JoeOh

The past couple of months I've been hearing a howling "Ooooo" sound as I coast off the gas pedal from 55 mph to about 40 mph. Below that I can't hear it even with the windows down and the radio off.

I checked the fluid levels, they are all good. The trans was a pint low so I filled it back up to proper level. That seemed to do the trick for a few days, now the sound is back. The trans is still at the same fluid level.

Then I checked the U-joints, pinion bearings, and wheel bearings for play. No play in them at all.

The sound isn't groaning or metal on metal. It's just a constant Ooooo sound. When I press on the gas it quiets down. I really hear this sound going down a hill that has a good slope to it.

Gimmie the news while I brace for it....

dave1123

Check your ring and pinion for backlash. You may have a carrier bearing with excess wear. These are much easier to replace than pinion bearings. I believe your 95 has the D35c rear axle which uses needle roller wheel bearings. These could also be the problem.

I had the same howl in my WJ but with power on. Then a rear axle seal began to leak. I replaced BOTH bearings and seals and flushed out and inspected the diff. The planetary spider gears showed a little wear, but no more than expected for 147K. The wheel bearings showed no abnormal wear and we blew out the vent hose. I haven't heard the howl since. The bearings and seals cost me $65 and the 70W-140 Synthetic gear lube cost me $30. My bearings are the caged taper roller unit bearings.

Look for wear on the decell side of the ring gear. That can be caused by too much backlash.

JoeOh

Right now the howling sound isn't terribly loud, and is only really noticeable coasting downhill. If it is the rear axle bearings how much of a leeway of time do I have before they completely fail?

I'll be driving the jeep nice and easy until I get them replaced. What are the signs that they are about to cause my rear wheel to go flying off with the axle?

And yes, I will be replacing them ASAP when I get the money. I don't plan to be hobbling on these for weeks on end.

dave1123

USUALLY a bad rear wheel bearing will cause the axle seal to leak first, but that's not set in stone. I told you that my axle is silent now, but I have noticed it moaning a bit after a good 65 mph run, that is after it gets hot. Normal driving at 55 is not a problem. Once it cools down, it's quiet again. It seems to be better after I switched to 75W140 Synthetic gear lube which has a friction modifier in it, but there is obviously some wear in the pinion and carrier bearings, I would suspect.

I would like to tell you a story so you'll be aware of what can happen if rear axle service is not done properly. I had my 97 ZJ's transmission rebuilt by a local franchise store of a national chain that will remain nameless. The owner told me my rear pinion seal was leaking and asked if he should change it. I told him "Go ahead if you know what you're doing." Two days after getting the ZJ back, I took off for my brother's place about an hour and a half away on the highway. It was nice summer weather so I was running with the windows down and the radio playing. I began to notice a howling coming from the rear, so I got off the next exit about 1 minute later. Just as I slowed to about 40 mph, there was a loud BANG from the rear and a terrible grinding, crunching sound. When I stopped, the rear axle was smoking. I put it in 4WD and proceeded on the shoulder of the local highway to my brother's house where we pulled the rear shaft. The pinion bearings had exploded! The pinion would spin without touching the ring gear and could be moved up and down about 1/2 inch! I drove back to Syracuse on the front shaft (242 t-case).

Monday morning, I showed up at the shop and argued with the owner, the result of which he agreed to replace the ring, pinion, bearings and gears at no charge. Again, 2 days after the rebuild, it started whining. When I went back to the shop, it was closed permanently. I called the national chain and was told the transmission was garenteed but all other work was the responsibility of the store owner. After a search of records, I found the owner's address and sent him a registered letter. I got no response, so I asked my family lawyer what I should do. He said I could file a lawsuit in small claims court, but the chances of winning was small and it might cost me more than the repair. I decided to drive it until it blew, but a year later it was still whining but getting louder. I sold the Jeep for parts.

Moral of this story, don't do any service on the diff bearings or seals unless you're sure you know what you're doing!

JoeOh

Of course I have a trusted shop in mind. I've been taking my vehicles there for years. It's a small operation, not some franchise chain. The mechanics there will refer me elsewhere if they can't do the job themselves.

Just watching some YouTube videos on differential work alone tells me I won't mess with the carrier bearings or pinion shaft. Too much with setting the proper pre-load requires special measuring tools to ensure even wear.

If I had more experience, I'd MAYBE do the rear wheel bearings. But still that would include opening up the differential. dropping the retaining shaft, keeping the diff togeather, dropping the C-clip, yadda, yadda, yadda...

So I'll leave it to the pro's.

I'm just wondering what sounds will the bad bearings make before they go kablooey? other tell tale symptoms too?

dave1123

I am a toolmaker with almost 50 years experience in the trade. I still have all the tools necessary to do this work, but the actual hands-on experience is a little like witchcraft. Differentials are the most important part of any drivetrain. Getting the bearing preload right is the most important part of the work. With hypoid gears there are tremendous forces trying to make these gears separate when under power so the bearings take a lot of stress.

When I told you about my wheel bearings, I was just relating what happened to my Jeep. It may not be your problem at all. A bad wheel bearing will sound like a deep rumbling under any power setting or just when cornering. You can hear it best when rolling downhill with the engine shut off.

I think you should get your diff checked out by a competent rear axle man. You need to check out the gear backlash and any radial or lateral motion of the pinion. The wear pattern on the ring gear should be in the center of the tooth flank and be even across the length of the gear tooth.

The thing that amazed me was the size of the gears in the D35. They seems tiny for the stress imposed on them, especially for off-road driving. I haven't seen the D44 used in the V8 trucks yet, but I'm assuming they're more robust.

I guess I'm done rambling now. Good luck with your Jeep.