Long Arm 4" lift 3.8l Automatic 21,300 miles 5.13 gears. Aftermarket Front and Rear drive shafts. Toyo MT 35x12.5-17r Balanced-well taken care of. We primarily only use her for off road travel and hardly ever run her over 65mph. Well cared for, well managed Jeep. Not trashed. OK, now the issue. The sound shows up only on a up hill run on pavement, seeing how I must be around 58 to start it and will end if I go over 70mph. It will be a "womp" sound about every second or so speeding up taking approximately 50 seconds to become a static sound. When at full "sound" it is almost like a rubber on plastic sound mixed with a hollow vibration sound and not very loud. This only happens on an up hill run no matter the incline. Does not matter what gear it is in. Only speed. Does not do it in 4wd low. Yesterday when it first popped up, after inspecting everything and finding nothing odd, leaking, rubbing etc. Got her back up to speed and the sound returned, gently pressed on the brakes, the sound backed off and then quickly returned as we proceeded up the hill. Got home, full inspection, nothing rubbing, nothing out of the ordinary. Went ahead and greased everything, drivelines and the suspension components. Drive lines feel tight, output shafts are solid, nothing leaking. Hit the road this morning, first hill... Not a sound. However the second one it was back, I gently pressed on the brakes, sound just kept getting worse. We decided to let it run its full course to try and identify the sound. We failed at identifying it. Here is what we know. Light "womp" sound. Can feel the sound in the steering wheel as it speeds up not us. Hill goes away, so does the sound. Pressing the brakes does nothing to end it HOWEVER, quickly putting it in 4wd will end it all together and make the event start all over. /dawn flame suit :tomatoes:
What you describe is what happens if either the front pinion bearings are shot, the front pinion nut has loosened up, the front driveshaft slip splines have play, or the front transfer case output shaft bearings are shot.

It is common that people who run more than about 4.5 degrees caster with a 4" or taller lift end up damaging the things I listed above.

Put your front axle up on jack stands, then crawl under and twist the driveshaft, push and pull on the yoke at the pinion, check for side to side play of the pinion, check for play that indicates worn driveshaft slip splines, and do the same with the front transfer case output shaft.

You could also remove the front driveshaft to see if the vibration goes away to isolate the sources.
 

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Out of balance tires don't stop vibrations in 4wd or with slight braking.
 

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Discussion Starter #5
Going to take her apart tomorrow morning at our shop.

Ill start with pulling the Drive Shaft, doing a through inspection, check the nut and so on. Then run up the hill, see what it brings on.



Will update tomorrow.
 

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I think it is your driveshaft or pinion angle. Keep us posted.
 

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Discussion Starter #7
Ok. Got her back yesterday.

Rear Pinion angle was +5 degrees.

Rear drive line was out also. Move weight back 3/16" and 20 degrees.

I was present for the events that took place, solid job done by Jason at Absolute Offroad. She drives like a dream.
 

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Glad Jason got it taken care of! :bop:
 

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Some times a balance is not good enough. Extra attention needs to be put towards balancing bigger tires. Were they road forced ? Do you have a alignment sheet (caster angle) ? Your rear driveline .. What's the DS angle compared to the differential ? Torque up hill might have your rear DS operating at the wrong angle. -2* will prevent this- allowing the diff to raise under load.
Ok. Got her back yesterday. Rear Pinion angle was +5 degrees. Rear drive line was out also. Move weight back 3/16" and 20 degrees. I was present for the events that took place, solid job done by Jason at Absolute Offroad. She drives like a dream.
Oh yea baby :thumb:
 
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