"Pacing myself" build

JMT said:
That bag, or one like it, was on my Christmas list. It’s still there. What’s your report on it? Is it quiet going down the road? Does it stay put?
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I'm pretty happy with it. It does stay put and is quiet as long as you have it packed so stuff doesn't rattle around. I've got 35lbs. worth a recovery gear stuffed in it. It rests on the wheel well, which also helps keep it quiet. I'll be getting another one for the other side soon.
 
Alex01 said:
I am watching wheeler dealers on my dvr and they started talking about harmonic vibrations. The new mechanic said they could be caused by the harmonic balancer on the crankshaft. Instantly I thought of your issue.

Figured it was worth passing on.

Also, I like the bottle opener. My mother in law gave me an old one her father used to use way back when a few weeks ago. I told her I was going to mount it on the bumper. I guess great minds think alike.
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We talked about the harmonic balancer in our vibe thread. @psrivats actually had his replaced in his efforts to quell the vibes, but I think my harmonics are being caused by drivetrain rotation making a resonant harmonic with the tub . I have driven a down slope on the freeway and put it in neutral and coasted trying to factor out the engine rpms as a culprit. Coasting in neutral changed nothing, so I don't think it is the engine playing a tune. the drive lines, tc, and diffs however are rotating at speed. At some point I'll probably replace the balancer simply because it's got 167K miles on it. In my efforts of replacing shit, my biggest improvement to date was after replacing the tc skid with the thicker Barnes skid, and sending my front ds to Tom Woods for a better balance. May end up doing the same for rear ds to see if I can gain more progress. I think it's just about trying to change the resonant frequency between the now faster spinning drive train, and the tub of the jeep. @psrivats vibes and mine have different culprits me thinks, but he gained improvement by adding an additional 170 mils of sound deadening to the inside of the tub. I have the 80mil stuff on mine, so I may add the 170 mil stuff on top of that. I also still have the rear yoke to replace to rule that out. Tough finding the time to work on the turd.
 
bobthetj03 said:
We talked about the harmonic balancer in our vibe thread. @psrivats actually had his replaced in his efforts to quell the vibes, but I think my harmonics are being caused by drivetrain rotation making a resonant harmonic with the tub . I have driven a down slope on the freeway and put it in neutral and coasted trying to factor out the engine rpms as a culprit. Coasting in neutral changed nothing, so I don't think it is the engine playing a tune. the drive lines, tc, and diffs however are rotating at speed. At some point I'll probably replace the balancer simply because it's got 167K miles on it. In my efforts of replacing shit, my biggest improvement to date was after replacing the tc skid with the thicker Barnes skid, and sending my front ds to Tom Woods for a better balance. May end up doing the same for rear ds to see if I can gain more progress. I think it's just about trying to change the resonant frequency between the now faster spinning drive train, and the tub of the jeep. @psrivats vibes and mine have different culprits me thinks, but he gained improvement by adding an additional 170 mils of sound deadening to the inside of the tub. I have the 80mil stuff on mine, so I may add the 170 mil stuff on top of that. I also still have the rear yoke to replace to rule that out. Tough finding the time to work on the turd.
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Did you see Mr.Bill's write up?

OK. Here are some data points:

06' LJ Rubicon, 4.0L motor, 42RLE Transmission, NV241OR transfer case, approx 5" actual lift - RE long arm with RE crossmember/skid plate, 35" tires (actual 34.6"), equipped with 4.88 gears at acquisition, no vibrations/harmonics. After re-gear to 5.38:1 vibrations/harmonic barely detectable at 60 mph, like turning a switch "on" at 67-68 mph (calibrated speedometer). Vibrations/harmonics did not change in character/intensity as speeds increased over 67-68, substantially reduced below that speed, undetectable below 60 during deceleration. Removal of front double cardan driveshaft = no vibrations at any speed. Installed new Tom Wood front driveshaft because center joint worn and chirping. Repeated tests - no change other than chirping being gone. Change in front pinion angle = bad vibration if front pinion angle lower than front driveshaft angle, gradually reduced as pinion angle matched to driveline angle and reduced slightly more with front pinon 1 degree higher than driveline angle. However, caster was reduced so much at that angle that steering was slow to return to center. The maximum I could adjust the front pinion angle was 1.5 degrees above driveline angle before lack of return to center became objectionable. Stopped experimenting at that point and addressed problem by converting to manual hubs. Issue resolved.
 
What about some kind of rubber welting between the skid plate and the frame? I read somewhere about this possibility. Just a thought, though I'd say its nickel and dime thought
 
lowranger said:
Did you see Mr.Bill's write up?

OK. Here are some data points:

06' LJ Rubicon, 4.0L motor, 42RLE Transmission, NV241OR transfer case, approx 5" actual lift - RE long arm with RE crossmember/skid plate, 35" tires (actual 34.6"), equipped with 4.88 gears at acquisition, no vibrations/harmonics. After re-gear to 5.38:1 vibrations/harmonic barely detectable at 60 mph, like turning a switch "on" at 67-68 mph (calibrated speedometer). Vibrations/harmonics did not change in character/intensity as speeds increased over 67-68, substantially reduced below that speed, undetectable below 60 during deceleration. Removal of front double cardan driveshaft = no vibrations at any speed. Installed new Tom Wood front driveshaft because center joint worn and chirping. Repeated tests - no change other than chirping being gone. Change in front pinion angle = bad vibration if front pinion angle lower than front driveshaft angle, gradually reduced as pinion angle matched to driveline angle and reduced slightly more with front pinon 1 degree higher than driveline angle. However, caster was reduced so much at that angle that steering was slow to return to center. The maximum I could adjust the front pinion angle was 1.5 degrees above driveline angle before lack of return to center became objectionable. Stopped experimenting at that point and addressed problem by converting to manual hubs. Issue resolved.
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Yes, I've been following his thread. If I remove the front ds, I still get the harmonic at 50-60mph. The 65+ vibe is reduced. Locking hubs would help, but not solve it completely. My tires may actually be contributing simply because they are worn out, cupped, and are basically 32's right now. I'm not going to do anything major until I get new shoes, then re-evaluate.
 
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JMT said:
What about some kind of rubber welting between the skid plate and the frame? I read somewhere about this possibility. Just a thought, though I'd say its nickel and dime thought
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I tried using 1/8" thick teflon washers to try changing the harmonic. Didn't help. I'm considering lowering the tc skid 1.5" to see what that will do. I'm also not ruling out the rear diff. I checked tooth pattern a while back and our resident gearhead @Rob5589 said they looked too deep. It likely is not one set thing, but maybe a series of clusters putting it over the edge. I can deal with the 50-60mph harmonic by turning up the stereo. the 65+ vibe not so much.
 
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Alex01 said:
I am watching wheeler dealers on my dvr and they started talking about harmonic vibrations. The new mechanic said they could be caused by the harmonic balancer on the crankshaft. Instantly I thought of your issue.

Figured it was worth passing on.

Also, I like the bottle opener. My mother in law gave me an old one her father used to use way back when a few weeks ago. I told her I was going to mount it on the bumper. I guess great minds think alike.
Click to expand...

I replaced my crankshaft damper and it did not make an iota of a difference. The one that was pulled out was in good shape per the shop (have just 58k miles on the vehicle but those do degrade over time so it was worth a try).

The two things that helped me were:

  1. 1/4" steel skidplate from UCF
  2. Lots of sound deadening in the tub +80 mil Noico did not help vibes, but putting another 170mil on top made quite a difference. I would have done it anyway just for thermal insulation and road noise)

I plan to install hardtop headliner soon.
 
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bobthetj03 said:
The latest round of TC skid swapping, and Tom Woods massaging of the front DS did net some improvement. Still have that lovely harmonic wave at 50-60mph. Then again at 65+. If I drive at 62-63mph it almost feels normal. Glad I have a good stereo. I can drown out a lot of it with some FFDP.
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Have you checked the torque spec on your motor mount bolts?

Are they overtightened?

Do you have good motor mounts?

The reason I ask is I just finished installing a Brown Dog 1" MML and the instructions were very specific about not tightening the main motor mount bolts too tight, because if too tight they would cause resonance and vibration due to the ears being pinched and making the mounts almost solid.

Do you have a good, not deteriorated transmission mount?

Read all 40 pages of your thread and just trying to think of simple, zero cost items to check.
 
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lindsey97 said:
Have you checked the torque spec on your motor mount bolts?

Are they overtightened?

Do you have good motor mounts?

The reason I ask is I just finished installing a Brown Dog 1" MML and the instructions were very specific about not tightening the main motor mount bolts too tight, because if too tight they would cause resonance and vibration due to the ears being pinched and making the mounts almost solid.

Do you have a good, not deteriorated transmission mount?

Read all 40 pages of your thread and just trying to think of simple, zero cost items to check.
Click to expand...

I have not touched the motor mount bolts, but I did have the mounts checked for wear by having one of my mechanics inspect the mounts for movement as I moved forward and reverse in 4lo with the brake on. I replaced the trany mount just to rule it out.

Here is a thread I started a while back that goes more into detail if you are bored. It's a long read.

https://wranglertjforum.com/threads/re-geared-now-i-have-a-vibration-above-50-mph.4235/
 
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