Grinding/vibrating noise on deceleration? (1 Viewer)

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Mar 12, 2021
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Oregon
I know it’s going to be hard to diagnose this without hearing it but I thought I should ask on the forum before I get any crazy ideas. So on my 96, there’s an odd grinding/vibrating noise whenever I let go of the gas whenever I am above 25 mph. If I am cruising around under that, there’s no noise, or it’s so quiet I don’t even hear it. But during acceleration there’s no noise at all, it’s only on deceleration, any ideas?
 
I know it’s going to be hard to diagnose this without hearing it but I thought I should ask on the forum before I get any crazy ideas. So on my 96, there’s an odd grinding/vibrating noise whenever I let go of the gas whenever I am above 25 mph. If I am cruising around under that, there’s no noise, or it’s so quiet I don’t even hear it. But during acceleration there’s no noise at all, it’s only on deceleration, any ideas?
First place to look are the U-Joints.
 
Assuming you haven't lifted your truck recently it is worth pulling the driveshafts and giving them a little love and attention. Not complicated by any means but watch the orientation of each part of the shaft.
 
Assuming you haven't lifted your truck recently it is worth pulling the driveshafts and giving them a little love and attention. Not complicated by any means but watch the orientation of each part of the shaft.
Well I should have mentioned, when I bought the rig, it had a 3” lift already installed, could that be one of the issues?
 
They were still on the vehicle, I guess I could remove them and just get new ones since they’re not too expensive
I like to pull the driveshafts once a year for a full detailed inspection and lube. It's really the only way to see if there is wear in the UJ's and slipyoke.
 
Already checked those, they’re fine
So, you are unsure of the issue, yet as we present possibilities, they have been checked.

How about stating those things you know and have done, including modifications so that we may possibly approach the answer sooner than later, instead of playing the game of back and forth, making assumptions on what has or has not been done.


Then your transfer case bearings are shot. Remove and replace as necessary.

Maybe even possibly, it be your head gasket that has failed.
 
So, you are unsure of the issue, yet as we present possibilities, they have been checked.

How about stating those things you know and have done, including modifications so that we may possibly approach the answer sooner than later, instead of playing the game of back and forth, making assumptions on what has or has not been done.


Then your transfer case bearings are shot. Remove and replace as necessary.

Maybe even possibly, it be your head gasket that has failed.
Ok well there is a 3” lift, as mentioned above, and I have not done any other modifications to the vehicle, everything else is stock.
 
Ok well there is a 3” lift, as mentioned above, and I have not done any other modifications to the vehicle, everything else is stock.
Did you check your U-joints with the drive line unloaded?

and I do NOT mean on jack stands.
 
That is the ONLY way to determine if your U-joints are loose or have play.

Wheels chocked. Transmission in neutral. Engine off.

Then you grab the DS at each joint, attempt to move it up, down, left and right.
Then check for rotational play that is NOT gear lash.

Any movement up/down/left/right indicates worn u-joints.

I recommend greasing your DS u-joints and slip yokes to see if the noise goes away. You need to grease your DS with the driveline unloaded as well. That allows the grease to go where it needs instead of to the open spaces.
 
That is the ONLY way to determine if your U-joints are loose or have play.

Wheels chocked. Transmission in neutral. Engine off.

Then you grab the DS at each joint, attempt to move it up, down, left and right.
Then check for rotational play that is NOT gear lash.

Any movement up/down/left/right indicates worn u-joints.

I recommend greasing your DS u-joints and slip yokes to see if the noise goes away. You need to grease your DS with the driveline unloaded as well. That allows the grease to go where it needs instead of to the open spaces.
Could you explain a bit more what you mean by the driveline being unloaded? I'm about to give my prop shafts some attention, and I'm not as familiar with how to inspect them. Thanks.
 
Could you explain a bit more what you mean by the driveline being unloaded? I'm about to give my prop shafts some attention, and I'm not as familiar with how to inspect them. Thanks.
Look at the previous post.

I don't mean having the driveline hanging from a hoist or jack stands. It means to not have any rotational loads on the driveshafts. Having the wheels chocked, the transmission in neutral, removes the loads on the joints and yokes.
 
So the cruiser has been driving free from this noise and vibration for years and then suddenly, for no known or imagined reason, it’s growling at you on deceleration?

What do you know about the maintenance history of this 80? Do you know the details on you lift springs?
 
Don't even check the U joints, just replace them. I threw parts after the same sort of vibration, with a 4" or so lift, but never did my rear Ujoints because they felt fine. Learned to live with the noise/vibes. Rear joint finally felt bad a couple years later, so i replaced it, vibes gone instantly. With the lift you'll need new ones every 2 years anyway so get good at doing it.
 
I've had the same issue and it drives me insane. Lubricating shafts and U joints seems to quiet the vibration for a bit, then it goes back to gurgling/vibrating/grinding.

x2 on U joints--and while I'm at it, I'd recommend OEM (I did not, and I regret it, gonna have to do the same job over again now). They're a bit pricey, but allegedly (according to MUD) non-OEM joints tend to fail faster. Plus you get the warm and fuzzy feeling for installing parts of known quality.

Also, consider getting spares. Not sure how you use your truck, but a failed U joint on the trail or on the highway is a huge bummer and a potential recipe for disaster. Even if you replace them and they don't solve the problem (I genuinely hope they do, as I have the same thing), it's one pesky wear item off the list that you won't have to worry about for a bit.

There are threads on this, but ensure you replace in accordance with FSM to ensure the driveshaft phases are correct.

I'll save you a Google on the part numbers:
Front: 04371-60070 (x2)
Rear: 04371-60210 (x2)

Lastly, my truck's (babied by PO w/ no rust) driveshaft hardware was toast. You can get pretty new hardware from @NLXTACY at Wits' End, Solutions for Problems You Didn't Know You Had - https://absolute-wits-end.com

Sorry for the blast of info/suggestions. U joints are the bane of my existence.
 

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