Shuddering sound at 70mph

[AlgUSF]

So my Jeep has been through a bunch... I'm noticing that I get a shuddering sound when I decelerate at 70mph. I don't really feel anything mostly just hear a noise. If I back off the throttle slowly, no shudder.

I have the Mopar 2" lift which netted 3+ inches back in 2022.
I regeared my Jeep from 3.45 to 4.56 this year and have 4k mi on the regear added a truetrac to replace the factory LSD.
I had the 19A recall done on my Jeep back in september and they broke my factory transmission and replaced it in October.

I put 35's on my Jeep this week but the noise has been happening on the highway for a month or two.

When I regeared my rear axle I had .004" backlash and the noise didn't appear till months later. I changed the diff oil last week had a little metal dust on it, but not much. This is my first diff oil change since my 500mi break-in.

Any thoughts y'all on where to check? I rotated my driveshaft and there was some play in it consistent with my Tundra. My first thought is to open the diff and measure backlash with the tires off.


EDIT: I put the 35's on this week, not last week.

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[AlgUSF]

Here are my lash measurements as well as where the indicator is placed on the tooth.

 

[azwjowner]

Shuddering or a high pitched whine? I have the identical configuration - manual, regeared to 4.56, rear Truetrac. Mine always has had a high pitched whine since new when coasting down at 55+. Even after my regear, it never changed, so I think it's my housing.

Otherwise the usual culprit is pinion bearing preload being too light. But, again, that's not usually a "shuddering."

 

[AlgUSF]

Shuddering or a high pitched whine? I have the identical configuration - manual, regeared to 4.56, rear Truetrac. Mine always has had a high pitched whine since new when coasting down at 55+. Even after my regear, it never changed, so I think it's my housing.

Otherwise the usual culprit is pinion bearing preload being too light. But, again, that's not usually a "shuddering."

No it is a pronounced shuddering noise, low pitched. Only when I come off the accelerator quick, like doing a shift. I detect it through sound, it isn't like the cabin shakes. My PTR and PTTR were right in spec.

 

[azwjowner]

No it is a pronounced shuddering noise, low pitched. Only when I come off the accelerator quick, like doing a shift. I detect it through sound, it isn't like the cabin shakes. My PTR and PTTR were right in spec.

How long does the sound last? Could be the driveshaft somehow binding and loosening with the quick reversal of torque. We don't have u-joints from the factory, however, so not sure how much the rzeppa joint can do that.

 

[JLJeepGuy513]

that backlash was way too tight. Should have been around .006 - .008. The amount of metal on that plug is about normal after break-in though. what does your ring and pinion pattern look like? I think you will have long term issues with backlash that tight.

 

[Terrymo]

No it is a pronounced shuddering noise, low pitched. Only when I come off the accelerator quick, like doing a shift. I detect it through sound, it isn't like the cabin shakes. My PTR and PTTR were right in spec.

This might be worth watching. In the middle of the video, there is discussion about shudder occurring at high speeds when letting off the throttle. It may be worth giving the driveshaft another look.

 

[AlgUSF]

that backlash was way too tight. Should have been around .006 - .008. The amount of metal on that plug is about normal after break-in though. what does your ring and pinion pattern look like? I think you will have long term issues with backlash that tight.

The spec is .003-.006 from the Dana rebuild sheet.

 

[roaniecowpony]

From the Tech Authority (factory OEM) Service Manual.

 

[JLJeepGuy513]

The spec is .003-.006 from the Dana rebuild sheet.

depends if you used oem dana gears (2-cut) or aftermarket gears (5-cut). I assumed if you regeared, you used aftermarket? 5-cut will require a larger backlash.

 

[roaniecowpony]

depends if you used oem dana gears (2-cut) or aftermarket gears (5-cut). I assumed if you regeared, you used aftermarket? 5-cut will require a larger backlash.

I just learned something today. Thanks for that.

 

[AlgUSF]

I was thinking about the driveshaft, it’s been disconnected at least 4 times. Maybe something got damaged? On my OEM tires going from 3.45 to 4.56 means my driveshaft is spinning 33pct faster. At 70mph, the driveshaft is going like it would have a 92mph.

 

[roaniecowpony]

I was thinking about the driveshaft, it’s been disconnected at least 4 times. Maybe something got damaged? On my OEM tires going from 3.45 to 4.56 means my driveshaft is spinning 33pct faster. At 70mph, the driveshaft is going like it would have a 92mph.

Last August, I put a crease in my rear driveshaft on the Rubicon trail run. It also tweaked it just a hair. It vibrated on the drive back to Socal. But it wasn't noticable below about 50 mph. (4.88 gears)

 

[AlgUSF]

I'm thinking driveshaft after the discussions here, does the alignment of the driveshaft and yoke matter if the driveshaft is balanced?

I noticed that at the T-Case there is a mark on the flange and mark on the driveshaft.

However, I don't see any similar marks on the differential yoke and driveshaft. All I see are these two holes that aren't 180 apart.

When I did the regear, I marked with pencil and those marks are long gone.

Thanks!

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