More vibrations

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m9199

VibraJeeper
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Jan 16, 2019
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Biloxi, MS
I'm hearing vibes at around 45-55 mph (actually higher, I found out today that I'm indicating about 12% off, but ignore that, I'll get that fixed), but the vibes only happen in 4th gear. (4 speed auto).

I've been getting around this by switching the O/D off until I'm at 60, but obviously that's not a solution, only a bandaid.

I should mention that the vibes are only under power, and I can best describe as a slow wub wub wub.

Edit: what are the best, worst, and most likely case scenarios?
 
The sounds you describe generally indicate resonance of some sort. It could be any number of things.
1. Is there a torsional damper on the driveshaft output (aka balancer)? Some TJs came with them.
2. Has the driveshaft been balanced?
3. Can you replicate the sound in 3rd gear with the torque converter locked at the same engine RPM?

Can you drop the rear driveshaft and drive around in 4WD to see if the noise persists? That will narrow down the possibilities. (Be sure to leave it in 4WD when you park so it doesn’t roll away. Make liberal use of the parking brake.)
 
m9199 said:
the vibes only happen in 4th gear. (4 speed auto).

I've been getting around this by switching the O/D off until I'm at 60, but obviously that's not a solution, only a bandaid.
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If this is true, the vibes go away when you drop into third gear then it has to be either engine vibrations or a transmission problem. It doesn't seem likely it is anything behind the transmission like driveshaft, axle or wheels. I'd check carefully to be sure you don't have contact between the tub and the exhaust or any other part of the engine. You might also check and see how your mounts are doing.
 
You mention gear specific. I’d ask if it is rpm specific next.

Get to the vibe. Note the engine rpm.

It could be all sorts of things obviously. vibes in an auto at a specific gear are pretty rare. Torque converter would be the likely vibration or shudder culprit but usually that’s at or near a shift point not after TC lockup.

Usually vibration are something in the driveline going that just gets amplified at a specific rpm or speed. Rpm based look at things input parts to make the Jeep move that spin based on rpm not speed. (Engine, clutch, transmission). Speed based first look at output items. driveshaft ujoints, wheels tires, bearings etc.
 
pagrey said:
If this is true, the vibes go away when you drop into third gear then it has to be either engine vibrations or a transmission problem. It doesn't seem likely it is anything behind the transmission like driveshaft, axle or wheels. I'd check carefully to be sure you don't have contact between the tub and the exhaust or any other part of the engine. You might also check and see how your mounts are doing.
Click to expand...
Agreed. My son had a vibration we thought was the transmission but ended up being an air filter housing that had moved and was just touching a brake line block transmitting vibrations to the pedals.
 
m9199 said:
I'm hearing vibes at around 45-55 mph (actually higher, I found out today that I'm indicating about 12% off, but ignore that, I'll get that fixed), but the vibes only happen in 4th gear. (4 speed auto).

I've been getting around this by switching the O/D off until I'm at 60, but obviously that's not a solution, only a bandaid.

I should mention that the vibes are only under power, and I can best describe as a slow wub wub wub.

Edit: what are the best, worst, and most likely case scenarios?
Click to expand...

Best: you remove the front driveshaft and it completely goes away. You install front locking hubs and live happily ever after.

Worst: you do everything you can and you cannot resolve the vibration and you want to push your TJ into a lake or a river nearby.

Most likely: You'll go crazy trying to find the source of the vibration and spend a lot of time and money.

Questions for you:

1. Is this a recent problem after you did some modification to the vehicle? Lift, regear, axle swap etc?
2. Have you checked and made sure your driveshafts, ujoints, pinion angle are all good and perfect?
 
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I was getting driveline at 50 mph in any gear, so I made a t case drop from longer bolts as a band aid until I can put in an SYE and DC drive shaft. In my test driving afterwards I didn't notice anything.
Fast forward a week and a half later to now. I noticed the vibes just yesterday driving 40 min to the recruiter.
Chris said:
Oh man... does the vibration sound like a sine wave with an up and down point to it?

@psrivats
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I'd say that's a good way to describe it.
 
What size suspension lift, what axle ratio, what transmission, and what size tires are you running? Your Profile only shows your engine size.
 
m9199 said:
I only dropped about 5/8" using washers because that's when the vibes stopped, but now they're back.
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A 5/8" tcase drop isn't quite enough but that's as much drop as the short factory metric bolts used after 2002 allow. I'd go for a full inch with longer bolts with washers stacked between the frame and plate. You'll need 1" longer replacement bolts and slightly more than a 1" stack of washers around each of the six bolts due to there being a recess in the plate the first washer drops into. Take one of the bolts with you to a well-stocked hardware store and find a match in the metric bolt section, it needs to be rated at 8.8 or 10.9 which is a strength rating. Or buy a tcase drop kit for a 2003-2006 which will have the right bolts and spacers. Those transfer case skidplate bolts have a tapered head so a kit, which would have the correct bolts, would be better than the non-tapered bolts you'd find in the hardware store.
 
So the vibration does not happen in third at 50MPH, but does in 4th at 50MPH, then at 60MPH in 4th the vibration is gone? If so that should rule out some of drive line gear like drive shafts, pinion angles since those parts are spinning at the same speed no matter what gear the jeep is in at 50MPH (or any speed). Are you lugging the engine, I know on my TJ with 33" and 3.73 auto before I corrected the speedometer for the 33"s it would not lug in OD, but after the speedometer was corrected it would shift into OD to soon (for the mass of the new un-sprung weight) and vibrate. Corrected it the same way you are doing, turn off the OD.

Still check to make sure everything is tight from the T-case drop first sicne loose bolts plus "lugging" engine can produce vibrations
 
Well, I just test drove on the highway and suburban roads. I used a sound spectrum analyzer to help listen for the sound and a GPS for more accurate speed measurements.

The vibrations only occurred at 60 MPH and at 1.5k rpm. (At what point is lugging occur?) When I forced it down 3rd and 2nd I heard nothing, and 1st wouldn't let me hold 1.5k rpm.

If I'm understanding correctly, that rules out anything behind the transmission, because those turn at the same rpm no matter the gear, correct? And since it's only in 4th gear, then it has something to do with the transmission?
 
86433
Well, I found a possible culprit.
The intake air box was held on by exactly one bolt. Another one was almost out of it's spot, and one was completely missing
 
m9199 said:
I'd say that's a good way to describe it.
Click to expand...

Oh man... if that is indeed what it is, good luck on solving it, seriously. @psrivats has been trying to solve this vibration for 6 months now with no luck, and he's thrown over 5k at it. @Mr. Bills was fortunate enough to solve it with manual locking front hubs. Of course that isn't cheap by any means.
 
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