98 TJ rear end noise identification

B

Baldy91

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Joined
Nov 8, 2018
Messages
40
Location
Meridian, Idaho
Hey all. Been searching like crazy trying to track down a noise on my 98 TJ, 4.0, 5 speed, Dana 35 rear, 62k miles. Lifted 2.5" currently with no TC drop nor SYE, but no vibrations as far as I can tell.

The sound I'm experiencing starts to become noticeable when accelerating past 20-25 mph, and continues to increase in frequency as I go faster. It's almost a rhythmic "whirl" or scraping sound that is consistent. It appears to be worse when accelerating or at steady speed above 20-30 mph, but is also still present when coasting to a stop...but the frequency of the noise decreases (not necessarily the intensity). I've read many threads and listened to others videos on angry sparrows and loud rear pinion bearings, but this seems different. Here's what I've tried or so far:

-swapped wheels/tires, no change.
-disconnected front drive shaft, no change.
-sprayed WD-40 at all u joints on driveshafts with no change (just to see if it made a difference lol)
-braking doesn't change sound
-rear yoke seems tight enough
-front and rear diff fluids changed

I'll try to take a video later for the sound, but I'm confused because it doesn't seem consistent with what I've read on the forums. Disconnecting the front DS should have eliminated the front end as the issue, right? Aside from possible wheel bearings I guess...but sound appears to be coming from the rear?

What other things should I be looking for? If my driveline angle is off, could it cause such a sound? Maybe I should try dropping the TC 1/2"-1"?

Thanks!
 
Thanks, guys. I can just disconnect at the TC and at the rear diff similar to how the front came off, correct? I'll start there and try to get a short video uploaded from the cab, assuming the sound can be heard.
 
Baldy91 said:
Thanks, guys. I can just disconnect at the TC and at the rear diff similar to how the front came off, correct? I'll start there and try to get a short video uploaded from the cab, assuming the sound can be heard.
Click to expand...

Yes, and shift to 4 HI
 
Link to video:

I was going about 35-40 in this. Sorry for the shot of the carpets lol. Notice the "wah, wah, wah" type sound?

Next up, drive with rear driveshaft off. Hoping for something to point me in the right direction!
 
Double check the ujoints on the rear shaft. Lower the skid 1/2" with washers and repeat. Keep dropping a 1/4" at a time till it smooths out.
 
bobthetj03 said:
Double check the ujoints on the rear shaft. Lower the skid 1/2" with washers and repeat. Keep dropping a 1/4" at a time till it smooths out.
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U joints seem fine to me. I lowered about 1/2" to begin with and it didn't seem to make a difference.

I'll try driving without the rear driveshaft this weekend. I am hoping it's nothing major, or that I can address it before it turns into something major.
 
UPDATE:

Color me confused. Ran without the rear DS with absolutely no change in the sound. Does that essentially rule out rear end?

The sound, if you can't tell from the video, is lower in pitch and almost appears to have a rotational component. I swear it sounded like it was coming from the rear, but now I'm second guessing myself. Having run it without the front and now rear DS, what are my options left? I played around with rear brakes in case something was rubbing, but that didn't seem to change anything either. I guess wheel bearing could still be in play? Hmmmmm.
 
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Is it throttle sensitive ? As in changes as you accelerate or let off?

And no , the rear end isn't out of play unless it isn't turning .
 
AndyG said:
Is it throttle sensitive ? As in changes as you accelerate or let off?

And no , the rear end isn't out of play unless it isn't turning .
Click to expand...

It seems slightly more noticeable at cruising speed/steady throttle, but still apparent if I shift to neutral and coast (to a lesser degree).
 
Could be the front output bearing in the transfer case .

I put my rear wheels on a stand and isolated my pinion noise . Be careful though ....if it drops it's gonna be bad.
 
AndyG said:
Could be the front output bearing in the transfer case .

I put my rear wheels on a stand and isolated my pinion noise . Be careful though ....if it drops it's gonna be bad.
Click to expand...

Would that still be apparent with the front DS disconnected? Sorry for the ignorance! I've been thinking I may need to put it on stands to trace it appropriately, but that scares me too lol.
 
Baldy91 said:
Would that still be apparent with the front DS disconnected? Sorry for the ignorance! I've been thinking I may need to put it on stands to trace it appropriately, but that scares me too lol.
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Good point ..that would rule that out ..no front shaft takes the transfer case out of play.

Could also be a wheel bearing .

I'
 
Brakes would be next, also run on jack stands, then pull each drive shaft and then use your hand to roll the wheels back and forth and feel for any roughness, just try to eliminate one component at a time.
 
astjp2 said:
Brakes would be next, also run on jack stands, then pull each drive shaft and then use your hand to roll the wheels back and forth and feel for any roughness, just try to eliminate one component at a time.
Click to expand...

Yeah I loosened the rear brakes and rotated the rear tires up on jack stands by hand, and honestly couldn't isolate any dragging, grinding, etc. I tried the fronts back when I had the front DS off, but don't recall noticing anything out of the ordinary.

I noticed that the same sound is actually still there when slowing to a stop, but seems to correspond to a certain revolution spot...Much like a wheel that is out of true on a bicycle that rubs the brakes as it makes its revolution. I know wheel bearings can make that same noise, so can't rule that out. Tips on checking the front brakes or what to look for?
 
Pull the axle shaft on the rear first, Inspect, if not that then I would look at your unit bearings next. Inspect them, turn them by hand, I hate throwing parts at a problem...and not knowing what is actually wrong so just take it apart and look before you just change things. Its hard to troubleshoot by the web. Good luck
 
Update: Found a wide road where I could do a little swerving at speed...seemed like the driver's side was a little noisier when under load. Decided to jack up the front and check brakes. Lots of drag when turning the wheels by hand, especially over a certain spot on the driver's side. Tried bleeding brakes. Pulled off the calipers to inspect them, and gosh darn the driver's side just seemed frozen. I couldn't get the darn thing compressed.

So, one day shipping for a new remanufactured caliper from Amazon. Going to install tomorrow (time permitting) to see if that makes a difference.
 
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