Vibration/Rumbling only in 4x4 Mode After Lift – Need Advice

[alexlab79]

Hello everyone, I’m experiencing a rumbling/vibration issue on my Gladiator that I didn’t have last winter. Let me explain:

Last year, in snowy conditions, I often drove at 90–110 km/h in 4x4 without any strange noises or vibrations. This summer, I lifted the Jeep (2.5" front, 1.5" rear{spring and shock}), installed an adjustable front track bar, front link kit, added Mopar front LCAs to increase caster, and later added front Rancho brackets for better handling. Everything was driving fine after those mods.

Recently, before swapping to my winter tires, I got caught in a snowstorm and switched into 4x4 to get home. At speeds above ~85 km/h, I started noticing a moderate vibration/rumbling. At first, I thought it was due to my larger tires, but after installing my winter tires, the issue is still there. Once I go past 85–90 km/h in 4x4, I get this vibration. It’s not extreme, but definitely not normal.

I’d appreciate some input on possible causes:

• Could the differential angle be too steep due to the brackets + LCAs?
• Incorrect toe-in alignment?
• Bad bearing somewhere?
• Damaged differential?

For context, it’s a 2023 Gladiator with only 20,000 km.

Thanks in advance for any advice!

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[DanJT]

Did you by chance lower your driveshaft? I had the same lift and similar vibration, a 1" DS
Carrier bearing drop bracket solved the problem.

 

[alexlab79]

Did you by chance lower your driveshaft? I had the same lift and similar vibration, a 1" DS
Carrier bearing drop bracket solved the problem.

I have a custom 5/8-inch carrier bearing drop bracket, but that bracket is for the rear driveshaft, not the front. Can you explain a bit more? I’m slow to understand at first, but once I get it, I really get it. :P

 

[DanJT]

If you have the drop carrier bracket in the rear you should be good..
As for the front, you will need to have the caster set right, can't remember the angle of the top of my head (darn pain meds) but I believe you need the pinion angle somewhere between 5-7 Degrees. I have mine at 6. Degrees and no vibrations.

 

[Stan H]

If you have the drop carrier bracket in the rear you should be good..
As for the front, you will need to have the caster set right, can't remember the angle of the top of my head (darn pain meds) but I believe you need the pinion angle somewhere between 5-7 Degrees. I have mine at 6. Degrees and no vibrations.

6° degrees is factory caster , factory camber bushings in top of the knuckle are 0.25 from factory .

 

[alexlab79]

Update, issue resolved

Just wanted to follow up in case it helps others. The vibration was caused by the front pinion angle being too steep, a result of combining Mopar lower control arms with the Rancho correction brackets. That setup pushed the caster too far and negatively affected the front driveshaft angle in 4x4.

I went back to the stock LCAs and kept the Rancho brackets in place. That brought the geometry back into a better range, and the vibration disappeared.

While I was at it, I also adjusted the toe-in. It was around 1/4 inch, which was too much. I brought it down to somewhere between 1/16 and 1/8 inch, and the steering feels noticeably more stable now.

Tested it in 4x4 on Snow at highway speeds, everything is smooth again.

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