SOLVED! Clunking from rear end

[Cdrum]

Hi all,

Original owner of a 2002 GMC Envoy 4.2 4-wheel drive with a G80 locker with about 120,000 miles on it. The past 6 months, I've been going through taking care of "deferred maintenance" so I can hand the keys over to my son who goes to school in upstate NY. One of the issues I've been dealing with is a clunking from what sounds like the rear axle area. Here's what I've done and where I am:

- Sound occurs mostly randomly - driving straight, turning, tends to do it more at low speed, and perhaps more during initial accel/decel.
- Originally I thought sway bar end links, the originals were shot and I replaced them. Sound persists.
- I could somewhat reproduce the sound pushing the either side tire in or out when jacked up. Almost like endplay on the axles and the spider gears - but very hard to isolate the nosie.
- I changed the rear diff fluid with synthetic 75w90 oil, which I believe had the LSD additives. The noise went almost completely away, but over the course of several days it started to come back -- then I noticed small puddles at the end of either axles of gear oil - leaking axle seals.
- Pull the rear diff-cover, pull the axles, replaced the bearings and seals. Refilled with new 75w90, through the breather tube. This time no leaks - BUT the clunk seems to be back, and it seems to worsen with the longer you drive (and the warmer the gear oil gets).

So before I surrender and take it to a shop, any ideas on what to try/test next? Maybe LSD additive package? Maybe the G80 is grabbing?

Thank you!

PS -- I used

Valvoline SynPower SAE 75W-90 Full Synthetic Gear Oil​

https://www.amazon.com/dp/B002HQGCVG/?tag=gmtnation-20

 

[TollKeeper]

You mention upstate New York, so I can only assume you are from the Rust Belt?

Anyways, there are 5 control arms for the rear axle. 2 on each side, and a lateral link. The 2 on each side are prone to rusting out, and sometimes the cup that holds them to the frame itself rusts out.

This is where I would start. The control arms themselves are pretty easy to replace, assuming you can get the bolts off.. The Control arm mount cups are usually a death sentence. They can be repaired, but only if there is enough frame to weld on the new cups.

Another thing to check, the spare tire. If the tire isnt completely on the hoist, and firmly set against the body/frame of the truck, it will rattle and clunk as you do any driving maneuvers.

 

[Cdrum]

TollKeeper - thank you for the quick response. The Envoy has lived its entire life in Maryland, so it hasn't yet experienced winter time NY. There is a bit of rust, but at this point it appears pretty superficial. While I was under I applied rust-reformer and underbody coating.

I will check out the trailing links and the lateral link --- and the spare tire, I think you might be onto something there!

 

[mrrsm]

Surprisingly.... The GM Eaton G-80 MLocker does NOT require any Anti-Slip Clutch Additive because unlike a Limited Slip Differential... it does NOT have any Friction Disks ...per se. (See the Documentation in the Link Below)

THIS Thread is chock full of additional Year Make and Model "On Topic" information that fell out of my own "Real Hands-On Experience" with partially re-building my own 2000 Chevrolet Silverado 1500 5.3L 2WD Rear G-80 MLocker Differential that may also prove its value to you from Post #27 onward regarding a focus on the errant use of Rear Differential Lubricant Additives inside of the GM Eaton G-80 Mlocker Differentials:

2000-2002 Silverado Rear Diff Partial Rebuild

Decided to use ACDelco Disks, Calipers and Ceramic Pads on the Front... and choose the AutoZone Duralast Top Quality Zinc Coated Rear Disks and HQ MAX Ceramic Pads. The New set of "Meaty" looking Parking Brake Shoes is from Raybestos, while the replacement PB Hardware Kit comes from ACDelco...

gmtnation.com

This is An Important Distinction Worth Mentioning...

"IF" your '02 Silverado sports a Leaf Spring Truck Bed Suspension vs. the Later Model Torsion Bar Style... those individual Leaf Spring Elements can Fracture; especially in Cold Weather with Rough Terrain Driving Conditions and then create those Loud Clunking Noise events you've described:

 

[Cdrum]

@mrrsm - thanks too for your response. I dread changing the gear oil again...though I'm certain when I last changed it I used Royal Purple 75w90, which had friction modifiers. This was probably 60,000 miles ago. I'll think on it - and I saw in the other thread recommended fluids that meet specs.

With respect to rear springs - this is air suspension, so two bags and compressor to keep them inflated. These were all replaced about 6 years ago, and in the time since its been mostly in the garage.

@TollKeeper - after your suggestion of checking the spare tire carrier, I cinched it up a bit (about a turn). Will do some test drives over the next couple of days. I may preemptively replace the trailing links and track bar too....

 

[mrrsm]

That leaves the possible issues of the Drive Shaft Rear Universal Joint Assembly Straps coming loose, Rusted Out U-Joint Needle Bearings ... or having an Incorrect Gear Lash between the Rear Diff Hypoid Gear Shaft, the inner Front Case-Bearings-Race and of course... The Ring Gear itself.

But... I would only suspect that area if I was hearing Low Frequency Humming or Thrumming Vibrations emanating throughout the vehicle at certain speeds created by certain Harmonics. It is RARE... but it can happen.

 

[Mooseman]

Another possibility is you need to grease the splines in the driveshaft slip yoke. I had this odd cli k coming to a stop and that fixed it.

 

[Cdrum]

@Mooseman - great idea, I'll check that too when I get back under tonight. Did you just use regular bearing or marine grease, or is there some special goo?

 

[Cdrum]

That leaves the possible issues of the Drive Shaft Rear Universal Joint Assembly Straps coming loose, Rusted Out U-Joint Needle Bearings ... or having an Incorrect Gear Lash between the Rear Diff Hypoid Gear Shaft, the inner Front Case-Bearings-Race and of course... The Ring Gear itself.

But... I would only suspect that area if I was hearing Low Frequency Humming or Thrumming Vibrations emanating throughout the vehicle at certain speeds created by certain Harmonics. It is RARE... but it can happen.

@mrrsm - fortunately, no thrumming that my ears can hear -- just the occasional fairly abrupt 'chunk'. Using Occam's Razor, I think it's likely one the things you all have already listed out. Here's my thinking:

-- Spare carrier - most likely
-- Slip-yoke splines - seems possible and maybe even probable as the clunks (I'm told by my son) increase the hotter the vehicle gets. Perhaps heat transfers enough from the diff to tighten slip yoke tolerance
-- trailing links or lateral link/panhard arm/trackbar (still trying to find a listing for that particular part). Of the links, my recollection is that it was the worst for wear, but not enough that I wanted to replace it.
-- Something else in diff - ring gear, etc - seems possible, but unlikely at this point

It's like a weird game of chance - what will it be? In all seriousness, thank you all for the great suggestions!

 

[Mooseman]

Did you just use regular bearing or marine grease, or is there some special goo?

Just regular grease. I used Lucas Red and Tacky, a good synthetic grease. I think any high temp grease will work. Mine were dry. I thought it was the rear shocks and unknowingly replaced them.

 

[TollKeeper]

Original owner of a 2002 GMC Envoy 4.2 4-wheel drive with a G80 locker with about 120,000 miles on it...

If your '02 Silverado sports a Leaf Spring Truck Bed Suspension....

You may be talking about 2 seperate things? Just making sure we are on the same page.

The other thing we have not talked about, have you checked the transfer case, and its fluid levels?

 

[Cdrum]

Had my son crawl under the Envoy today to look at the slip yoke - I think we're going to have to put it up on jack stands to lubricate, so it'll have to wait until this weekend.

@TollKeeper - yes, I think mrrsm was pointing me to the G80 rebuild that was applicable to other GM trucks. I'm definitely talking about a 2002 GMC Envoy with a G80 and air springs -- so no leaf springs to deal with.

I've not checked out the transfer case, though that's worth a look. I have serviced on schedule replacing the fluid at 50 & 100K miles. I will cycle through 4wd and 4wd low. My ears are telling me the sound is coming from further back.

Thanks again everyone - these are great leads to follow-up on. I'll keep you all posted!

 

[Cdrum]

UPDATE: May have found it

This morning I had the opportunity to put some miles on the Envoy with my father and his bionic hearing aids. Over the course of about 25 miles we determined the clunk occurred with higher frequency on left turns, typically on accel. Upon returning and parking, Dad rocked the Envoy while I listened -- we were able to reproduce it while I watched the suspension -- and bingo, found the sway bar end link on the driver's side was loose. I snugged it up and took it for another ride, this time shorter, but much quieter. I blame myself for not picking up on that earlier, and I need to thread locker both sides.

Not declaring victory yet -- that'll come when my son drives back and forth to summer school next week with his more youthful hearing.

I'll update next week with 🤞and hopefully good news.

Thank you all again for the amazing support!

 

[Cdrum]

Folks, declaring this problem SOLVED! Loose swaybar link on the driver's side - fix was to tighten and thread lock the ball joints --- did both sides. Incidently, both were accessible without needing to jack or remove tires.

Thank you to @mrrsm, @Mooseman and @TollKeeper - really appreciate the troubleshooting ideas.

 

[pell]

It always the simple things that are hard to find, a sketchy mechanic would have probably replaced the whole drive line, bill you and say " What noise" when you bring it back for the same problem.