This seems to be a common problem but I can't find a common answer.

2008 JK
3.5" Rough Country w/steering stabilizer
35"Nitto Trail Grapplers
A/T transmission

Jeep drove great, low noise, no vibrations. Even at 70-75mph everything was very smooth.

Then...I had my stock 3.73's replaced with 5.13's. They installed new bearings at the same time. Now I have a pulsing vibration that seems to move from front to back slightly. Someone described it in another thread as a "sine wave" and that seems accurate. I notice it around 40mph and up.

I had the tires balance and rotated because they were due and I thought the shop may have not torqued the lugs properly or something. No change.

Before I take it back to the shop I would like to arm myself with some good info. It seems a lot of people jump to the drive shafts as a problem due to them spinning faster. I guess that is possible but I had no vibration at 75 with stock and now a lot of vibration at 40-45 with the new gears. I think I would have noticed at least a small vibration at those highway speeds with the stock gears.

Could they have reinstalled one or both of the drive shafts improperly oriented?

What part of the gear install could have been messed up to cause a vibration like this?

At the same time they replaced the rubber portions of my transmission cooler line that were weeping, but I can't see that causing any problems unless I'm missing something.

 

Are you running stock drive shafts?

 

Disconnect the driveshaft on the differential side, rotate the driveshaft 180 degrees and re-install it. Do one at a time and see if it helps.

 

Yes, stock drive shafts

 

Good advice, I was wondering if they didn't reinstall them the same way they came off. I can try this tomorrow.

 

Thinking ahead here, if rotating one or both of the drive shafts does not fix the problem what are some possible mistakes that the shop could have made during the install?

 

Sounds like a drive line vibration, the shafts are turning more rpm now with the new gearing. I agree with the previous poster about rotating each shaft one at a time. If that doesn't work you may try removing the front shaft as a step of the trouble shooting process.

 

So I'm at the driveline shop having then rotate the front shaft 180 degrees at the front diff. I'll try it like that for a bit but they said they don't think the rear shaft can be rotated at the differential end due to the cv style shaft. Is that true or do they just not know?

 

So the shop rotated the front shaft for me. No change that I can detect. I'm dropping it off tomorrow so they can try different combinations of drive shaft orientations and test drive it themselves. For whatever reason I'm not optimistic. I spoke with a guy at Unlimited Offroad in Fenton, MI and he is leaning towards a bad gear install or cheap gears. The gears came through DTS, I think they are Superior brand.

 

I had 488 installed in the rear and got a light vibe around 45 or 50 and stops about 55 or so. Shop said its the drive shaft, but I didn't buy it. Needless to say the shop isn't and didn't fix it. Said I may have hit something off road, but hadn't been off road since the install. After looking closer and taking apart the rear shaft and regressing it, I think it's the pinion flange. No vibes with the rear shaft out of it driving with the front. Didn't happen prior to the gears. I think the shop was happy with an impact wrench or something who knows. I do notice my pinion flange on the rear axle looks a little out of round, like its either warped or when the shop re installed it to set the pinion somehow it's a little off. No oil is leaking, and it doesn't make any noise. 3 shops have looked at it and don't think it's anything to worry about, although one said I have a u joint going out in the rear shaft- stock, rear shaft. Another shop said it feels like like the drive shaft, but the stock shaft shouldn't create that vibe. Said it could be the crush sleeve not installed correct, and then said it would be expensive to check it and to just drive it. And if I had problems come see them and they could reset the gears but that I may never notice any issue beyond what I notice now.
Btw, bought the front axle already geared and does fine in 4wd. I'm clueless but don't want to keep chasing my tail.