70+mph groan...?

I've searched exhaustively here and other places and can't seem to figure this out. My XJ is a 99, 110k miles, daily driver, no lift, Aw4, 231.

This groan sounds a lot like bearing noise and it isn't noticeable below 68-70mph. Above 70, the sound increases exponentially - at 78-80mph, it's plain L.O.U.D. There is an ever-so-slightly noticeable high-frequency vibration that is very slight and only noticeable on smooth road. Otherwise, smooth as can be.

This has been around since I bought the jeep w/89k. All services have been done and I have recently done the following to eliminate potential areas.

1) AW4 filter and oil change
2) fr/rr differential service
3) 231 oil change
4) new tires, Toyo Open Country H/T

The tires ride beautifully and really quieted down the highway noise, yet made this high speed groan much more noticeable. When changing fluids, all the drive-shafts appeared to be sturdy and solid with no movement detected at the joints.

Could it be front unit bearings at 110k? This Jeep has lived an easy life - never wheeled and always serviced properly. When I purchased the Jeep, I replaced the PS Pump & lines, steering box and exhaust header. Everything else is stock.

thanks

it could certainly be wheel bearings, but i would also check for play in the front driveshaft splines, and play in the pinion bearings on both axles. also, your transfer case is supposed to be filled with transmission fluid, although i have been known to put gear oil in them to slow down leaks.
with all of this said, i would bet that you have some worn bearings in the rear axle. i had one with the same symptoms, and it turned out to be a worn wheel bearing (right rear). personally, if i were to change any bearing/race in the axle, i'd try to do all of them. they aren't expensive(excluding the front unit hub bearings), and most are pretty easy to change(Excluding the inner pinion and carrier bearings)
good luck!

Thanks for the reply. FWIW, I used dex/merc in the TC and tranny, I was just lazy and typed "oil" as a generic term.

When you say bearings in the rear axle, are you referring to bearings at the hub, or inside the diff?

mine were at the hub. you can tell more about which ones are worn by when it makes noise- like if you let off the gas, does it go away? i'm sure somebody on here knows more about that than me.

I get a different noise occasionally at 70+ mph. It's a warbling sound accompanied by flickering red and blue flashes. Sometimes I can just floor it and the noise fades away into the background. Usually it just gets louder until I have to pull over. It's an expensive repair when that happens. :rtm:

My guess would be the outer pinion bearing. Does is do it all the time above 70mph? Only when accelerating? Does it do it when you let off the gas and coast?

It's constant - on, or off the gas above 70mph. Pinion bearing, eh...? I guess I need to do some research and find a "how-to". That's one I'm not too familiar with.

If it's constant then I would lean more towards wheel bearings. The pinion bearing usually whines and groans only when accelerating and holding constant speed anywhere from 20mph on up to however fast you're brave enough to go. It will stop when you let off the gas and coast to a stop.

I would either say something seriously worn in the transfer case or wheel bearings. First step would be to replace the wheel bearings. There's nothing to it. Just make sure you pack them well.

lowrange2 said:

If it's constant then I would lean more towards wheel bearings. The pinion bearing usually whines and groans only when accelerating and holding constant speed anywhere from 20mph on up to however fast you're brave enough to go. It will stop when you let off the gas and coast to a stop.

I would either say something seriously worn in the transfer case or wheel bearings. First step would be to replace the wheel bearings. There's nothing to it. Just make sure you pack them well.

Click to expand...

So at 70+ mph on the highway, I let off the gas and dropped the tranny into neutral, groan is still there. It's really noisy above 70 and not really noticeable below that mark.

I'm going to drop the front driveshaft off today and see if I can pinpoint if it's the differential, or the wheel-bearings.

I have a hard time believing the TC is really worn with only 110k on the clock. It's never been wheeled, a daily-driver with stock tires, etc. Maintenance has been religious...:thumbup: Perhaps the front bearings are shot....that'd be an easy swap, I guess.

Yeah. Swaping the unit bearings is a piece of cake if you have the right hand tools.

13mm 12 point box end wrench
what socket fits the axle nut
18mm wrench for the brakes
and big rubber hammer

I've taken that assembly apart so many times I can do it in about 15 minutes. lol

and removing the front drive shaft isn't going to keep the diff from spinning. Unless you removed both drive shafts. Then nothing would spin...

Removed the front and went for a drive...u joints def need servicing, but still had the groan. Lifted the rear off the ground, removed tires, drums, etc, and those bearings spin free and smooth - no leaks either. I do have a fractional amount of side-to-side play in the axle, maybe 1/32nd - tiny amt.

Next...

mhopton said:

I do have a fractional amount of side-to-side play in the axle, maybe 1/32nd - tiny amt.

Click to expand...

Pretty normal for a c-clip axle, btw.

Bearings can look and feel good and still roar. Keep in mind that you don't hear the noise at 30mph.

Had similar issues years ago, turned out to be the unit bearings.

http://www.oreillyauto.com/site/c/s...year=1993&make=Jeep&model=Cherokee&vi=1180189

There ya go.

Well, those are for mine. 93. They'll work but ya might wanna look them up for you.

Yeah, unit bearings are where I believe I'm heading. The noise is there above 70 whether I'm on/off the gas, floating, neutral, etc, it's there. So it's not engine/tranny related. I eliminated the front driveshaft as a possibility, which leaves bearings.

Is there a way to test the pinion for smoothness?

Thanks for the link lowrange.

thechief86 said:

although i have been known to put gear oil in them to slow down leaks.

Click to expand...

Bad idea

PERIOD

Fix your leak instead.

Update:

I have since replaced all 5 u-joints in the fr/rr driveshafts along with rebuilding the cardan joint in the front d-shaft, so those items can be eliminated. They were the original u-joints and after 12 years, were dry and not far from failure. Although that wasn't the problem, it needed to be done.

In a little more focused testing at speeds > 75mph, I do notice that the groan *is* more noticeable when I'm on the gas vs. just floating. I've repeatedly tested this while paying close attention and you can here it almost on/off as you get into and out of the gas.

With that in mind, I think I can eliminate wheel bearings and begin to isolate down to either a pinion bearing, or something in the rear end.

Thoughts?

Pinion bearing. More specifically outer pinion bearing. You MIGHT be able to get away with just replacing that bearing and not reseting the gear set.

Either way you'll have to pull the carrier. You'll need a new pinion seal and bearing. I'd certainly check bearing preload. As long as you don't mess with the pinion depth or carrier bearings then you won't have to do a full set-up.