The purpose of this thread is to provide a clearing house of information directly relevant to the the onset of high speed vibrations in a TJ/LJ Rubicon with 4.0l engine, 42RLE transmission and NP241OR transfer case after re-gearing to 4.88 or deeper gear sets..
Discussion of similar phenomena in jeeps with different transmissions, transfer cases or axles is a topic for another thread.
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My jeep: 2006 LJ Rubicon with 4.0l engine, 42RLE automatic transmission, 241OR transfer case, purchased from the prior owner with "metric 35" Mickey Thompson Baja ATZ P3 tires [315/75] and 4.88 gears. Currie Correctlync Steering, Currie Antirock Off-Road Swaybar, 5" lift.
My issue: After re-gearing from 4.88 to 5.38, I had a vibration or harmonic in or near the front end that began at exactly 67 mph and got worse as speed increased, enough so that if felt like it might vibrate my fillings loose when I tried to pass the 18 wheelers on the Interstate at 73 or above.
Posts on various jeep forums suggest that I am not the only one with this issue after re-gearing to 5.13 or 5.38. It appears to occur primarily (or only) in TJ's with the 42RLE automatic transmission and NP241OR transfer case.
My observations:
Immediately after the re-gear I noticed chirping from double cardan joint in the factory front driveshaft. The driveshaft was removed. I ordered a custom Tom Woods front driveshaft in lieu of rebuilding the u-joints in the factory unit. While waiting for a replacement no vibrations were noted.
The new driveshaft arrived in undamaged packaging and was installed. No vibrations were noted for several weeks because the gears were still new and during initial break-in I had been instructed to keep the speeds under 60. It wasn't until a few weeks after the new driveshaft was installed, after ring and pinion break-in was complete, that I drove faster than 65 mph and first noticed the vibration,which begins at exactly 67 mph and feels a lot like hitting a bad section of rain grooves in a concrete freeway. The vibration can only be felt through the steering wheel and not through the body, floor or shift levers. The vibration does not affect steering, which tracks straight and does not drift. The vibration does not increase much with increases in speed, if at all. Its there or its not.
The vibration did not change in mph at onset, character or intensity or any other way after any of the following:
a. Tire pressure adjustments
b. Re-balancing and rotating tires
c. Re-alignment (all within specs except caster, which was low as expected with a lifted rig)
d. Comprehensive professional inspection of all steering components, which are all tight, in good repair and well lubricated.
I had a telephone conversation with @mrblaine, who was aware of similar issues with other jeeps with 42RLE, 241OR and deep gears. He suggested that I check the front pinion angle and raise it if it was low.
My front pinion angle measured 10.5* My front driveshaft angle was 11.5*. The front [pinion angle was adjusted after which the front pinion angle and front driveshaft angle were both 11*.
I have only had time for an initial test drive. The vibration still comes on at exactly 67 mph but the intensity is considerably less after the pinion angle adjustment. I can now get up to 85 mph (as fast as I could go for the conditions that day) and the vibration isn't so bad that I want to immediately get off the throttle. However, there is still enough vibration to be an irritant at 67-75 mph cruising speeds.
I have a 300 mile round trip planned this coming weekend, which will give me ample time to record observations about how the pinion angle adjustment has changed the vibration. Its easy enough to avoid, just set cruise control at 65, but I would like to improve the situation after my return.
My plan is to raise the front pinion angle about 1/2* and observe any changes. Maybe the vibration will subside, maybe it will get worse, maybe it will stay the same.
If pinion angle adjustments can't fix this, I am open to any and all suggestions as to what to try next. I know I can "fix" it with money, i.e., converting to manual hubs, but I would like to try all the adjustments possible before I give up and go that route.
Your similar experiences?
What worked?
What didn't?
Discussion of similar phenomena in jeeps with different transmissions, transfer cases or axles is a topic for another thread.
______________
My jeep: 2006 LJ Rubicon with 4.0l engine, 42RLE automatic transmission, 241OR transfer case, purchased from the prior owner with "metric 35" Mickey Thompson Baja ATZ P3 tires [315/75] and 4.88 gears. Currie Correctlync Steering, Currie Antirock Off-Road Swaybar, 5" lift.
My issue: After re-gearing from 4.88 to 5.38, I had a vibration or harmonic in or near the front end that began at exactly 67 mph and got worse as speed increased, enough so that if felt like it might vibrate my fillings loose when I tried to pass the 18 wheelers on the Interstate at 73 or above.
Posts on various jeep forums suggest that I am not the only one with this issue after re-gearing to 5.13 or 5.38. It appears to occur primarily (or only) in TJ's with the 42RLE automatic transmission and NP241OR transfer case.
My observations:
Immediately after the re-gear I noticed chirping from double cardan joint in the factory front driveshaft. The driveshaft was removed. I ordered a custom Tom Woods front driveshaft in lieu of rebuilding the u-joints in the factory unit. While waiting for a replacement no vibrations were noted.
The new driveshaft arrived in undamaged packaging and was installed. No vibrations were noted for several weeks because the gears were still new and during initial break-in I had been instructed to keep the speeds under 60. It wasn't until a few weeks after the new driveshaft was installed, after ring and pinion break-in was complete, that I drove faster than 65 mph and first noticed the vibration,which begins at exactly 67 mph and feels a lot like hitting a bad section of rain grooves in a concrete freeway. The vibration can only be felt through the steering wheel and not through the body, floor or shift levers. The vibration does not affect steering, which tracks straight and does not drift. The vibration does not increase much with increases in speed, if at all. Its there or its not.
The vibration did not change in mph at onset, character or intensity or any other way after any of the following:
a. Tire pressure adjustments
b. Re-balancing and rotating tires
c. Re-alignment (all within specs except caster, which was low as expected with a lifted rig)
d. Comprehensive professional inspection of all steering components, which are all tight, in good repair and well lubricated.
I had a telephone conversation with @mrblaine, who was aware of similar issues with other jeeps with 42RLE, 241OR and deep gears. He suggested that I check the front pinion angle and raise it if it was low.
My front pinion angle measured 10.5* My front driveshaft angle was 11.5*. The front [pinion angle was adjusted after which the front pinion angle and front driveshaft angle were both 11*.
I have only had time for an initial test drive. The vibration still comes on at exactly 67 mph but the intensity is considerably less after the pinion angle adjustment. I can now get up to 85 mph (as fast as I could go for the conditions that day) and the vibration isn't so bad that I want to immediately get off the throttle. However, there is still enough vibration to be an irritant at 67-75 mph cruising speeds.
I have a 300 mile round trip planned this coming weekend, which will give me ample time to record observations about how the pinion angle adjustment has changed the vibration. Its easy enough to avoid, just set cruise control at 65, but I would like to improve the situation after my return.
My plan is to raise the front pinion angle about 1/2* and observe any changes. Maybe the vibration will subside, maybe it will get worse, maybe it will stay the same.
If pinion angle adjustments can't fix this, I am open to any and all suggestions as to what to try next. I know I can "fix" it with money, i.e., converting to manual hubs, but I would like to try all the adjustments possible before I give up and go that route.
Your similar experiences?
What worked?
What didn't?