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Did the gear lube wreck my differentials?

buickwagon

SM 2017
Full Member
Joined
Dec 5, 2017
Messages
131
Location
Muskoka, On
Last fall, I changed fluids in both diffs and the transfer case. Royal Purple 75w90 in the diffs, GM Autotrak II in the transfer case.

Near the end of winter, I started to notice a faint growl that I thought might be the first sign of a u-joint going. Crawled underneath in the snow, but couldn't locate a problem. A week or two later, 3 hours from home, there was a big "bang" as I accelerated onto the highway, followed by massive vibration. I coasted to the shoulder, reached underneath and found the rear of the driveshaft had a LOT of play. I assumed the u-joint had failed, but gear lube was pooling underneath the diff. 

Long story short: the rear diff input bearing grenaded. Chunks damaged gear teeth. $3000 to have the rear diff rebuilt by a drive-line shop. Talking to the mechanic, I noted that there was no sign of excessive wear just a few short months prior. He asked what weight fluid I used, and told me that in his experience this kind of damage can occur when 75w140 is used. Some people figure it must be better because it covers a wider range. Since I used 75W90, I really didn't think too much more about it and just chalked things up to bad luck and high mileage.

A few weeks ago, I started hearing an ominous growl from the front. Crawled underneath, u-joints were fine, play at the input bearing, oil fling line coming from the seal area. Oh oh. I pulled the fill plug and dipped my finger into some very shiny grey goo.

The local wreckers found me a low-mileage replacement in nice shape for a tenth of the price the rear rebuild cost, and I swapped it in (which was an adventure unto itself, but that's a different story...)

Last fall, there was a bit of fuzz stuck to the magnetic drain plug, but the fluid looked OK. So I'm left wondering what could have caused both differentials to fail at the same point in such a short span of time? And the only common factor I can think of is the gear lube.

Comments? Suggestions?
 
What AVY? 1500 or 2500?
What is mileage?
Were you using front end much? IE auto or 4wd?

What does manual say you should use? (My Memory is saying front and rear use different weight oil but that may be for 2002 only - I am getting old!)

Any offroading lately or agressive acceleration?

G80 rear or not?
 
My thoughts would be if you used the proper weight gear oil, regardless of brand or whether it was syn or not, if your gears were old then it was just their time.
 
ygmn said:
What AVY? 1500 or 2500?
1500

ygmn said:
What is mileage?
~350,000 kms (210,000mi)

ygmn said:
Were you using front end much? IE auto or 4wd?
I did use Auto a fair bit over the winter -- maybe 15-25% of the time. A lot of my driving is on ice- or snow-covered roads. Used 4wd high a few times getting up an icy driveway. Used 4wd low twice -- once just to try it, once to get unstuck. Not used at all since the snow melted.

ygmn said:
What does manual say you should use? (My Memory is saying front and rear use different weight oil but that may be for 2002 only - I am getting old!)
Front calls for 80W90, Rear calls for 75W90 synthetic. I used 75W90 in both.

ygmn said:
Any offroading lately or agressive acceleration?
No off-roading (not counting wet, muddy driveway in the spring). I'm pretty easy on the accelerator, use the whole ramp to get up to highway speed and keep close to the speed limit. I have hauled my compact tractor on it's trailer a few times -- about 3,400 lbs total.

ygmn said:
G80 rear or not?
G80 -- limited slip clutch pack + Eaton locker. (I was surprised to learn that both are in there. I was under the impression it was one or the other.) 
 
That is a lot of miles... and the rear end is a weak point in the drivetrain...
And things do not last forever...

Maybe weird timing.
 
buickwagon said:
1500
~350,000 kms (210,000mi)
I did use Auto a fair bit over the winter -- maybe 15-25% of the time. A lot of my driving is on ice- or snow-covered roads. Used 4wd high a few times getting up an icy driveway. Used 4wd low twice -- once just to try it, once to get unstuck. Not used at all since the snow melted.
Front calls for 80W90, Rear calls for 75W90 synthetic. I used 75W90 in both.
No off-roading (not counting wet, muddy driveway in the spring). I'm pretty easy on the accelerator, use the whole ramp to get up to highway speed and keep close to the speed limit. I have hauled my compact tractor on it's trailer a few times -- about 3,400 lbs total.
G80 -- limited slip clutch pack + Eaton locker. (I was surprised to learn that both are in there. I was under the impression it was one or the other.)
75W90 should have worked just fine in both ends.  Noisy front is typical with high miles.  Typically the seals start leaking and then they get run low on lube.  Had to replace my front with used one at 135,000.  Pinion bearing in rear sounds odd - no reason for that to go out the way it did (after 210,000 miles) unless rear was run low at some point for extended period.

A G80 is a gov-lock rear.  It does have one clutch pack in it, but it does not operate the way a clutch type Eaton posi does and it does not require the posi additive.  With the G80 the centrifugal weights apply the clutch pack all at once when one wheel starts to spin faster than the other (more than a certain amount required to throw the weights) - lockup is either on all the way or completely off.  Conversely, with an Eaton clutch type posi the two clutch packs always pre-loaded with a spring pack to provide a constant amount of lock-up between the rear wheels.  Traction overcomes this lockup during turns and this is why the real posi rears tend to chatter without the posi additive.  So the posi rear attempts to prevent the wheels from starting to turn at two different speeds, and the Gov-lock reacts to the wheels already turning at two different speeds by suddenly locking in the spinning wheel.  This is why they are lovingly known as Gov-bombs!  As you can imagine, this type of rear does not work well for racing!  But nothing you have done would explain the pinion bearing failure.

Have any of the Royal Purple left that could be tested?  ? or maybe retrieved from the old front diff?
 
2004Slickside said:
Pinion bearing in rear sounds odd - no reason for that to go out the way it did (after 210,000 miles) unless rear was run low at some point for extended period.
I found it hard to understand too. I'm pretty sure it was full -- no sign of leakage after I changed the lube a few months prior. Lots of lube dumped on the ground after it failed and took out the seal.

2004Slickside said:
A G80 is a gov-lock rear. 

The G80 RPO code seems highly dependent on model and/or year. For example, my Roadmaster Estate Wagon has RPO G80, but in that case it refers to limited slip, not locking.


2004Slickside said:
It does have one clutch pack in it, but it does not operate the way a clutch type Eaton posi does and it does not require the posi additive.  With the G80 the centrifugal weights apply the clutch pack all at once when one wheels starts to spin faster than the other
Ok, so the clutch pack is after the locking mechanism and only applies once the locker engages? That makes a certain amount of sense.

Interestingly, the drive-line shop did add the additive to the lube (or at least: to the bill  ???). I noticed that engagement is smoother since the rebuild, now I wonder if that is why?
 
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