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Discussion Starter · #1 ·
I've been Googling the heck out of this, and haven't found much in the way of reliable information. In fact, none.

I tried searching on here, too, but to no avail. So ...

A while back, while my engine was out for a rebuild, I put a Spartan locker in my AMC 20. I finally took it out for its first road use since the rebuild. Ran into a problem with the pax rear axle (too much end play), so I turned around and headed home. There was almost 3/16" end play (I found out it was due to a missing thrust block ... it was not mentioned in the locker instructions, and they said do NOT use thrust washers - so, it didn't go back in). The bearing didn't LOOK bad, but it didn't sound happy, and plenty of gear oil was contaminating the brakes with predictable results.

I noticed the gear oil (O'Reilly's 80W-90) leaking out of the tube was black. Not just dark, but black as coal. I found a couple of posts via Google saying it's no big whoop, run with it. Otherwise, I just find "shrugs" and a lot of guessing.

Does anyone know if this is the result of the locker install? Like stuff coming off the locker (kinda like mill scale?)? I have never in 40+ years of wrenching on vehicles encountered this situation. Nasty gear oil, yes, but usually resulting from water addition, rust, or a combination. I didn't pull the carrier, so lash is not an issue.

I'm going to end up changing the gear oil anyway, as I am going to one-piece axles (the engineer who thought the two-piece axles were a good idea needs to be flogged). I'm wondering, though, is the next batch of oil going to do the same thing? Should I be concerned, or just "roll with it"?
 

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I'm guessing the new oil washed some of the old cruddy oil off the tube walls and wound up coloring it.
 

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generally dark oil is a sign of over heated oil. You say the bearings seem unhappy. If the preload was to much pin or carrier that would cause over heating or gear mesh issue as well can heat things up fast. I aways monitor a new dif build with a IR gun. since a new dif needs break in and heat cycling.
 

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Discussion Starter · #5 ·
Thank you all for the input!

It's possible this is a combination of things. Dirty oil from the previous batch, locker "break-in" residue, and perhaps some heating up thanks to excessive end play.

So, more O'Reilly's 80W-90 it is.
 

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Sometimes if something is walking around enough to side load a seal it can rub some off into the oil and colour it. I've run into that a couple of times. Pretty rare though.
 

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Discussion Starter · #7 ·
Well, I popped the cover this afternoon, and what came out was pretty, light-honey colored oil. I'm guessing what was between the inner and outer seals on the pax side was just what was nasty. The driver's side was pretty clean, too, but there was only a tiny bit of end play there.

Now, just need new axles ...
 

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So factory 2 piece axles when you put the locker in? Thrust block does not equal thrust washers. Thrust block is in the center of the diff and the 2 piece axles butt up agains the block and then end play is set on one side. Thrust washer is between the spider/side gears the side of the carrier, some lunchbox lockers re-use them, some do not. if you are replacing axles, i would do with 1 piece. as for the black lube, it was washing out all of the crud and brake dust that had accumulated next to the wheel seal. Normal for the lube coming out the end of the axle tube to look extra nasty.
 

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Discussion Starter · #9 ·
So factory 2 piece axles when you put the locker in? Thrust block does not equal thrust washers. Thrust block is in the center of the diff and the 2 piece axles butt up agains the block and then end play is set on one side. Thrust washer is between the spider/side gears the side of the carrier, some lunchbox lockers re-use them, some do not. if you are replacing axles, i would do with 1 piece. as for the black lube, it was washing out all of the crud and brake dust that had accumulated next to the wheel seal. Normal for the lube coming out the end of the axle tube to look extra nasty.
I figured out what the deal was with the thrust block too late. As I said, I followed the instructions, and they mentioned NOTHING about the thrust block, so I omitted it when installing. I was not, at the time, overly familiar with the ins/outs of AMC 20s. I have learned much in the last week.

I have already ordered the one-piece axles; they should be here this week.

I tried to disassemble the two-piece axles. Not happening. Both pretty much laughed at my efforts with a 12 ton press. Fortunately, I had already dismantled the bearing cages and pulled the rollers out so I could retrieve the backing plates. I wanted those off the axles for two reasons: first, good used ones are hard to find and the new ones basically don't exist, and second, I didn't want to risk damaging them on the press.
 
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