What's that noise?

Alright I'll do my best to describe it and pre - answer any questions

Noise coming from rear end area, but could be echoing. Haven't done thorough checking under there for the noise yet, just noticing while driving, it's very noticeable.

It's a whining noise, that can be heard starting around 20-30mph, ( it's probably there all the time but can't hear at lower freq) . It gets louder progressively with vehicle speeding up, and goes down in freq as vehicle slows down , so it's there acceleration and deceleration.

Here's the key thing I noticed: you know that moment you let go of accelerator, there's a second or so between release of accelerator and engine starting to slow down under compression. During that second, ( which is kinda like neutral? Maybe it is neutral) the noise is gone. Then it kicks in right away as truck decelerates, all the way until 20-30mph then you can't hear it anymore.

Diff and t case got drained and refilled recently with 80-90 Lucas dino as everyone recommends. Yes I have the LSD

Checked wheel bearing play recently in rear by pushing on tire up and down while jacked up, a slight play but very little

I'm thinking because it goes away during that brief second of " neutral" , that removes all items that are constantly rotating no matter the load, like tire road noise, wheel bearings , inside diff I'm not sure though...

Any ideas?

 

funny you mention this, I came to post a very similar issue. some questions for you

Brake pads are good?
Have you lifted a rear tire, put truck in neutral (WITH FRONT WHEELS CHOCKED), and spun that rear wheel?

My issue seems to be at the transfer case, where rear driveshaft meets it.

heres my truck with the noise from outside: https://youtube.com/shorts/6n9Yyh6CR28?feature=share
noise from inside truck: https://youtube.com/shorts/eOGz48IdjXU?feature=share
noise at transfer case while spinning driveshaft: https://youtu.be/tK0aAhxiMR8

 

Hmm interesting, I'll have to watch with headphones later. Checked rear brake pads yesterday, they aren't the best but they aren't scrap either, somewhere in between. Fronts are new. Ish, rotors too.

Yesterday I had both tires up, spun both by hand, even put it in drive and let it go up to about 2k rpm before braking, didn't really hear anything... may have to do a bit more thorough searching under there

 

mine only makes the noise after 10-15 minutes of driving. hows your rear diff breather look?

 

Hmm kk I'll check and see if mine does it right away or after 10-15 minutes.

Rear breather was gunked up but I recently freed it up. Still, could probably be switched out

No weeping at axle seals though, so pressure doesn't build enough to Leak there or anything

 

I think the fact that it goes away when there's that 1 second transition between acceleration and deceleration is key though, not sure how but key. Maybe today on highway I'll decelerate, put it in neutral while decelerating and see if it goes away. I feel like it will..

 

yeah i thought the same, until it started making the noise all the time. you could also check your dust shield, see if thats rubbing anything

 

For sure, easy one to check

 

Alright update on the noise!

It goes away when going into neutral, for example I'm coming off the highway, noise is whining, switch to neutral, it's gone.

Also, I tried around 60km/hr when letting go of gas , noise is whining as per normal. I switched to 4x4 while decelerating, it goes away immediately.

So, neutral and / or 4x4 makes it go away.... Thoughts? I was thinking transmission but now with the 4x4 thing I'm thinking maybe the ECGS bearing?

 

Do you mean the needle bearing? Or did you already install ECGS ? I doubt that's the sound of your noise. If the needle bearing goes out it will make a vibration that goes away when you put it in 4WD. Never heard of one making noise.

 

I meant needle bearing, pretty sure last owner didn't put in the ECGS bushing. I just finished watching a video of needle bearing VS bushing noise, guy setup a camera under the truck , definitely has a noise difference

Do you have any ideas based on what I identified?

 

I mean, the driveshaft should still be spinning when you're in neutral, and the gears in the pumpkin just the same. So I doubt it's something in the driveline or it wouldn't stop even when in neutral.

The only thing that's not really engaging when you're in neutral is ... the transmission. Totally unheard, I'm going to take the best bullshit potshot I can and say it's in there, torque converter. I mean, I suppose it could be planetary gear related, although I think most of the planetary gear stuff only really impacted the early-early models? I don't know much about the 5AT in our trucks. Maybe there's an output bearing, and that's shot? Whining, squealing, and wub-wub noises are often times bearings.

 

I had that thought as well, until I realized 4x4 made it go completely away, which anything 4x4 is post transmission... So if it was transmission, 4x4 wouldn't matter... Thoughts?

 

May be rear end too. In neutral the gears are unloaded.

Is the whining noise on decel lighter than when accelerating or vise versa?

 

No I'd say noise is same accel or decel

Neutral gears are unloaded for sure, but why would it go away in 4x4? Rear end would be same wether 4hi or 2wd no?

 

That's true. Forgot to to take that into account.

 

No worries, so yea maybe the needle bearing?

 

Finally watched the vids. The noise comes from the t-case when spun by hand?

If yes, probably a bearing or something inside it.

 

I havent tried that yet , can the tcase be spun by hand with wheels on ground?

 

Alright all, here's some research I did today. 2 videos, own taken right under rear diff, one taken looking at dash. This is with rear axle on jack stands , acceleration to 60kph and release.

For the dash video, notice the staggered slowing down , I know tires are in the air so it could act weird for that part, not sure though.

Thoughts?

https://drive.google.com/drive/folders/1ufuG4RrN3tOqwJhp7Ni0FKaLOC95J_b4

 

Is it from the diff and not the transmission/transfer case?

Sounds like the bearings are toast.

 

I'd say I'm 80% sure it's the rear diff now , especially after this last vid

 

What bearing do you think it could be @assassin10000 ? I'm guessing there's some bearing where shaft meets the diff?

 

There's 4 in the diff. 2 pinion bearings and 2 carrier bearings. Any or all could have issues.