mystery noise while coasting ( pls help )

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filly

filly

Joined
Jan 18, 2025
Threads
8
Messages
37
Location
San Clemente
Hi, I have been chasing a mystery noise while coasting for over a year now. At first, I had a gurgling noise from the front diff, and I replaced everything from the wheel bearings(haven’t replaced wheel bearings but those wouldn’t make that sound since they spin slower and the noise is coming from something that spins faster than my 38 in tires) to new birfs (I knew it wasn’t the issue, but they were clicking while turning), and new brass inserts that go in the spindle. That didn’t fix it, so I ignored it.

Three months later, I started on my 3-link build, so I also regeared. I took the front diff apart, and I was sure the noise was coming from there the pattern was really off, and my backlash was way off. So I put new gears in, got everything to spec, finished my 3-link, and got my stock driveshaft extended.

After that, I took it for a drive, and I hear this noise again.

The noise

So I get under the car, and the driveshaft angle is looking kind of steep. I’m thinking it’s the driveshaft, so I remove it and go for a drive and that loud noise is gone. But now I hear kind of a rubbing sound coming from the front (with no driveshaft).

I’m thinking it could be the non-broken-in gears, since they are brand new with a total of 2 miles on them. To be honest, I’m not really worried about that rubbing noise for now, because if it really is my front diff and I messed something up, I’ll just drive on it for now (since I was able to drive 4k miles on my really messed-up one) and just have Zuk take a look at it later and fix it.

But any ideas what that noise could be would be super helpful, since I’ve been chasing this problem for over a year now. I thought I fixed it, but clearly not.

Thank you in advance.
Also forgot to mention my car has more lift now with the 3link and my caster angle is higher and my axle is 2in more forward

Here is my front diff pattern
IMG_3752.webp


IMG_3751.webp
 
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Typically, a fast vibration (buzz) when coasting at highway speeds is caused by play in the slip yoke of a driveshaft. There should be ZERO rotational play in a slip yoke.
Any slop will cause the 2 halves of the shaft to "flog" around at speed with no load in either direction. Once load is applied (acceleration or deceleration) the vibration stops.
 
jonheld said:
Typically, a fast vibration (buzz) when coasting at highway speeds is caused by play in the slip yoke of a driveshaft. There should be ZERO rotational play in a slip yoke.
Any slop will cause the 2 halves of the shaft to "flog" around at speed with no load in either direction. Once load is applied (acceleration or deceleration) the vibration stops.
Click to expand...
The noise I showed in that yt vid was occurring at 15-20mph I assume it would be even worse at high way speed but I hadn’t been able to go on highway yet with the brand new gears
 
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filly said:
The noise I showed in that yt vid was occurring at 15-20mph I assume it would be even worse at high way speed but I hadn’t been able to go on highway yet with the brand new gears
Click to expand...
Remove and inspect driveshafts. Any rotational play in either the yoke or universals is bad.
Also check each universal for "notches" in either axis throughout the range of motion.
 
jonheld said:
Remove and inspect driveshafts. Any rotational play in either the yoke or universals is bad.
Also check each universal for "notches" in either axis throughout the range of motion.
Click to expand...
I just checked and there’s no play in anything but I am purchasing a double cardan shaft Tdy so I’m hoping that fixes it
 
You’ll need to make sure the diff flange points at the TC flange to run the DC shaft
 
Okay, I have replaced the driveshaft with a DC one and it still didn’t solve my issue; the noise is still there. However, I realized I have play up and down on my transfer case flange. It’s loose up and down. I wouldn't say it’s a lot of movement, but it’s enough to where, when I move the driveshaft up and down, I feel it. and when I put my finger on the t case flange and the casing I can feel it.

I also checked another 80 Series that doesn't have the noise issue, and there was also play in that flange. I would say it was a lot less than mine, but it still moved a little bit. Is a little bit of play normal? Should there be no play? Would there still be a noise if there is no front shaft with the center lock on? And if so, could that flange play cause my noise?

Also, I have by now replaced everything from the front all the way to the T-case (birfs, the brass spindle bushings, new needle bearings, new diff ring and pinion, and a new driveshaft). The noise is still there. The only things I never replaced are the wheel bearings and diff carrier bearings, but the noise sounds to be at driveshaft speed, and those bearings spin at wheel speed.

I previously thought the noise was the differential, so I took it apart and the pattern was off and the backlash was way off. I regeared it, it was my first ever regear—but the pattern was in spec and so was the backlash. So, I am going on here to ask if anyone has an idea what it could be.

thank you for help in advance
 
also it seems like with the dc driveshaft the noise is maybe a little bit quieter and l
CJF said:
At any point did you take a test drive with the front driveshaft removed? Might give you some helpful info...
Click to expand...
yes I did. the loud noise was gone but there was still a noise that sounded more like rubbing noise and it would also happen at the same times the one with the driveshaft installed would
 
You sure it’s not your brake(s), I.e a stuck caliper?
 
Idaho Savage said:
You sure it’s not your brake(s), I.e a stuck caliper?
Click to expand...
Im not sure about that, but how would that explain why the noise only happens when coasting (specifically when I am rolling down a hill and pressing the gas just a tiny bit or going up a hill fast and pressing of the gas)? Also, the noise changed when I took my driveshaft out. Initially, I thought it could be my brakes, since they had been lying outside in a shed for six months and the left caliper did get a bit stuck but, the noise is coming from the right side.
 
i had a person listen to the noise with me today, and it's coming from the front on the right side (if you had your feet on the floor sitting in the passenger seat, it's coming from my right foot's pinky toe). So, I don't think it's my transfer case, because I assume that noise would be more from the left side and right under my foot. Instead, I assume it's something in the differential, and I am wondering if it could be my carrier bearing. If you had carrier bearing issues in the past, where did you feel the sound from, and what did it sound like? and I would say the noise kind off sound like super knoby mud tires driving but louder.
 
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