Sterling 10.5 eating on itself.

thatguy69

thatguy69

New member
Went to check the rear end in my fummins as I'm going over the truck for a upcomming trip, and find my magnet covered in metal material. So I pull that cover and the only thing I find is it looks like the steel plate from my limited slip is eating into the diff. Wondering what you guys think would cause this, along with am I able to run this thing for a bit longer? I checked it 5k miles ago and she was clean.
 

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Supposed to hit the road for a 12 hour trip next week fellas, could use some advice if anybodys got some.
 
Drain plug looks completely normal to me. I’d bet mine looks as bad or worse with only a few thousand miles on it.

I can’t speak on the carrier wear. Can’t tell from the pic myself.
 
thatguy69 said:
Thanks fellas, gonna dump some royal purple in it and send it.
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Don't waste your money on purple gold.


Likely, the "eating itself" you're seeing is the machine work when the housing is machined out to accept the LSD components. Manufactures leave those sharp/thin casting areas alone. Some areas show through more than others because the cast part is not perfect. The LSD in my 05 is that way from AAM.

I also just went down this road with my 05 after changing rear pinion seal but didn't post about it. The rear diff started making a weird growl sound when load was initially applied to the ring gear. Once ring gear had load, no growl. Pulled plug, it looked a little worse than yours. Dumbfounded at what the next step was, I pulled the carrier and pinion for inspection. Nothing wrong with bearings, races, or gears.

Went to a local guy who only works on manuals transmissions and axles. We talked through the scenarios, and it came down to fluid. I initially purchased 75W-90 SuperS synthetic gear oil because that’s what the service manual states to use, and that’s what the local parts store had. Local axle guy said never use synthetic gear oil, and only use the heaviest weight fluid you can find. So, I flattened out the crush sleeve some, set the pinion preload, set the gears back up, added 4 quarters of 85w-140 Castrol (non-synthetic) and drove it. Also changed front diff fluid to 85w-140 at the same time. Fluid was golden, but the housing and inside of diff cover had a brownish color film on them that wiped off easily.

The rear axle growling noise is now gone. I’ve pulled loaded trailers several hundred miles now without issues. I sent samples of the used and virgin 75w-90 fluid to be analyzed. The used fluid had a few more ppm of iron than the new fluid. But the new oil did have a low flashpoint, unlike the used oil. Apparently, a low flash point is not concerning, but notable. I won’t go into details about the gear oil lube discussion I had with the local axle guy. But his 40 years of knowledge opened my eyes to gear lube oils.

I've sense purchased two cases of 85w-140 walmart brand for the other trucks. Everything is going to have diffs serviced this month.

I was down to only my 91 12v for transportation. Motivation to fix the issue was great!
 
Red Sleeper said:
Don't waste your money on purple gold.


Likely, the "eating itself" you're seeing is the machine work when the housing is machined out to accept the LSD components. Manufactures leave those sharp/thin casting areas alone. Some areas show through more than others because the cast part is not perfect. The LSD in my 05 is that way from AAM.

I also just went down this road with my 05 after changing rear pinion seal but didn't post about it. The rear diff started making a weird growl sound when load was initially applied to the ring gear. Once ring gear had load, no growl. Pulled plug, it looked a little worse than yours. Dumbfounded at what the next step was, I pulled the carrier and pinion for inspection. Nothing wrong with bearings, races, or gears.

Went to a local guy who only works on manuals transmissions and axles. We talked through the scenarios, and it came down to fluid. I initially purchased 75W-90 SuperS synthetic gear oil because that’s what the service manual states to use, and that’s what the local parts store had. Local axle guy said never use synthetic gear oil, and only use the heaviest weight fluid you can find. So, I flattened out the crush sleeve some, set the pinion preload, set the gears back up, added 4 quarters of 85w-140 Castrol (non-synthetic) and drove it. Also changed front diff fluid to 85w-140 at the same time. Fluid was golden, but the housing and inside of diff cover had a brownish color film on them that wiped off easily.

The rear axle growling noise is now gone. I’ve pulled loaded trailers several hundred miles now without issues. I sent samples of the used and virgin 75w-90 fluid to be analyzed. The used fluid had a few more ppm of iron than the new fluid. But the new oil did have a low flashpoint, unlike the used oil. Apparently, a low flash point is not concerning, but notable. I won’t go into details about the gear oil lube discussion I had with the local axle guy. But his 40 years of knowledge opened my eyes to gear lube oils.

I've sense purchased two cases of 85w-140 walmart brand for the other trucks. Everything is going to have diffs serviced this month.

I was down to only my 91 12v for transportation. Motivation to fix the issue was great!
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Dam, thanks for the response. Wished I'd of known that on the gear lube but I guess I know what to use from here on out. Glad you got yours straightened out
 
I’ve used the cheapest shit on the shelf for almost two decades. Never had a problem related to fluid. I use what I make at work now just for the hell of it. Usually supertech.

You would be surprised at the fluid that goes into multiple brands of bottles and sells at a wide range of prices. Same shit they just charge more for the name on the bottle. Kind of like Nikes. No more quality than the china Velcro Walmart joints but 10 times the price haha
 
bateman said:
You would be surprised at the fluid that goes into multiple brands of bottles and sells at a wide range of prices. Same shit they just charge more for the name on the bottle. Kind of like Nikes. No more quality than the china Velcro Walmart joints but 10 times the price haha
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Years ago we sold two brands of engine oil. A cheap one and Rotella. Sales for the cheap brand where way lower because, according to the logic of most of our customers, the cheaper brand must be no good. We just keep Shell now.
 
Snedge said:
Years ago we sold two brands of engine oil. A cheap one and Rotella. Sales for the cheap brand where way lower because, according to the logic of most of our customers, the cheaper brand must be no good. We just keep Shell now.
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I’ve found that true in many scenarios, just not always.

I like the Rotella myself. Shame I have to buy it at Walmart for $13 a gallon instead of anywhere else for $22 a gallon. I enjoy supporting one of the last family owned auto stores in town, but I ain’t gonna spend double.
 
What did the axle mech have to say about the synthetic?

My rigs get water logged too often to run anything meant for longer intervals so I’ve never used it. Just curious.
 
Red Sleeper said:
What weight are you using?
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Calls for 75w 140 so that's what she got. The only reason I went royal purple was because it actually came out to be about the same price vs buying 3 quarts plus the friction mod additive. The royal purple supposedly already has the friction modifier in it, although it needs more as I can feel rear grabbing on tight low speed turns now.
 
bateman said:
I’ve found that true in many scenarios, just not always.

I like the Rotella myself. Shame I have to buy it at Walmart for $13 a gallon instead of anywhere else for $22 a gallon. I enjoy supporting one of the last family owned auto stores in town, but I ain’t gonna spend double.
Click to expand...
Same here. Local Napa is family owned and has a machine shop in back. I walk in and ask the owner for advice on stuff all the time and he has plenty of it to offer. I try to buy there all I can but sometimes you gotta draw the line.
 
bateman said:
What did the axle mech have to say about the synthetic?
Click to expand...

In summary he stated synthetic differential fluid is not suitable for a 3/4 ton full floating axle gear sets. It’s too thin.
Back in the 50's, 60's, 70's era, he stated the old STP differential fluid would leave a string of fluid from the housing to the drain pan when you removed the cover. Similar to molasses being poured from a bottle to your waffle. The side of the bottle is always sticky from that string that’s left hanging. Those old differentials were all clean, no real issues, and ran for decades on that oil. Once in a blue moon he will have a 60’s model vehicle in the shop for a differential service. He said once you pop the cover off, it’s obvious if the fluid has ever been changed. All usually very clean and shiny inside, a sign of original fluid.

Today’s differential fluid does not have that consistency. Only the friction modifier seems to have a similar consistence, which is basically whale oil. He uses an inexpensive 85w-140 from a 55gal drum in all differentials that he services. From sports cars to 5 ton trucks. Only real reason for a lighter gear oil is fuel economy. How do you improve fuel economy? Less drag/friction. The newer engines have tighter tolerances and can use a lighter weight oil that your typical 12v Cummins, which needs 15w-40. Think about your differential(s). Has anything really evolved in a ring and pinion application over the last 50 years? Have tolerances become tighter and backlash decreased with today’s ring and pinions? Not really. So why have oils become lighter? Fuel economy.

The only notable change I learned about in these AAM axles (Dodge & GM) is the two-cut or five-cut gears patterns. The five cut tooth is shorter at the toe and taller at the heel (OD & ID). Two-cut is the same height at the tow and heel of the gear. Backlash and bearings are all still similar, no change in tolerance to my knowledge.
 
Just got back from my trip, all went well. Plan on dropping the purple shit and having a look out of curiosity. Along with I wanna get the good stuff in there.
 
I wouldn't drain fresh 75w140, run it the cold months coming and swap it next spring. RP isn't worth the money, but It's probably good stuff.
 
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