Bad Hum/Whine in Driveline - Help?!
 

09 2dr auto with 3.73, 2.5" coil lift on 35's, just hit 40k miles

Getting a bad wine and hum somewhere in driveline only when giving gas and above 1500-ish RPM's. Hum stops the second I am completely off of the gas. Ran about 40mph down a hill in neutral giving gas and no hum. Please help me out guys. :dontknow2:

My first thought was rear drive shaft which is still stock. Can not see any grease or tear in cv boot. Shaft is always roatating even in neutral so that rules that out correct?

Second thought was gears but do not see any oil outside or around diffs - have yet to check oil level though. Again, gears are always rotating so if it was them the wine would be constant regardless of amount of gas and or being in neutral, correct?

Last thoughts and now worried that it may be something in the tcase or transmission. :sad2: ATF fluid looks good, doesn't smell burnt and doesn't feel gritty.

I have to imagine that I'm on the right track, but really could use some help on where to go and what to check next.

Sounds like a u joint is going out. I am assuming it is doing it in 2wd ? Crawl under your jeep and grab the drive shaft firmly one end at a time and shake it back and forth. Check for any loose play. Ujoints will usually hum/vibrate under a load first when they are beginning to fail. Easy fix tho.

Yes in 2wd - didn't think to check those.. I'll check them out, thanks for heads up!

Have adj rear lowers from RK's 2.5 max kit, but have been running them since summer with no issues on 33's. 35's just went on 2 weeks ago.

bit more for any of you that can help me track this down..

Whine definitely happens only under load and gas. Pitch of whine goes higher with speed/gas, not RPM's. Auto trans shifts fine all gears, no change in noise when shifting. At this point I have to assume its in the tcase, rear drive shaft or gears. Thoughts?

Bump for any more suggestions please?

Changed out rear diff fluid.
Tried to pull the rear drive shaft but could not break it free from the axle side. There was definite play there back and forth and I'm assuming there should not be any at all? This is the pinion nut and bearing?

Still there and loud, almost like a loud tire hum.
Trying to pinpoint origin but really hard to do that while driving. Going to keep her parked until I can figure this out or break down and just bring her to the shop...

:sad2:

If its when your accelerating that usually indicates worn ring and pinion or improper gear set up.
When you say back and forth, do you mean in and out at pinion or rotational. A small amount of rotational play is normal, in and out is not.

I think your reading to much into this. Do you still have the 33's. If you do try putting them back on. See if that makes a difference. You have a after market front shaft, drop that and see if that makes a difference, I have a small vibration on acceleration also but I know its the front shaft because I just blew the front shaft. and before I blew the shaft it was very smooth and then I got a new one and then the vibration started again. I say again because I had a tom woods on the front and had a vibration as soon as I put it on. After a little bit the front Tom Woods started knocking alot. So I replaced it with a tattons. The tattons had no vibration at all. Then I blew the tattons. (I was giving it hell when I blew it so I dont blame the company for the failure.) Well tattons sent me a new one and now the new one has a slight vibration when I accelerate. So I dont think its your gears. Honestly I think its just your new tires. But drop your front shaft and see if it makes a difference and it that doesn't work then drop your rear and see if that makes the difference. If either doesn't do anything then try to swap tires if you can. If that doesn't work then it could be gears but I dont think thats the case.

Meant in and out. Maybe about 1/16" or so.

Just ran both of those and did hit water. Noise is a bit lower pitched than that though and doesn't start until I'm moving. Will definitely check though.

Will check the pulleys this morning, just find it hard to believe that this noise would transfer to be that loud. Still stock gears. I can not for the life of me free up the ds from the axle. Got tcase side fine. Trying to pull from the axle is when I noticed the play in and out.

Think I got it!

Finally was able to get drive shaft out.

Threw it in 4hi around the block and loud hum is gone so it is definitely back there. Small bit of gear oil below diff coming from pinion seal. Since the seal is gone at this point I'd have to guess pinion bearing is the cause now for this hum?

Guess I mine as well just have this be the excuse to get the 5.13's.
Tough decision will be going for broke and putting the locker in while its all open... Thoughts?