Rattling when letting off the gas

ljrubiconma · Oct 23, 2020

Hey,

First post here. A little background: bought my ‘06 ljr in 2014. Has about 68k on the clock.. been using it as a summer/wheeling (hard) vehicle up until recently. Sold my more reasonable car (Honda pilot) in lieu of driving the Jeep everyday. It’s got the 4.0, 42rle, a 4” tera LCA lift, 35s, regeared to 5.13s, Currie Currectlynk, and a banks cat back.

Been chasing a weird rattle/grind that happens when I let off the gas for the past year and a half. It happens above 35mph and curiously enough goes away if I turn the OD off. It happens almost as soon as I get off the gas and lasts for about 5 seconds after.. it sort of sounds like something spinning but is definitely metal on metal.

So far I have:

Removed front DS (no change)
Replaced all control arm bushings
Replaced the tranny mount a couple years back
Replaced the rear axle shafts (the splines were wicked twisted)
Replaced the axle seals + wheel bearings
Replaced the rear sway bar bushings (links are shot though)
Replaced the front DS ujoint
Drained + refilled the tranny and tcase + replaced the filter
Readjusted the tcase linkage
Put on new brakes F/R ~ 5,000k ago
Readjusted the E-Brake

Possible culprits:

Pinion bearing/(no play in either yoke though..)
DS ujoints (front slip shaft is toast; rear doesn’t have play)
Tranny?? (Torque converter? No issues shifting/no shuddering..)
Tcase (input shafts???)
Exhaust (Lots of wiggle in the headers.. rear hangar also shot)

Just seems kinda weird that the noise goes away when I turn the OD off. I’d really appreciate some insight; this sound is driving me nuts.

Thanks!

PDoyle · Oct 26, 2020

Exhaust could be jiggling, could replace some rubber parts.

Kiwi_TJ · Oct 27, 2020

I had a similar issue with my Jeep. The block inside the cat converter broke loose and would rattle at the right engine frequency, usually just off idle or on overrun. I just got under the Jeep and started hitting stuff with my hand until I heard the same rattle, which in this case was the cat converter, once removed the noise was gone.

So you could remove or replace it and see if that fixes it.

DougRz · Oct 27, 2020

ljrubiconma said:
Just seems kinda weird that the noise goes away when I turn the OD off

Explain this better.

Does the noise stop if you're in OD and turn it off during? Does the noise never happen while not in OD? Can you induce the noise by going from not-OD to OD?

Since you replaced stuff front and aft, does that mean you can't locate whether the noise is front or rear?

2 quick things come to mind: the 42rle flex plate bolt issue, and the rear DS/pinion angle changing when letting off throttle. But the OD on/off variable is odd and neither makes sense given that.

ljrubiconma · Oct 27, 2020

Sure; the noise occurs when I'm in OD but when the OD disengage switch is turned on the noise goes away (or at least 95% of away). I think I have heard a similar noise with the OD off but its very rare and much quieter if its even the same noise. It is easy to induce if you are driving with the OD off and then reengage the OD; happens very predictably.

PDoyle · Oct 27, 2020

Think it could be rpm related?

BlaketheSnake · Oct 27, 2020

Take a borescope to the upper two catalytic converters...possibly the media is falling a part and will eventually clog up the third catalytic converter.

DougRz · Oct 28, 2020

ljrubiconma said:
It is easy to induce if you are driving with the OD off and then reengage the OD; happens very predictably.

Oh boy. Not good. Hopefully the change in vibration pattern as rpm changes causes something inside a cat as mentioned above. Otherwise the obvious is something internal to the trans.

Is it rpm dependent at all? And to what degree, linear or random?

ljrubiconma · Oct 28, 2020

DougRz said:
Oh boy. Not good. Hopefully the change in vibration pattern as rpm changes causes something inside a cat as mentioned above. Otherwise the obvious is something internal to the trans.

Is it rpm dependent at all? And to what degree, linear or random?

Quick update:

I got under the jeep to check the exhaust and it's wicked loose. The connection between the muffler and the tube from the muffler back is definitely loose/leaky.. Also after shaking the ***** out of the exhaust it seems like the noise is also there in OD/practically all the time.

Gonna get it to an exhaust shop and go from there I think. Tranny seems fine; shifts great and has been making this noise pre/post fluid and filter change.. will keep you updated once I get it to a shop.

DougRz · Oct 28, 2020

ljrubiconma said:
Quick update:

I got under the jeep to check the exhaust and it's wicked loose. The connection between the muffler and the tube from the muffler back is definitely loose/leaky.. Also after shaking the ***** out of the exhaust it seems like the noise is also there in OD/practically all the time.

Gonna get it to an exhaust shop and go from there I think. Tranny seems fine; shifts great and has been making this noise pre/post fluid and filter change.. will keep you updated once I get it to a shop.

Good news. Sounds indeed like OD changed the vibe pattern enough to make it rattle.

PDoyle · Oct 28, 2020

I want points for that.....:grin2:

ljrubiconma · Nov 17, 2020

So some bad news.. definitely not the exhaust.

Brought it to the shop and they replaced the hardware connecting the upper cats to the manifold, fixed a minor leak from the muffler back, and cut out the third rear cat entirely (kind of pi$$ed about that; long story short they were too lazy to check it the cat was bad or not and cut out the perfectly good cat without inspecting it instead.. getting that put back in tomorrow). Still making the same noise as it was before all of the exhaust work.

Not sure what tree to bark up next. Going to try replacing the rear dshaft ujoints to see if that helps.

WallyDog1 · Nov 18, 2020

ljrubiconma said:
So some bad news.. definitely not the exhaust.

Brought it to the shop and they replaced the hardware connecting the upper cats to the manifold, fixed a minor leak from the muffler back, and cut out the third rear cat entirely (kind of pi$$ed about that; long story short they were too lazy to check it the cat was bad or not and cut out the perfectly good cat without inspecting it instead.. getting that put back in tomorrow). Still making the same noise as it was before all of the exhaust work.

Not sure what tree to bark up next. Going to try replacing the rear dshaft ujoints to see if that helps.

It still sounds like a loose cat core to me. Not a fix for a bad cat but...I learned this devious hack years ago from the used car department when I worked at a car dealer in Boston. You can usually quiet a cat rattle by drilling a hole in the side of the cat and running a sheet metal screw into the hole. Check the depth of the outside to the cat core and pick a screw with the appropriate length. The screw holds pressure on the core and will last quite a while OR long enough for the 30 day used car warranty to expire. It will also determine if that's what's rattling if everything else fails.
Take it or leave it...

DougRz · Nov 18, 2020

Loose cat core definitely rattles.

I go back to the flex plate bolt issue, that's a known problem and is a rattle.

The rear DS, when letting off throttle, can momentarily make a noise. Not necessarily a rattle, but a noise.

WallyDog1 · Nov 19, 2020

DougRz said:
Loose cat core definitely rattles.

I go back to the flex plate bolt issue, that's a known problem and is a rattle.

The rear DS, when letting off throttle, can momentarily make a noise. Not necessarily a rattle, but a noise.

I agree with you... I can only relate to GM's of the 70's era, I know I'm dating myself! Loose converter bolts sound more like an engine knock. I'm still on the converter idea. If the converter broke apart he could have a chunk of the cat stuck somewhere else in the exhaust system too.

Rattling when letting off the gas

ljrubiconma

PDoyle

Kiwi_TJ

DougRz

ljrubiconma

PDoyle

BlaketheSnake

DougRz

ljrubiconma

DougRz

PDoyle

ljrubiconma

WallyDog1

DougRz

WallyDog1

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