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Need Guidance on Noise

S

spinaldex

NAXJA Forum User
Location
Oregon City, OR
~2000-2400 RPMs, only when vehicle moving, strange raspy noise from rear of vehicle. Turns on under heavy throttle not light tap on pedal. Stops like clockwork at 2400 RPMs.

Took off driveshaft, put it in 4x4 and drove it, no problem.

New u-joints, still happens.

Pulled diff cover, drained, sprayed with brake cleaner, drained, new 80/90 3.5pts, still hear it.

Shook exhaust, kicked the tranny crossmember, suspension, etc nothing seems to move in the slightest.

Any clue what else it could be?

Thanks.
 
It almost sounds like a mix between an exhaust leak and metal scraping. Hard to explain.

I was worried it was something in the pinion, but everything looks incredibly clean in there. Not even the slightest metal shaving.

What kind of noise does an outer bearing make? Or, if there's anything failing in the drum, could it make a much louder noise at certain RPMS and would it happen regardless of engaging the breaks?

I don't think its exhaust, why would I hear something only when the vehicle is moving.

Maybe t-case chain? Drain and new fluids to see if its low? I picked up the vehicle this year so I can't say if it has enough in there.
 
Thinking this through more, if I remove the rear driveshaft, doesn't the entire rear axle assembly still spin? So, since the noise went away, doesn't that either mean its in the t-case since there's no load (ie chain), or its in the driveshaft?
 
Yes it still spins. If its gone without ds it means the problem is with your ds or tcase. I just replaced a stretched chain myself took forever to track down
 
Try pulling the rear DS and packing the splines with a heavy grease--Green Grease is my favorite--see if that helps.
 
I read somewhere that if you remove the rear driveshaft and try to twist the rear shaft on the t-case, if it moves a little that means there's slack on the chain. Is that true?
 
spinaldex said:
I read somewhere that if you remove the rear driveshaft and try to twist the rear shaft on the t-case, if it moves a little that means there's slack on the chain. Is that true?
Click to expand...

NO, NOT TRUE. There will always be gear lash in the drive train, also are we talking 5speed or auto? I can get about 10 degrees of rotation on my t-case rear output when my jeep is in 5th gear. The smaller the gear the less lash. In nuetral you can spin it all day long......

I would bet your problem is more of a pinion bearing issue or a wheel bearing but Joe peters suggestion is cheap and easy first. Also, when you are dragging your rear axle instead of applying torque through it you aren't really checking anything on it.......
 
Packed grease on the splines for the rear DS and the sound still happens.

Put it in 4-Hi and 4-Lo, sound still happens.

Drained and Filled T-case with fresh ATF, and sound still happens.

Sound always happens @ 2k RPM, regardless if I'm in 4-Lo, 4-High, or 2W drive.

When I stick my head out the window, it kind of sounds like its under my seat ... maybe not in the rear? Tough to tell.

I heard pinion bearings make a constant noise, like a whirring, not an intermittent noise at just a certain RPM. Is that true?

What else can I do to narrow this thing down?

Thanks guys!
 
Sound is hard to explain. Doesn't have a ring to it. More of a metal scrape, medium pitch, fast rate. Resonates from under the vehicle, can hear it out the window. Not very loud. My buddy couldn't even hear it since he doesn't have the best ears, but I picked it up easy. It also only shows up if I put the pedal down at least half way. If I slowly accelerate I can go right past 2k RPM and never hear it. So, more torque = more noise.

Also, sorry for not answering this before, ... this is an Automatic. Shifting is clean FYI, no issues whatsoever, so I wasn't thinking it had anything to do with the transmission. Was thinking farther back.

How can I test if its pinion bearing, wheel bearing, etc?
 
Oh, one last thing ... rig has less than 10k miles on the D35 with the Super 35 kit installed by the previous owner. The receipt shows they did a full kit with new bearings, seals, etc. Wouldn't they do the pinion bearing too? Owner only put street miles on it too, literally no wheeling. Well, he went once, got scared, sold the rig (haha). Could the bearing really go out that quick?!
 
I have had a mystery noise for 120k miles, replaced front hub bearings, rear wheel bearings, had all bearings & seals replaced & both axles set up, new drive shafts front& rear, new NOS transfer case, finally gave up on it and just drove it. No issues, no metal flake oil from the drive line, etc. oh well.
 
Looking at your sig line, you have 7.5" of lift? I assume you have a SYE and a double cardan style rear driveshaft, well at least hopefully you do.

If you remove the driveshaft and the noise goes away the first thing I would think about would be the driveshaft itself. How is the rear ujoint angle at the rear differential? Any play in the double cardan joint? What about the centering yoke in the double cardan? I have had noise and vibration issues associated with all of these things over the years.
 
Nope. No SYE yet. I was planning on doing the trick I read about here where you can buy a double cardan slip yoke for $90 and add it to the shaft to make it double cardan without having to do the hack and tap to add the yoke in a couple months.
I figured if there was an issue with the angle, the only issue would be blowing u-joints faster. So, I have less than 20 miles on a new set of u-joints in the rear shaft but the sound is identical to before I replaced the u-joints.
As for the angle, I'm at work, but I'll try to take a picture tonight when I get home. It doesn't seem that crazy .. I've had worse on other rigs =)
 
spinaldex said:
Nope. No SYE yet. I was planning on doing the trick I read about here where you can buy a double cardan slip yoke for $90 and add it to the shaft to make it double cardan without having to do the hack and tap to add the yoke in a couple months.
I figured if there was an issue with the angle, the only issue would be blowing u-joints faster. So, I have less than 20 miles on a new set of u-joints in the rear shaft but the sound is identical to before I replaced the u-joints.
As for the angle, I'm at work, but I'll try to take a picture tonight when I get home. It doesn't seem that crazy .. I've had worse on other rigs =)
Click to expand...

I just twisted the t-case output to the rear shaft with just a 3" lift. With your semi-radical lift a SYE should be on your list of priorities......
 
Rubicon 5.5 kit with long arms, 2'' pucks and extended shackles. That's considered radical? Huh.

We'll either way, either an SYE or double cardan shaft is planned. Still need to find this damn noise. Argggghhhhhh.
 
spinaldex said:
Rubicon 5.5 kit with long arms, 2'' pucks and extended shackles. That's considered radical? Huh.

We'll either way, either an SYE or double cardan shaft is planned. Still need to find this damn noise. Argggghhhhhh.
Click to expand...

Anthing above 4.5" you should have an SYE and double cardan driveshaft. Just get the SYE first. If the noise is still there look for it then.
 
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