Tracking down drivetrain or wheel bearing noise?

My 1999 XJ is noisier at speed than it's supposed to be. At about 35mph, you start hearing a low pitched howl that's not present in a normal Cherokee in good running condition. It just seems to get louder the faster you go up to about 55mph, where it then dies out a bit. At 68mph, it has a resonate howl that's louder than any other time. At speeds faster than 70mph, it almost diminishes. It's still louder than other jeeps though.

When I bought this thing in May I went through it and changed the front and rear gear oil. I'm using dino lube up front and synthetic in the rear. I pulled the plugs this weekend to see if they were still full and they were. The synthetic oil looks like new. The front oil has blackened already. I had sprayed the gears down with brake cleaner when I had the covers off, to inspect them, so the black is from the breakdown of the oil. I don't drive through water, and I haven't gone off road at all. I changed both the transmission and transfer case fluids with mercon III when I got it as well.


I also replaced the front axle u-joints when I got it and may have overtorqued the passenger wheel bearing when I was reinstalling stuff. I loosened it and put it back down to 175 ft/lb but I've never been sure if I messed up the bearing or not. The axles were clean and not worn up where they run on the seals in the pumpkin and they reinstalled smoothly, so I don't think I gauled either of the rubber seals. They're not leaking gear oil.

So trying to pin down where this noise is coming from, I've done some runs down the road where I swerve one way and then the other, looking for a change in the sound to see if the wheel bearing is bad. The sound does not change. I've also thrown it into neutral at speed when the noise is present and it doesn't go away just to rule out the transmission.

Is there any good way to isolate noise like this to figure out where it's coming from? I can't remember if the noise was present when I bought it or not, since I started doing preventative oil changing right away because the previous owner had not.

The tires on this thing are worn evenly, but it's time for new ones. They're Bridgestone duelers and they have had a long life. They're not on the wear bars, but they're old. I am pretty sure they couldn't cause this much noise, but maybe I shouldn't rule them out. But this noise is more mechanical like it's metal related.

Thanks for any help! The noise seems to slowly be getting louder, but I've driven about 2000 miles since I noticed it and it's not progressing fast enough that I've been able to point out where it's coming from. It's driving me nuts though!

Should I try a better gear oil in the front end? I'm using Napa's 75w90 stuff up there.

go to www.dodgeram.org/tech/repair/axle/diagnosis for some good TS tips.
Joe

That link says I'm forbidden to access that URL.

When I'm driving the jeep, I can feel the grinding through the gas pedal (the vibration of it.)

I'm new to 4x4 vehicles, so I'm looking for ideas of bearings that could wear out around 150k miles, which is what I have on the truck right now.

Other symptoms I can think of off of the top of my head are:
-It makes the same noise hot or cold. Doesn't get worse as the gear oils would heat up on the highway.
-It makes the same noise pulling or not. Engine engaged vs not engaged, the noise doesn't change.
-It'd be more of a roar than a whine. It's lower pitched than any gears I've had go bad in my RWD cars. It is also lower pitched than some wheel bearings I've had go bad.
-As weird as this sounds, the noise almost seemed quieter this past weekend when I was pulling a 1000# trailer at 75mph on the interstate than it does with no trailer at 35mph as I drove it to work today.

I found the page using this one: http://dodgeram.org/tech/repair/index.html

Thanks!

Mine does the same thing???? It's a '99 4x4 and I've had it since day one. The noise is now getting real loud. I keep cranking the radio up higher and higher. I've had every fluid changed. I can kinda feel some vibration in the steering wheel, but not much. Doesn't matter whether I'm under accelaration, coasting or braking. It's louder the faster I go.

I would love to find out what's causing this.

Probably front wheel bearings. Does it get louder the longer you drive? As they heat up?
150K is about a good time for them to go. Only other test is to remove front driveshaft to isolate it as a cause of the noise.

It doesn't get louder the longer I drive it as they heat up.

I did the hand test after a long highway drive and the passenger side is slightly warmer than the driver side hub. However, neither is too hot to touch or anything.

Think it could be related to the slip yoke off the back of the transfer case? Or possibly a failing U-joint in the rear drive shaft? Sounds a lot like drive shaft vibration (since it continues to spin at a rate directly proportional to road speed even if you've got the transmission in neutral).

you are supposed to use ATF+4 in the tranny and merconIII in the transfercase.

I wiggled the driveshafts around and they're not moving in the least. The u-joints appear to be taut. Out of balance could be a possibility though I guess. I need to do some silent tests with the engine turned off while coasting next I think.

Also, I need to have someone else drive while I ride elsewhere in the vehicle.

waylander said:

you are supposed to use ATF+4 in the tranny and merconIII in the transfercase.

Click to expand...

waking up a dead thread I know... but misinformation like this is really bad to have around. Do NOT use ATF+4 in an aw4, use dexron/mercon.

Hey, what a good time to wake the dead!

Yeah, I'm using Mercon III in my tranny and it is working fine.

Yesterday after MONTHS of this noise very slowly getting louder and louder, I made my best guess and bought a new front wheel hub assembly. It was impossible for me to pinpoint the noise other than "it sounded like it was on the passenger side and up front SOMEWHAT"

When you would bear right or left while driving the noise didn't change. Pitch didn't change. Shifting into neutral didn't change it. I was worried that it was a carrier bearing inside the differential going out.

Long story short, the right front wheel bearing was shot. I replaced it and the jeep is silent, like driving a car now. Even though the normal telltale signs of a wheel bearing (turning one way makes the noise louder or quieter) were not there, this is what was the problem.

As of noon yesterday I can live in peace while driving my Jeep again.

So as I said, the symptoms were a low pitched, non-directional rumble/howl. At first it used to resonate at like 35mph, 45mph, 55mph, 68mph as you sped up into those ranges or decelerated through them.

In the end, it just became a loud rumble at all times.

The old bearing in my hand is chunky and bound up. But it wasn't getting hot while driving on the highway....

So this mystery is now solved.