Brown stain on inside of outer rear bearing

[RF_Burns]

I pulled the passenger side mid rear hub yesterday to install my Lenzi mid-rear disk brake system. Upon examining the bearings I noted a brown stain
on the inside of the outer bearing where it rests on the spindle. Its on about 1/4 of the inside circumference.

See photo here:
http://www.gmcmhphotos.com/photos/lenzi-mid-axle-disk-brake-upgrade/p67915-installing-dave-lenzi-mid-axle-disk-brake-upgrade.html

I don't see any scoring or evidence of heat. The rear bearings where replaced about 2 years ago with new Timken bearings, but with cancer and Covid
they have less than 3,000 miles on them.

The grease I used was a Valvoline product for wheel bearings with descriptions "Extreme pressure and temperature with moly and lithium for vehicles
with disk brakes" so I'm thinking it should be up for the job. The grease has not separated.

I have not yet cleaned out the entire bearing, but I cannot see any pitting etc.

Any opinions on this brown stain.
--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that

 

[Matt Colie]

Bruce,

Some years back, I lost a wheel (wheel, tire, brake drum and hub) in Arkansas. We searched, but never found the errant piece. There was evidence of
moisture - not much - on the spindle. Ever since, I have been very aware of moisture in the rear bearings and have often seen evidence but never seen
actual corrosion damage. What that stain may be is the result of a very small amount of moisture that either was left in during the prior assembly or
made its way in later. The amount of water that stain represents would have been less than a mm3 (cc/1000).

That brown is the color that is from Fe2O3, I am also seeing the black color of FeO2. FeO2 is the precursor of the brown rust color. The reason that
there is some black and some brown is that was all the water that was available. I will end my discussion of the corrosion of iron here because it
starts to get complex past here.

Matt
--
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit

 

[john r. lebetski]

I read that moly when exposed to high temps oxidizes and the oxidized byproducts do not have lubricating properties and in presence of moisture in air
promote corrosion of the rubbing surfaces. If you did not set up wheel bearing lash correctly (loosen to pin if needed after finger tightening, never
tighten) or overtemped the brakes this could happen.
--
John Lebetski
Woodstock, IL
77 Eleganza II