mountainmanjoe

is that rust inside from water contamination?

tsoleno

I didn't see any rust. There is a rust colored mark in the pic. It looks like an inspection mark. No water in the oil either time.

Gumby22

Maybe it’s just the lighting but it looks like there may be chipped teeth on the drive gear for the locker.

Did you also put limited slip additive in with the new fluid? It doesn’t matter if it’s a GM/AC delco fluid, it still needs a friction modifier.

mountainmanjoe

my 2013 manual doesn't specify any additive.
His 2008 manual doesn't specify it.
Neither did my 2000 Astro with Gov-loc
I didn't put any additive in either, and they worked fine.
What does the friction modifier do?

tsoleno

This is what I found on the friction modifiers. Lucas said too that theirs didn't need it. Seems to be a moving target. I'll look closer into the gears. I thought if this gave me more issues, I'd talk to the gear shop that had done work for me before. But a long time ago and a different truck. #PIP4054D: Eaton Locking Differential Chatter Shudder Noise On Turns - (Jul 19, 2010)


Subject: Eaton Locking Differential Chatter Shudder Noise on Turns


Models: 2004-2007 Buick Rainier

2000-2011 Cadillac Escalade, ESV, EXT

2002-2011 Chevrolet Avalanche

2004-2011 Chevrolet Colorado

2003-2009 Chevrolet Express

2000-2011 Chevrolet Suburban, Tahoe

2000-2007 Chevrolet Silverado Classic

2007-2011 Chevrolet Silverado

2002-2009 Chevrolet Trailblazer

2004-2011 GMC Canyon

2002-2009 GMC Envoy

2000-2011 GMC Yukon, Yukon Denali, Yukon XL

2000-2007 GMC Sierra Classic

2007-2011 GMC Sierra

2003-2011 GMC Savana

Equipped With a Locking Rear Differential RPO G80

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This PI was superseded to update model years. Please discard PIP4054C.
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The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:
Customers may comment on a chatter or shudder from the rear axle on vehicles equipped with an Eaton locking differential. This condition would be noticed in parking lot maneuvers, turning, or during locking differential engagement and may be more noticeable when the differential is hot. Locking differential clutch chatter may be causing this concern.

Notice: This does not apply to vehicles equipped with RPO QS4 (Quadrasteer) which is part of option package NYS. Quadrasteer vehicles use Dana axles and have a different fluid requirement.

Notice: This PI does not apply to vehicles equipped with a RPO G86 limited slip differential.

Recommendation/Instructions:
If differential clutch chatter is encountered in a vehicle equipped with an Eaton locking differential, flush, drain and refill the differential with new synthetic fluid, use the fluid part number listed in SI for the vehicle currently being worked on. If the condition returns, replace the rear differential clutch plates and refill the differential with new synthetic fluid, use the fluid part number listed in SI for the vehicle currently being worked on. Refer to eSI for clutch plate replacement and set up procedures.

Notice: Eaton locking differentials used in 10.5 rear axles are equipped with steel clutch plates. It is a design characteristic of these steel clutch plates to exhibit more clutch chatter than other models.

Important: Installing any friction modifier causes the clutch pack in the locking differential to slip and miss engagement. A fluid flush can often remove debris that is a contributor to clutch chatter. Adding friction modifier additive can cause a loss of locking differential functionality.

Notice: On Quadrasteer equipped vehicles, simply flush the rear axle and refill with the fluid listed in SI document 793720 under the steerable application.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

mountainmanjoe

I've never experienced chatter or shudder from the rear axle

tsoleno

Gumby may be right on , what might be called the governor gear having some kind of defect. I looked real close at the little stem gear of the locker and at that gear, but that pic looks questionable. I could see that causing the problem it was having. Maybe the fine metallic powder on the fill plug. I'm guessing that it is serviced w/ the assembly . Which would then pose the question, do I have an improved version installed or try a used assy, or have oem parts put in it.

Gumby22

Perhaps I shouldn’t have been so concrete in my statement. I could be mistaken about it needing additive, but the experience I’ve had in both repair and replacement of limited slip diffs (henceforth referred to as LSD for ease of typing and its invitation to mind altering experiences ) have shown me that in some cases it’s necessary and in all cases it doesn’t hurt anything to add it.

For starters, the whole point of a friction modifier in a LSD is to eliminate chatter. Chatter is a result of the clutches repeatedly engaging and disengaging due to lack of lubrication. Several factors can contribute to this but primarily it’s caused by the oil not doing it’s job to begin with - providing lubrication to the clutch packs. Most often the cause of this is the oil level getting low due to leaks which causes the diff to overheat, leading the oil to break down. One other contributor I’ve seen is excessive water contamination due to a flood, off roading, or submersion while on a boat ramp.

Now consider that the clutch in a LSD operates on the same principles as a clutch for a manual transmission. If you repeatedly press the clutch pedal just enough to disengage it and then immediately release the pedal, what’s going to happen? You’ll probably get whiplash, but you’ll also cause uneven wear on the clutch disc, which will lead to erratic clutch operation - you may even notice it feels like the clutch is engaging and disengaging on its own - aka chatter.

In terms of LSD operation, there will ALWAYS be a given amount of slip in the clutches during cornering/turning maneuvers when the difference in wheel speed, side to side, is great enough to cause typical differential operation. In other words, the LSD is functioning just like a standard open diff, but the clutches are slipping without engaging. This is totally normal and not a problem as long as the oil is doing its job.

But, if chatter has been diagnosed as the root cause of a noise or drive ability concern, what then?

According to the T-S-B-S you found, you should just drain and refill the fluid, and if that doesn’t work, then replace the clutches. Well, I don’t know for sure, but I’m guessing at a dealership, to have the fluid replaced once and then the clutches after that would be upwards of $1000 in parts, fluid, and labor. Most people would be less than thrilled to have to spend that much money on any vehicle repair, let alone when they were told at the first visit that replacing the fluid “might” fix it.

The problem with the recommendation in that TSB is 2 fold:

1) Simply draining and refilling the fluid does nothing to address the uneven wear in the clutches. They will not smooth themselves out back to even thicknesses just because there’s new fluid.

2) The recommendation to avoid LSD additive is GM’s way of telling their employees to cover their ***. They can’t recommend additive as a fix for chatter for the simple reason that if the problem is severe enough, additive isn’t going to help anything; but as soon as someone leaves the dealership and gets in a wreck because they recommended additive for a problem it couldn’t fix, the lawsuits start lining up.

You may have noticed the statement in bold…

Why would they recommend against additive for one diff and not the other when they both operate on the same principles?

So does additive do anything to address the uneven clutch wear? No, but it does make it easier for the clutches to glide on the friction plates, which will help reduce or eliminate chatter and prevent further wear.

The last thing I have to say is we work closely with a local drive train shop. The owner has been building and servicing driveshafts, differentials and complete axles for more than 40 years. That doesn’t make him the end-all authority when it comes to LSD’s, but any time we order a differential from him, whether it’s GM, Ford, Dodge, or other, he either includes an additive or tells us to make sure to put one in it. I tend to trust someone who has decades of experience - they’re not likely to stay in business that long if they weren’t good at what they do.

Again - this isn’t to say you HAVE to use additive - but despite GM’s warning against it, it’s highly unlikely to cause a loss of LSD functionality either.

mountainmanjoe

I don't abuse my axles, ie. I don't get water in them, or run them dry. I used my Astro extensively off-road, in the snow, sand, mud etc., and the LSD was ridden hard. I only ever put GL-5 in it. Never had chatter. The axle was working like new when the vehicle was totalled with 200k miles.
If the additive is purely to prevent nincompoops from complaining then they can keep it.


So, GM refuses to solve customer chatter problems, and would rather have a bunch of complaints about that, because the additive could cause a wreck?? C'mon. What kind of ****ty additive would that be. This is nonsense.

I'm reading that the GM fluid is pre-blended with FM, and that's why none needs to be added. I'm also reading that having too much FM is bad. It reduces friction to the point of making the clutches ineffective.

This information was ostensibly provided by an EATON engineer (the company who manufactures the gov-lock differential)
Source: https://www.dieselplace.com/threads/.../#post-5654969
I can neither confirm or deny this.


It is my understanding that unlike the G80 which is either engaged or disengaged (on/off), the G86 LSD is not governor actuated device, works on a different spring load principle, and the clutches are always engaged to some degree. So I would imagine the friction needs will be different too.

So in this situation, the G80 governor pawl is disengaged, no rotational force on the wave ramps, and no sideways clamping force on the clutches. In your manual transmission (dry) clutch analogy, it's a disengaged clutch.

Gumby22

Ok, here’s some clarifying statements. I often forget that light-hearted sarcasm isn’t always transferable via message board.

The causes I listed were based on what I’ve seen with customer vehicles - not a blanket statement for every LSD out there. If you don’t abuse them or allow contamination or low fluid levels, there’s no reason why you would’ve seen a failure unless it was caused by a problem you had no control over - a manufacturing defect, for example.

But not everyone is as adamant about vehicle care as you - some people just don’t know when there’s a problem until it’s too late. Axle lube tends to get thrown into the brake rotor hub which is also occupied by the parking brake shoes a d an area where dirt and dust collect. Unless the leak is bad enough to cause puddles, the leak isn’t even noticeable unless the rotor is removed because the dirt and dust inside the rotor hub soaks it up.

The whole wreck scenario was just a hypothetical situation. But if you think GM isn’t willing to ignore complaints then you’ve clearly never had to navigate a corporate phone system to reach customer service.

GM is a publicly owned company which means they are accountable to their shareholders - i.e. the bottom dollar - and customers are not their number one concern. If they were more concerned with customer care than stock price, problems related to cheaply manufactured parts that ultimately lead to recalls wouldn’t occur nearly as often.

Honestly, thank you for that link - I really didn’t know that GM fluid already has modifier in it. That obviously changes much of what I said in my previous post.

I really tried to find more info about GM fluid but my Google skills are awful and I wasn’t finding anything in details on websites that sell it.

I was posting on the ASSumption that GM fluid was just synthetic gear oil and there was nothing different about it other than it had a GM/AC Delco label on it.