The '99 XJ I just bought came with Hercules Terra Trac 235/75/15's. They are very noisy. The noise picks up starting at about 25-30 mph and just gets louder. Anyone else run these tires?

I'm 99% sure (ok, maybe 90% sure...) it's the tires and not hubs or anything. I jacked up both sides and spun the wheels individually and can't hear or feel any grittyness, clicking, etc. so I don't think it's a hub. Plus, it comes from all around, not just one side.

These are the noisiest tires I've ever had, so I just want to get other people's opinions if they run these tires.

Thanks,

Emrah

 

I have the same tires and they are quiet, Sam size too.

I thinks it's either your front or rear gears or a pinion bearing.

When do you hear the hum? While accelerating or with your foot off the accelerator.

Does it start out quiet and get louder the longer you drive and the warmer the Jeep gets?

 

I see you said it keeps getting louder the faster you go above 25. That tells me it hums while accelerating. I think it's your pinion bearing man.

 

How would I check that?

Emrah

 

There are a couple threads about it that go into more detail if you do a Google search.

But generally, I think you want to have the tires of the end you are checking in the air and try and wiggle and feel movement where the driveshaft goes into the differential. Your pinion bearing is at the end of the driveshaft inside the diff.

It is a cone shaped gear.

You could look in this area and see if there is fluid leaking out. If so, that would mean the pinion seal is shot and is leaking gear oil through it.

 

Oh, I should clarify: It starts low speed and gets louder. It does it on or off the gas. I really didn't pay attention whether it quiets down after a while. One of those things where you get used to it and tune it out, so you don't notice if the pitch changes.

If it's the pinion bearing, is it something that can be pressed in/out easily or does the whole diff need to come out?

Emrah

 

It's a PIA and not something for a DIY'er from what I've read.

I have kinda the same issue. If you replace it the gears have to be re-gapped. I think most of gear assembly has to come apart. Could be wrong though.

I don't think its a cheap job either.

I think mine is the pinion bearing in the front of the transfer case.

If it does it on or off the gas, it may actually be the gears themselves. You can pull the covers and check the wear on those.

You could even luck out and see that the gear oil is low and add some and it take care of it.

 

If the noise changes based on the road surface- ie: different on asphalt than on concrete- it's the tires. If the noise stays the same it's probably something else.

 

Ok. Changed out diff fluid at lunch. Didn't look too bad. Noise is still there. I shook front driveshaft and felt some lash but I don't know how much is normal for the dana 30 rev cut diff. I could not discern any up and down or side to side slop in the yoke. Whar should ut "feel" like for lash at the yoke?

Emrah

 

It shouldn't move in/out or sided to side. It will rotate about the shaft axis a bit. Did you check the rear?

Is the movement in the u-joint?

 

There is no side to side movement. I could not detect and in/out movement, but I really couldn't judge it as the front driveshaft was still installed. There was "twist" slop though. When I had the cover off, I turned the shaft and could detect some backlash slop, some slop in the spider/side gears, etc. Nothing huge. The oil looked ok. Nothing spectacular, but not mud and sludge either.

The rear is solid. No slop whatsoever. I'm just not sure if the slop is supposed to be different. I guess I never checked on my old '97.

So it MAY not be pinion bearings. I dunno. The noise is constant, on throttle or off. Same. It's just a dull, annoying noise. Not grinding. Sounds pretty much the same as if you're driving down a hard packed dirt road; that's the sound.

And I did try actually driving on a dirt road, but again, it sounds like a dirt road, so I couldn't hear the pitch difference between the car and the dirt road. So much for that experiment.

So what exactly IS a bad pinion bearing supposed to sound like? High pitch? Grinding? People say you hear it on the throttle, but not off the throttle. Mine you hear all the time.

Any more suggestions?

Emrah